Topic: Cell phone interference: how can I shield against it / what's wrong with my rig?

[whatboutbob]

Ok folks, this is going to be a bit of a novel, because there's a bit of detail to go into.

Short story is: I'm getting a lot of cell phone interference on about half of my recordings and I'd like to stop it, cos its ruining otherwise perfectly good recordings and driving me crazy.  Any help would be appreciated.

I've read all the threads on this subject on this board, and almost revived an old thread but decided to create this one because the old thread hasn't seen a post for 6 months.

I suspect this is more of an issue for me than most of you lot because most of the cell phones in Australia are on a GSM network...I believe that's not the case in the US (pls correct me if I'm wrong).

First point to make is that the interference is not caused by my phone, which is off at all times during recording.  The interference is from those lovely people around me.  I've tested at home and am picking up cell phone interference from up to 10 meters away (I haven't tested any further than that).

I've run hundreds of tests using the following equipment in different combinations:

Mics: at943 bodies with at853 caps (mini xlr ends)...I believe the cable is standard (it has 'audio technica' written on it), but they're only 4 feet long.
Power: homemade 3 wire battery box (as per Grame Cogger's schematics) and Church Audio 3 wire bb / preamp
ADC / pre: AD20
Recorder: iriver H120 * 3 (yeah, I've tested on all three of 'em)

The tests werent terribly scientific, but I tried to be as consistant as possible...I basically recorded silence with different combos, placed a phone nearby, made lots of calls, and noted the levels in Asobe Audition before and during the resultant interference.

I won't post all the data, unless someone wants it, but what I've found most enlightening from these results is that a particular mic into a particular channel sees more interference than when the mics are switched around.

So for example, with this config:

Mic 1 (R), Mic 2 (L) > Church audio bb/pre > H120 (with 20dB gain both channels): Base Levels: -57dB (L), -60dB (R).  Levels w/ interference: -36dB, -58dB

...whereas if I switch the mics around:

Mic 2 (R), Mic 1 (L): Base Levels: -58dB (L), -60dB (R). Levels w/ interference: -48dB, -40dB

The same bears out with all other combinations - ie if I apply the 20dB gain using the Church audio Pre, or replace the pre with my homemade bb, or add the AD20 after either of the bb's.

I can't figure out why this would be the case, so would appreciate any advice.

One other thing to throw into the mix, which i'm not sure is pertinent...one of the lead Rockbox developers (LinusN) has mentioned that some iriver units are not grounded correctly, though he was talking with regards to  tiking introduced to recording by plugging in the remote: "...the problem is that the analog and digital ground are connected on the ticking units...most likely a mistake, since there is still a resistance.".

If you've gotten this far, thanks for reading.

[rokpunk]

turn your phone off.

[it-goes-to-eleven]

I always get nervous when the person next to me starts taking pics with their phone or, worse, calls someone so they can hear the show.. So far I have not noticed anything that I would attribute to phones.  But interference from a phone 30 feet away.. Wow!

First question...  What gear are you using that is not shielded?  The plastic cases on battery boxes and small preamps may be an indication that their is no shielding. There might be a shield under the plastic but probably not.  You might try repeating your test while running the mics into a shielded device like a ua5, v3, whatever.

At this point I'd try and isolate it to your mics, your bbox, your cables, or the iriver. Maybe repeat the test with no mics and just the iriver+patch cord.

Have you verified that all of your cables have shields and that the shields are well grounded?

[guitard]

turn your phone off.

the interference is not caused by my phone, which is off at all times during recording.

[nic]

only thing I can think that will keep your gear interference free is to build something like a faraday cage and keep your gear in it during a show.

[whatboutbob]

Thanks for your advice thus far guys.  I just broke out a few other knick-nacks to test with.  Something I've just found that is particularly galling, is that my Giant Squid Audio Omni mics > matching battery box > iriver gets no interference. At first I thought it may be because the bb is in a metal box, so I tried leaving the top of it off, but still no interference.  Now, onto Freelunch's questions:

I always get nervous when the person next to me starts taking pics with their phone or, worse, calls someone so they can hear the show.. So far I have not noticed anything that I would attribute to phones.  But interference from a phone 30 feet away.. Wow!

First question...  What gear are you using that is not shielded?  The plastic cases on battery boxes and small preamps may be an indication that their is no shielding. There might be a shield under the plastic but probably not.  You might try repeating your test while running the mics into a shielded device like a ua5, v3, whatever.

At this point I'd try and isolate it to your mics, your bbox, your cables, or the iriver. Maybe repeat the test with no mics and just the iriver+patch cord.

Have you verified that all of your cables have shields and that the shields are well grounded?

The AT853 mic cables have shields. I did the soldering on the mini-xlr ends myself, and it looks ok...but...there's every chance I could've screwed something up.  In my favour though is that I've got another pair of older AT853's that I haven't taken a soldering iron anywhere near, and I still get interference running them > AT8505s > PS2 > AD20 (also w/o) > iriver.  The interference is definitely louder with the mics plugged in tho.

Homemade 3 wire bb: Definitely not shielded. I built it in a plastic box cos I couldn't find a metal box to fit it in.  Because of the interference I thought I had screwed up the grounding somehow and I don't know enough about this stuff to troubleshoot very well, so after ripping things to piece time and again I got the church audio bbox/pre.

Church Audio 9100 bb/pre: Again, plastic...I haven't opened it up but I doubt it is shielded.

PS2: The interference running everything through this isn't as bad, but it is still there.

Would love to run into a fully-shielded device, but damned if I know where I could get one.

So...where does that get me?  Because the GSA mics are clean, does that make it safe to rule out the iriver as the problem?  I also tested with a patch cable running out of the iriver...clean again.

If so, that leaves us with the mics and/or power.

I guess I could build a Y cable (or whatever its called) to run from my mic mini-xlrs to a 1/8 jack so that I could run them directly into my iriver to isolate them?  If that gets a clean bill of health then its definitely the power supplies...right?  Can y'all think of any other way of going at it?

I've got some copper shielding tape lying about. Could I potentially use that to shield the power supplies?  If so, how would I ground it?  If its not grounded it would act like an antenna, wouldn't it?

Thanks again.

[it-goes-to-eleven]

Cool - I think that mostly rules out the iriver for now.

At this point.. I'd try and put everything except the at853's in a big metal box that is gounded to a water pipe or electrical ground (careful).  Maybe an old tool box, or PC case. Maybe do it two ways - once with the electronics in the box and again with the mics and cables in the box.

There could still be something more funky going on with grounds in the cable, etc, but hopefully this will narrow it down further.  I suppose it is possible that the bbox/pre is sensitive and maybe the mic cables are carrying the signal into it.. If so, putting it into the box may not help.

[whatboutbob]

Ok, a cooking pot served the purpose.

Whole kit in the pot: no interference

Mics/cables out of the pot, iriver/church audio b/pre in: interference (though this *could* be attributed to an incomplete seal)

I suppose I should do it the other way around (mics in the pot) just to be sure. I'm off to bed though.  Just woke my gf by pottering around in the bathroom.  Does it say something about me that she walked into the bathroom @ 2am to see me putting my mics in a giant pot in the sink and she didn't say a word...just turned around and went back to bed...

[Brian Skalinder]

Just woke my gf by pottering around in the bathroom.  Does it say something about me that she walked into the bathroom @ 2am to see me putting my mics in a giant pot in the sink and she didn't say a word...just turned around and went back to bed...

   She's a keeper! 

[Humbug]

Brilliant, just briliiant +t for the girl

[whatboutbob]

Ah.. A cooking pot.  Of course!

That's good progress.  I think a reverse test would be the next step to make sure the seal wasn't to blame - mics in and boxes out.

Also, a test where the mics and bbox/p are in the pot but the mic cables are out and exposed might help. Another test would be poking just the mics out with the cables/bbox/pre in.  Might tell you whether it is the cables or the mics.

Just tried mics in, the rest out. Interference resulted.

Could I wrap stuff in aluminium foil for a better seal?

Will try again with the other tests tomorrow night...I think I'm pushing my luck with my better half. ;-)

Thanks again for all your help.

[SparkE!]

Your problem could be due to grounding of the shield to signal ground at both ends of the cable, thereby causing a ground loop.  You could try lifting the shield ground at the mic end of the cable.  If that's not possible, try lifting the shield from signal ground at the other end of the mic cable.  If that reduces the interference, then you know you've got a ground loop issue and we can continue troubleshooting from there.

[Digital Quality]

First thing I would try is taking mic cables completely out of the mix. Hook the mics directly into the pre and give it a shot.
Next put the cables back and hold the phone close to the mics or maybe borrow different mics from a friend.
Same thing for the pre.

Seems like you should be able to move your phone up and down the line while someone is ringing you and the interference will get stronger as you get closer to the leak.

[whatboutbob]

Your problem could be due to grounding of the shield to signal ground at both ends of the cable, thereby causing a ground loop.  You could try lifting the shield ground at the mic end of the cable.  If that's not possible, try lifting the shield from signal ground at the other end of the mic cable.  If that reduces the interference, then you know you've got a ground loop issue and we can continue troubleshooting from there.

I'd rather not do this at the mic end...I think I'd break something.

To 'lift the shield' at the mini-xlr end, do I just snip the shield in the mic cable at the mini-xlr and tape it up?

First thing I would try is taking mic cables completely out of the mix. Hook the mics directly into the pre and give it a shot.
Next put the cables back and hold the phone close to the mics or maybe borrow different mics from a friend.
Same thing for the pre.

The mics aren't detachable. They've got 4 ft of cable attached to 'em.  Don't know any other tapers in this country.

Seems like you should be able to move your phone up and down the line while someone is ringing you and the interference will get stronger as you get closer to the leak.

Moving the phone was my first thought...the problem is the interference isn't a consistant strength/length.  I can leave everything exactly as is, call 3 times, and get three different levels of intereference.  Maybe if the mic cables were longer than 4 ft...

[Digital Quality]

Can you feed it a line in (no mic or cable) whilst Sheila calls you? Turn it off and back on may be another good way to get a signal but I think incomming call would still be the best. The phone sends stronger signals depending on distance to the tower and other traffic.

I do know some aussie sim racers but no tapers.

It's most likely in the cable because it's also the biggest antenna.

[Church-Audio]

Hi I heard about your problems my preamp, it is shielded with copper foil around the whole circuit board. Even though we use a plastic case. I would suspect that it might be the length of cable is acting as some kind of antenna for the cell phone aprox 860 MHz to 1.5 GHz 4 feet sounds just about right. Lifting the ground will not help (it will kill the bias voltage to the mic thus no sound. When you use your simple battery box with the mics do you get interference? (Make sure you crank the gain up on your iriver to be at the same level as my preamp) If your still having problems Send the mics and preamp back to me, I will look at them free of charge and ship them back to you if there is a problem with our preamp we will replace it or fix it. As for your mics if there is a problem there we will fix it for free as well.

 How long is and what type of cable are you using from my preamp to the A/D converter?

Chris Church

Your problem could be due to grounding of the shield to signal ground at both ends of the cable, thereby causing a ground loop.  You could try lifting the shield ground at the mic end of the cable.  If that's not possible, try lifting the shield from signal ground at the other end of the mic cable.  If that reduces the interference, then you know you've got a ground loop issue and we can continue troubleshooting from there.

I'd rather not do this at the mic end...I think I'd break something.

To 'lift the shield' at the mini-xlr end, do I just snip the shield in the mic cable at the mini-xlr and tape it up?

First thing I would try is taking mic cables completely out of the mix. Hook the mics directly into the pre and give it a shot.
Next put the cables back and hold the phone close to the mics or maybe borrow different mics from a friend.
Same thing for the pre.

The mics aren't detachable. They've got 4 ft of cable attached to 'em.  Don't know any other tapers in this country.

Seems like you should be able to move your phone up and down the line while someone is ringing you and the interference will get stronger as you get closer to the leak.

Moving the phone was my first thought...the problem is the interference isn't a consistant strength/length.  I can leave everything exactly as is, call 3 times, and get three different levels of intereference.  Maybe if the mic cables were longer than 4 ft...

[whatboutbob]

Hi I heard about your problems my preamp, it is shielded with copper foil around the whole circuit board. Even though we use a plastic case. I would suspect that it might be the length of cable is acting as some kind of antenna for the cell phone aprox 860 MHz to 1.5 GHz 4 feet sounds just about right. Lifting the ground will not help (it will kill the bias voltage to the mic thus no sound. When you use your simple battery box with the mics do you get interference? (Make sure you crank the gain up on your iriver to be at the same level as my preamp) If your still having problems Send the mics and preamp back to me, I will look at them free of charge and ship them back to you if there is a problem with our preamp we will replace it or fix it. As for your mics if there is a problem there we will fix it for free as well.

 How long is and what type of cable are you using from my preamp to the A/D converter?

Chris Church

Thanks Chris.  That's an extremely generous offer.

To be honest though, I don't think its your preamp that's at fault, so I would hate for you to feel obliged to look at this.  I get interference with 2 different sets of mics, my homemade battery box and through the PS2, along with your pre.  On the other hand, if you're still happy to look at it, then I'm not going to say no, because its frustrating me and my technical know-how is somewhat lacking.  Come to think of it though, if the issue is specific to Australia's cell phones, would you even be able to replicate/source the issue?

The cable I'm using from the pre to the AD is the two foot cable you supplied (unexpectedly).  It plugs into the AD20's XLR's via a one foot 'Y' cable.  Keep in mind though that I also get the interference without the AD20...just going direct to the iriver.

I don't think your cable length theory is the problem either.  I was getting interference using my old at853's w/ the original length of cable (25 feet?).  Just today I hacked them down to 6 feet and changed them to the 3 wire config. I grounded one at the mini-xlr end (I'm kinda simple and got on a roll and forgot I wasn't going to ground it) and didn't ground the other one.  They both get interference.

It kills me that the GSA omnis/battery box are the gear I have that don't get interference.

[rokpunk]

This cell phone interference is common. It happens every time I put my cell phone on top of any of my mixing consoles. It also happens if I mic up someone with a wireless lav mic and they have a cell phone/blackberry in their pocket. It also happens with wired mics. It happens when standing next to my self powered Meyer rig....it happens using cheapo "PA on a stick" systems. The only cure is to turn off your (and other peoples) phones. Shure and Audio Technica both know about the problem (been reported by me, plus lots of others, from what they tell me), neither has a solution as of yet.

Sheilding your head by wrapping it in an aluminum foil beenie is the only solution. It also protects you from evil alien life forms.

[Church-Audio]

I have had this problem with two way radios! I had keyed in my two way radio beside a console it muted the sound system! Very strange, it seems it overloads or causes some kind of oscillation. I have never had a problem with my cell phone on a console before or even near mics maybe it is certain types of phones or transmitter types. I guess this is why when you’re in a hospital they tell you to turn it off. Strange


Chris Church

This cell phone interference is common. It happens every time I put my cell phone on top of any of my mixing consoles. It also happens if I mic up someone with a wireless lav mic and they have a cell phone/blackberry in their pocket. It also happens with wired mics. It happens when standing next to my self powered Meyer rig....it happens using cheapo "PA on a stick" systems. The only cure is to turn off your (and other peoples) phones. Shure and Audio Technica both know about the problem (been reported by me, plus lots of others, from what they tell me), neither has a solution as of yet.

Sheilding your head by wrapping it in an aluminum foil beenie is the only solution. It also protects you from evil alien life forms.

[Church-Audio]

So it's safe to say it’s not the mics or your preamp. Have you tried a different recorder? If not give that a shot try using the line input on your computer if you do not have another recorder.

Chris Church

Hi I heard about your problems my preamp, it is shielded with copper foil around the whole circuit board. Even though we use a plastic case. I would suspect that it might be the length of cable is acting as some kind of antenna for the cell phone aprox 860 MHz to 1.5 GHz 4 feet sounds just about right. Lifting the ground will not help (it will kill the bias voltage to the mic thus no sound. When you use your simple battery box with the mics do you get interference? (Make sure you crank the gain up on your iriver to be at the same level as my preamp) If your still having problems Send the mics and preamp back to me, I will look at them free of charge and ship them back to you if there is a problem with our preamp we will replace it or fix it. As for your mics if there is a problem there we will fix it for free as well.

 How long is and what type of cable are you using from my preamp to the A/D converter?

Chris Church

Thanks Chris.  That's an extremely generous offer.

To be honest though, I don't think its your preamp that's at fault, so I would hate for you to feel obliged to look at this.  I get interference with 2 different sets of mics, my homemade battery box and through the PS2, along with your pre.  On the other hand, if you're still happy to look at it, then I'm not going to say no, because its frustrating me and my technical know-how is somewhat lacking.  Come to think of it though, if the issue is specific to Australia's cell phones, would you even be able to replicate/source the issue?

The cable I'm using from the pre to the AD is the two foot cable you supplied (unexpectedly).  It plugs into the AD20's XLR's via a one foot 'Y' cable.  Keep in mind though that I also get the interference without the AD20...just going direct to the iriver.

I don't think your cable length theory is the problem either.  I was getting interference using my old at853's w/ the original length of cable (25 feet?).  Just today I hacked them down to 6 feet and changed them to the 3 wire config. I grounded one at the mini-xlr end (I'm kinda simple and got on a roll and forgot I wasn't going to ground it) and didn't ground the other one.  They both get interference.

It kills me that the GSA omnis/battery box are the gear I have that don't get interference.

[it-goes-to-eleven]

Come to think of it.. I used to have a stereo that would once in a great while blast some trucker's CB at extreme volume as he drove past.  I'm pretty sure it was an illegal high output CB..  The signal bypassed the volume control and would just BLAST even when nothing was playing or even when you were playing very low volume.. It would sure get your attention.  Now the interesting part.. It was a Creek integrated amp. Really great little amp BUT I now see the significance of the wood cover.


Did you ever test with the cables out of the pot but the mics and the bbox/pre/iriver in?

[SparkE!]

 I would suspect that it might be the length of cable is acting as some kind of antenna for the cell phone aprox 860 MHz to 1.5 GHz 4 feet sounds just about right.

Anything longer than about 1/4 wavelength can inadvertently become an effective antenna, so any cable longer than about 3 1/2" can be the problem.

 Lifting the ground will not help (it will kill the bias voltage to the mic thus no sound.)

So these are not shielded cables? I was suggesting to lift one end of the shield or the other, but if the only ground is power ground, then you obviously can't do that.

So it's safe to say it’s not the mics or your preamp.

I get interference with 2 different sets of mics, my homemade battery box and through the PS2, along with your pre.

The cable I'm using from the pre to the AD is the two foot cable you supplied (unexpectedly).  It plugs into the AD20's XLR's via a one foot 'Y' cable.  Keep in mind though that I also get the interference without the AD20...just going direct to the iriver.

I don't think your cable length theory is the problem either.  I was getting interference using my old at853's w/ the original length of cable (25 feet?).  Just today I hacked them down to 6 feet and changed them to the 3 wire config. I grounded one at the mini-xlr end (I'm kinda simple and got on a roll and forgot I wasn't going to ground it) and didn't ground the other one.  They both get interference.

It kills me that the GSA omnis/battery box are the gear I have that don't get interference.

So why do you think that it can't be the mics or the preamp?  Aren't they always in the circuit when there is a problem?

[Church-Audio]

I dont think its the preamp or the mics because he has tryed a different battery box and mics and still has the same problem.
I don't know if he has tryed just going direct in without the d/a converter or if he has tryed a different recording device. I would think that because the preamps and mics have been switched that the problem would be elsewhere. IMO.


Chris Church

 I would suspect that it might be the length of cable is acting as some kind of antenna for the cell phone aprox 860 MHz to 1.5 GHz 4 feet sounds just about right.

Anything longer than about 1/4 wavelength can inadvertently become an effective antenna, so any cable longer than about 3 1/2" can be the problem.

 Lifting the ground will not help (it will kill the bias voltage to the mic thus no sound.)

So these are not shielded cables? I was suggesting to lift one end of the shield or the other, but if the only ground is power ground, then you obviously can't do that.

So it's safe to say it’s not the mics or your preamp.

I get interference with 2 different sets of mics, my homemade battery box and through the PS2, along with your pre.

The cable I'm using from the pre to the AD is the two foot cable you supplied (unexpectedly).  It plugs into the AD20's XLR's via a one foot 'Y' cable.  Keep in mind though that I also get the interference without the AD20...just going direct to the iriver.

I don't think your cable length theory is the problem either.  I was getting interference using my old at853's w/ the original length of cable (25 feet?).  Just today I hacked them down to 6 feet and changed them to the 3 wire config. I grounded one at the mini-xlr end (I'm kinda simple and got on a roll and forgot I wasn't going to ground it) and didn't ground the other one.  They both get interference.

It kills me that the GSA omnis/battery box are the gear I have that don't get interference.

So why do you think that it can't be the mics or the preamp?  Aren't they always in the circuit when there is a problem?

[SparkE!]

I dont think its the preamp or the mics because he has tryed a different battery box and mics and still has the same problem.
I don't know if he has tryed just going direct in without the d/a converter or if he has tryed a different recording device. I would think that because the preamps and mics have been switched that the problem would be elsewhere. IMO.

The way I understand, the preamp is always in the circuit.  Is that not the case?

[Church-Audio]

He has removed my preamp from the chain and he still gets the interference.

I dont think its the preamp or the mics because he has tryed a different battery box and mics and still has the same problem.
I don't know if he has tryed just going direct in without the d/a converter or if he has tryed a different recording device. I would think that because the preamps and mics have been switched that the problem would be elsewhere. IMO.

The way I understand, the preamp is always in the circuit.  Is that not the case?

[whatboutbob]

The way I understand, the preamp is always in the circuit.  Is that not the case?

There's always something between the mics and the iriver...whether it be the preamp, my homemade bbox or the AT8505s/PS2. They all get interference.  The PS2 less than the other two.

Can the at853's in the 3-wire config be powered by the iriver plugin power?  If so, could someone please tell me how to wire a 1/8 plug to 2 mini-xlr(m).  That way I can test with just the mics and iriver.

Unfortunately I don't have a different recorder.  Oh, I suppose my partner's got an iriver H10 I could use.  Only records to mp3...but it may be better than nothing for testing purposes.

I thought it was safe to say that it wasn't the iriver because I don't get the interference from the GSA mics (w/ ~5 foot cables)?

So these are not shielded cables? I was suggesting to lift one end of the shield or the other, but if the only ground is power ground, then you obviously can't do that.

Sorry...I don't know (showing my ignorance here but i thought shield/ground were interchangeable)...there's two yellow wires, two red wires and the shield/ground 'thing' wrapped around 'em.

Did you ever test with the cables out of the pot but the mics and the bbox/pre/iriver in?

I did, but unfortunately the slightly open pot-lid makes these tests inconclusive.  I had interference with everything, apart from when the whole kit was in the pot (ie the only time the lid was fully closed).

Maybe I should just wear the pot to gigs? ;-)

[Microbe]

Hi,

If you've got a soundcard on your pc with line in you can always try that as a recording device.  If you've got the right software you can turn the gain up and test the mics and boxes.  I don't know how it would work out, but in theory you should be able to do it.

[SparkE!]

Can the at853's in the 3-wire config be powered by the iriver plugin power?  If so, could someone please tell me how to wire a 1/8 plug to 2 mini-xlr(m).  That way I can test with just the mics and iriver.

Ahhh, so you're talking about poorlyconditiond's style of battery box, like this?



When you said 3-wire, I thought you were talking about 3 wires per channel, balanced, like is used in XLR mic cables. So, you're running unshielded or perhaps your ground is your shield.

...there's two yellow wires, two red wires and the shield/ground 'thing' wrapped around 'em.

Now wait a minute.  I thought we were talking about 3 wires.  There are 5?  Do you have a schematic of how this stuff is connected?  Maybe you do have separate signal ground and shield paths.

[whatboutbob]

Hehe...sorry for the confusion.

The battery box I made is very similar to Richard's, but is actually from schematics drawn up by Graeme Cogger:
http://taperssection.com/index.php?topic=57512.0

The AT cables have two red wires, two yellow and the ground.  In the 3 wire config the red wires go to pin 3, yellow to pin 2, and the ground to pin1.

Does that clear anything up?

[SparkE!]

+T for notchin up the g33k factor with a chalkboard schematic!!
love it!

Well, poorlyconditioned deserves that +T because it was his drawing.  I think he said that it was the chalkboard in the physics(?) lab where he works.  Here's where he keeps all of the info:

http://www.cs.uwaterloo.ca/~mannr/AT853/

But hell yeah! I got a good chuckle out of the great mix of modern technology with erasable manual media.

[poorlyconditioned]

I don't have a whole lot of other ideas on this..  I'm wondering if any of the at853's can operate without gsm interference.  If not, then there's no point in more headbanging. You might drop Chris at Soundpros a note.  Those guys sell a ton of at853's and I'll bet they have some experience with this.

The new AT853 series (U853 I think they are called), supposedly reject RF noise.  So that is probably what they are talking about.

So, I think you're going to have to live with it.  Or maybe do some circuit wizardry on the mic body and/or cable.  I've always seen an inductor/capacitor pair (a filter) on the miniXLR sockets in AT8531 powering modules.  I think these are *trying* to remove RF, but might not be doing a great job of it.

  Richard

[SparkE!]

I don't have a whole lot of other ideas on this..  I'm wondering if any of the at853's can operate without gsm interference.  If not, then there's no point in more headbanging. You might drop Chris at Soundpros a note.  Those guys sell a ton of at853's and I'll bet they have some experience with this.

The new AT853 series (U853 I think they are called), supposedly reject RF noise.  So that is probably what they are talking about.

So, I think you're going to have to live with it.  Or maybe do some circuit wizardry on the mic body and/or cable.  I've always seen an inductor/capacitor pair (a filter) on the miniXLR sockets in AT8531 powering modules.  I think these are *trying* to remove RF, but might not be doing a great job of it.

  Richard

Yes, this is a good idea.  You'd use series inductors in the signal path and shunt caps to ground.  It works even better if you choose an inductor that is series resonant at the frequency of interest and caps that are also series resonant at that same frequency.  If your rf interference is broadband, then you just want to pick inductors and caps whose series resonant frequencies are above any frequency of interest.  (Above their series resonant frequency, inductors will appear capacitive and capacitors will appear inductive).

[Sparge Master]

I get interferance from my cell phone when doing transfers tascam tape deck > fire creatpor (mini-me) > cpu also with my tascam da20 > apogee2496. I usually throw my phone in the other room before i deal with shit

[Sparge Master]

This also happens in my truck. I dont need to be in a call or getting a text message phones no days send shit all the fucking time. I hate them and wish for the old days of land lines

[whatboutbob]

Yes, this is a good idea.  You'd use series inductors in the signal path and shunt caps to ground.  It works even better if you choose an inductor that is series resonant at the frequency of interest and caps that are also series resonant at that same frequency.  If your rf interference is broadband, then you just want to pick inductors and caps whose series resonant frequencies are above any frequency of interest.  (Above their series resonant frequency, inductors will appear capacitive and capacitors will appear inductive).

* whatboutbob breaks out the "smart to dumb" thesaurus.

[Church-Audio]

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Chris Church

Yes, this is a good idea.  You'd use series inductors in the signal path and shunt caps to ground.  It works even better if you choose an inductor that is series resonant at the frequency of interest and caps that are also series resonant at that same frequency.  If your rf interference is broadband, then you just want to pick inductors and caps whose series resonant frequencies are above any frequency of interest.  (Above their series resonant frequency, inductors will appear capacitive and capacitors will appear inductive).

* whatboutbob breaks out the "smart to dumb" thesaurus.

[whatboutbob]

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

...and what it lacks in subtlety, it more than makes up for in fashion sense!

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Thanks again Chris.  I'll keep you in mind as a last recourse.  I'm sure you've got more profitable ways to spend your time.

[Church-Audio]

It is not always about profit I sold you a preamp. I will take the time to take a look and see if I can help you. You helped me when you purchased it from me. End of story so like I said if you get stuck I will try and see what I can do maybe between Me Sparke! and poorly we can come up with a solution for your problem.

Chris Church

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

...and what it lacks in subtlety, it more than makes up for in fashion sense!

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Thanks again Chris.  I'll keep you in mind as a last recourse.  I'm sure you've got more profitable ways to spend your time.

[poorlyconditioned]

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

...and what it lacks in subtlety, it more than makes up for in fashion sense!

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Thanks again Chris.  I'll keep you in mind as a last recourse.  I'm sure you've got more profitable ways to spend your time.

+T for the avatar.  Put the mics *and* your head in the pot.  Helps prevent messages from aliens too...

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

The next step would be to put some small capacitors on the miniXLR connectors in the battery box.  The pins are: 1 (ground), 2 (audio), and 3 (battery).  Put a small cap between 1 and 3 and between 1 and 2.  The value should be something like 22pF.  That is a *really* small value, but even something bigger like 100pF (0.1nF) should work to test it out.  Try that and see if it fixes the problem.  I'm suggesting this because just about every regular XLR connector I see has caps from the two signal pins to ground.  Maybe it just stabilizes the phantom power, but it is still worth a try on the miniXLRs.

Let us know...

  Richard

[whatboutbob]

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

Will do.

The next step would be to put some small capacitors on the miniXLR connectors in the battery box.  The pins are: 1 (ground), 2 (audio), and 3 (battery).  Put a small cap between 1 and 3 and between 1 and 2.  The value should be something like 22pF.  That is a *really* small value, but even something bigger like 100pF (0.1nF) should work to test it out.  Try that and see if it fixes the problem.  I'm suggesting this because just about every regular XLR connector I see has caps from the two signal pins to ground.  Maybe it just stabilizes the phantom power, but it is still worth a try on the miniXLRs.

Ok...will do.  I've already glued up my bbox, so I'll have to make up another one to test.

The only caps I could find that small are ceramic.  Is that an issue?

[Church-Audio]

Ceramic are not the best for audio but for this test they will do.


Chris Church

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

Will do.

The next step would be to put some small capacitors on the miniXLR connectors in the battery box.  The pins are: 1 (ground), 2 (audio), and 3 (battery).  Put a small cap between 1 and 3 and between 1 and 2.  The value should be something like 22pF.  That is a *really* small value, but even something bigger like 100pF (0.1nF) should work to test it out.  Try that and see if it fixes the problem.  I'm suggesting this because just about every regular XLR connector I see has caps from the two signal pins to ground.  Maybe it just stabilizes the phantom power, but it is still worth a try on the miniXLRs.

Ok...will do.  I've already glued up my bbox, so I'll have to make up another one to test.

The only caps I could find that small are ceramic.  Is that an issue?

[Humbug]

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

Probably no help at all, but I have never experienced cell phone interference on my recordings; I turn my phone off when taping, even once when I forgot to turn it off and someone called me, there's nothing on the recording.

This is for running both rigs below, one of which is similar, though simpler (no-pre or external A>D) to the rig whatboutbob is running. 3-wire bb was built by Sanjay.

[whatboutbob]

Bah Humbug! (sorry...I've always wanted to type that)

Do you know if your phone is GSM?

I do get interference running a very similar setup: AT943s > 3wbb > iriver.

I built the Y cable tonight so I ran at853 > Y cable > iriver.  Interference resulted.

So while it could be the Y cable, it does seem to point to the mics or mic cables that are the problem, rather than the iriver (ruled out because there's no interference running the GSA's into it) or the pres(s)/bboxes.

Will try building the new bbox on the w/e as per Richard's directions.  I've sent off the email to SP.

[Oysterhead00]

I had a GSA phone through Cell One and got interference on ANY type of microphone or speaker.  On conference calls at work I'd get a high pitched "waaaaaa (pause) waaaaa (pause) waaaaaa".  I got it on one recording and if I put my phone on my night stand before going to bed, It would cause the noise to come through my alarm clock.  It doesn't happen all the time so I assume it's caused by some regular interval connection check or something.  I recently switched over to Verizon (not sure waht type of phone it is) and after 3 months have had zero interference.  The good news is it would always stop if I turned it off and if it was on my far shelf in my cubicle (4' from the phone) it wouldn't interfere.  So it seems to be a GSA thing and has a very small radius of effect.

[SparkE!]

Do you know if your phone is GSM?

He's in Europe, so it will be GSM.  GSM phones tend to cause more problems with audio circuits if the high impedance points in the circuits are not bypassed with small caps like poorlyconditioned was mentioning.  He's right that a small capacitor would probably be a good choice.  You'll want to use low loss chip capacitors whose series resonant frequency is above the cellular band. (NPO or COG dielectrics have low loss at cellular frequencies.)  A typical 15 pF COG chip cap would have a series resonant frequency of around 2 GHz, so that would cover the 1900 MHz cellular band where your GSM phone probably works.

Will try building the new bbox on the w/e as per Richard's directions.  I've sent off the email to SP.

Yeah, I'm suspecting the battery box at this point too.

[whatboutbob]

The good news is it would always stop if I turned it off and if it was on my far shelf in my cubicle (4' from the phone) it wouldn't interfere.  So it seems to be a GSA thing and has a very small radius of effect.

Hrmm...they must put the phones on 'roids down here (Australia) then. I stopped testing at ~30ft.  Admitedly the interference was faint at that stage, but still audible.

One thing I've been meaning to ask again, that I mentioned in my initial post...does anyone have any ideas why different mics in different channels would have different strengths of interference?  I'm really just making stuff up now, but the interference couldn't somehow be leaking from the ground on one mic to the audio on the other...and its stronger in one combination because the mic 'a' ground pin is closer to the mic 'b' audio pin than the mic 'b' ground pin is to the mic 'a' audio'.  Bah, I'm prolly confusing you all and I guess it doesn't really matter.

He's in Europe, so it will be GSM.  GSM phones tend to cause more problems with audio circuits if the high impedance points in the circuits are not bypassed with small caps like poorlyconditioned was mentioning.  He's right that a small capacitor would probably be a good choice.  You'll want to use low loss chip capacitors whose series resonant frequency is above the cellular band. (NPO or COG dielectrics have low loss at cellular frequencies.)  A typical 15 pF COG chip cap would have a series resonant frequency of around 2 GHz, so that would cover the 1900 MHz cellular band where your GSM phone probably works.

I'm pretty sure Australia uses dual-band GSM: 900 and 1800MHz...I think it jumps between the two in high traffic areas.  Would that change the caps required?

edit: Looks ilke it: http://www.accesscomms.com.au/mobnet.htm

Now I've just gotta go google 'NPO or COG dielectric capacitors' cos i've never heard of 'em and don't think the local Ratshack equivalent has 'em...unless I'm going nuts...

Yeah, I'm suspecting the battery box at this point too.

I thought the bbox and Church Audio bbox/pre could be ruled out cos I still get interference without them in the mix (AT853s > Y cable > iriver)?

[SparkE!]

Yeah, I'm suspecting the battery box at this point too.

I thought the bbox and Church Audio bbox/pre could be ruled out cos I still get interference without them in the mix (AT853s > Y cable > iriver)?

OK, I missed that.  I'm having a hard time keeping up with the signal paths you've tried.

If you are still getting the interference when just using the plug-in power of the iRiver, then it almost has to be the mics themselves.  With that in mind, I'd recommend getting some bypass caps and simply install them between tip and ground and between ring and ground on your mic connector (which I assume is a 1/8" stereo plug?).

You're probably not going to find the caps you need at the local Radio Shack.  NPO and COG refer to temperature characteristics of ceramic dielectric material, but your reason for wanting those dielectrics is not for the low temperature variation of dielectric constant.  Instead, it's because those materials tend to have low losses at rf frequencies, so the caps are still good caps at those frequencies.  They also can be made to have fairly high self-resonant frequencies.  Plastic film caps may be what you want to use for coupling caps at audio frequencies, but they aren't of much use at rf frequencies because their self-resonant frequencies are usually too low for their impedance to remain capacitive at rf frequencies.  At rf frequencies, most plastic film caps would appear to be inductive.

I don't know who to suggest for a source of caps in Australia, but I'd be looking for either Panasonic or MuRata caps in a 0402 package size and a COG or NPO dielectric and maybe 15 pF of capacitance.  That would work for shunting either 800 MHz GSM or 1800 MHz GSM signals.

[whatboutbob]

Chris from SP was good enough to reply:
=================================================================
> I hope you don't mind me asking this random question, but I was wondering if you guys have had any reports of problems with RF interference with the AT943/AT853 mics?

Not yet...

>Me rambling about the problem...

If you run the mics balanced as you are with the Denecke, you have very little chance of interference.

If you run the 853's balanced with true phantom adapters, etc or with this box:
 
http://www.soundprofessionals.com/cgi-bin/gold/item/AT8532
 
you will be balanced and should not have this problem. I think the 3 wire mod you have still runs the mic unbalanced (but I am not 100% sure of this).
 
Also, AT is aware of this issue in some extreme cases, even with balanced cable, and has a new version of the 853 available. It's more expensive and the benefits are only apparent if you run balanced with their power supply.

===========================================================

My battery box should be (assuming I haven't screwed anything up) and the Church Audio pre is balanced...right?  That's the whole point of the 3wbb, isn't it?

[Church-Audio]

I think the solution Chris mentioned would be very expensive, you would need two converters $300 + a new preamp $$$$ I would try the caps first. If that does not work send back the preamp and your battery box and I will mod them so this does not happen again. I have sold 100's of preamps to the UK never had a problem, but I can see you are so I want to help get that stupid metal pot off your head

All mini three wire mic inputs are unbalanced. they have three conductors they are GROUND-SIGNAL-BIAS ( BIAS JUST A FANCEY WORD FOR POWER) what Chris at SP is talking about is a balanced converter that is three pin to XLR I do not personally think it will do anything more then a few well placed bypass caps. As a matter of fact balanced is + signal - and ground. The advantage is less chance of inducted interference for long cable runs. (Not an issue here) and more common mode rejection (a different issue here) but Like I said before I think this problem can be fixed with a simple mod (have you tried a different recorder?)

if you still have problems send me your battery box and my preamp and I will fix the problem for FREE with out spending $300 on converters there are tons of guys on here that run unbalanced inputs and never have a problem I think there has to be a simple solution that will not cost an arm and a leg.


Chris Church

Chris from SP was good enough to reply:
=================================================================
> I hope you don't mind me asking this random question, but I was wondering if you guys have had any reports of problems with RF interference with the AT943/AT853 mics?

Not yet...

>Me rambling about the problem...

If you run the mics balanced as you are with the Denecke, you have very little chance of interference.

If you run the 853's balanced with true phantom adapters, etc or with this box:
 
http://www.soundprofessionals.com/cgi-bin/gold/item/AT8532
 
you will be balanced and should not have this problem. I think the 3 wire mod you have still runs the mic unbalanced (but I am not 100% sure of this).
 
Also, AT is aware of this issue in some extreme cases, even with balanced cable, and has a new version of the 853 available. It's more expensive and the benefits are only apparent if you run balanced with their power supply.

===========================================================

My battery box should be (assuming I haven't screwed anything up) and the Church Audio pre is balanced...right?  That's the whole point of the 3wbb, isn't it?

[poorlyconditioned]

Chris from SP was good enough to reply:
=================================================================
> I hope you don't mind me asking this random question, but I was wondering if you guys have had any reports of problems with RF interference with the AT943/AT853 mics?

Not yet...

>Me rambling about the problem...

If you run the mics balanced as you are with the Denecke, you have very little chance of interference.

If you run the 853's balanced with true phantom adapters, etc or with this box:
 
http://www.soundprofessionals.com/cgi-bin/gold/item/AT8532
 
you will be balanced and should not have this problem. I think the 3 wire mod you have still runs the mic unbalanced (but I am not 100% sure of this).
 
Also, AT is aware of this issue in some extreme cases, even with balanced cable, and has a new version of the 853 available. It's more expensive and the benefits are only apparent if you run balanced with their power supply.

===========================================================

My battery box should be (assuming I haven't screwed anything up) and the Church Audio pre is balanced...right?  That's the whole point of the 3wbb, isn't it?

No battery boxes are balanced!

Balanced is what regular XLR cables are.

  Richard

[whatboutbob]

Right...my bad then. Clearly I have no idea what I'm on about.

Picked up some 15pF NPO dielectric caps today...will see if they make any difference tonight.

[Church-Audio]

Its that dam pot its not making you think straight

Chris Church

Right...my bad then. Clearly I have no idea what I'm on about.

Picked up some 15pF NPO dielectric caps today...will see if they make any difference tonight.

[whatboutbob]

Either that or aliens have fought through my shield...

[SparkE!]

Right...my bad then. Clearly I have no idea what I'm on about.

Picked up some 15pF NPO dielectric caps today...will see if they make any difference tonight.

What case style is used for the caps?  Are they leaded or are they chip caps?  If they are leaded, then you'll probably need a large electrical value, more like 22 pF or 27 pF in order to overcome the inductance of the leads.  Nonetheless, the 15 pF caps will still probably help if the rf interference is related to the mic cables.

On the other hand, if the interference is unchanged, then you're probably looking at needing to bypass the mic element itself.  There are back electret mic elements that come with 10 pF or 15 pF bypass capacitors installed inside the capsule specifically to avoid the problem of cellphone or radio interference.  One of the most common uses for these bypassed electret elements is the mic in cellphones, but I also remember a few years back that there was something in the news about hearing aids that were being driven crazy by cellphones.  There were lots of recalls on hearing aids when GSM was being deployed in Europe.  Apparently the cellphone interference would be played loudly into the ears of the person wearing the hearing aid.  Yikes!

[whatboutbob]

What case style is used for the caps?  Are they leaded or are they chip caps?

Errrrrrr....they look like clay....?

Ok...just got done testing with the 15pF caps across pins 1&2 and 1&3.  There's still a lot of interference, however it seems to be marginally lower than w/o the caps, though it is difficult to measure precisely due to the varying strength of the interference at any one time.

Should I try a different capacitance (sp?) cap?

[SparkE!]

What case style is used for the caps?  Are they leaded or are they chip caps?

Errrrrrr....they look like clay....?

Ok...just got done testing with the 15pF caps across pins 1&2 and 1&3.  There's still a lot of interference, however it seems to be marginally lower than w/o the caps, though it is difficult to measure precisely due to the varying strength of the interference at any one time.

Should I try a different capacitance (sp?) cap?

By case style, I meant do they have leads or are they chip caps with metalization for connection directly to the body of the caps?  If you are connecting by wire leads, then the ideal capacitance will be slightly more in order to overcome the lead inductance.

Regardless, if there was only a small difference, then you probably will not be able to make much difference by putting caps between the signal lines and ground, even with larger caps.  In that case the problem has almost got to be with the mic elements themselves.  You'd have to place the caps inside the mic elements in order to fix the problem.  It sounds like that's what AT is planning to do with their new design, so cellphone interference may just be a given with your current mic elements, which would be a bummer for you.  I'm pretty much out of ideas here unless you can talk AT into trading your old mics for the new ones.

[Church-Audio]

or send them to me

What case style is used for the caps?  Are they leaded or are they chip caps?

Errrrrrr....they look like clay....?

Ok...just got done testing with the 15pF caps across pins 1&2 and 1&3.  There's still a lot of interference, however it seems to be marginally lower than w/o the caps, though it is difficult to measure precisely due to the varying strength of the interference at any one time.

Should I try a different capacitance (sp?) cap?

By case style, I meant do they have leads or are they chip caps with metalization for connection directly to the body of the caps?  If you are connecting by wire leads, then the ideal capacitance will be slightly more in order to overcome the lead inductance.

Regardless, if there was only a small difference, then you probably will not be able to make much difference by putting caps between the signal lines and ground, even with larger caps.  In that case the problem has almost got to be with the mic elements themselves.  You'd have to place the caps inside the mic elements in order to fix the problem.  It sounds like that's what AT is planning to do with their new design, so cellphone interference may just be a given with your current mic elements, which would be a bummer for you.  I'm pretty much out of ideas here unless you can talk AT into trading your old mics for the new ones.

[whatboutbob]

Right, I've found my partner's phone emits more regular interference.  So using that I've run it up and down the length of the rig, and can confirm, that the problem is definitely the mic caps.

Thanks very much to all who have contributed.  I give up.  Chris, I'm going to take you up on your generous offer.  Wil email you shortly.

[Church-Audio]

Hey I just thought of another solution that "MIGHT" work create what is called a faraday shield by going to a hobby store and pickup some fine brass screen and make little mic pockets surround the mics in this fine brass screen I bet that will solve the problem.


If you don't want to try that it’s cool, but I think it might work. You can sew the screen togeather or use solder at the edges create a windscreen out of the stuff it should work, the problem is the front of the capsule is letting the inducted signal in. With the fine brass screen it will allow the sound to come in with out any effect, but will or may block the bad cell phone stuff from hapnin. Also it will allow you to take the pot off your head another added bonus!

Right, I've found my partner's phone emits more regular interference.  So using that I've run it up and down the length of the rig, and can confirm, that the problem is definitely the mic caps.

Thanks very much to all who have contributed.  I give up.  Chris, I'm going to take you up on your generous offer.  Wil email you shortly.

[whatboutbob]

Hey I just thought of another solution that "MIGHT" work create what is called a faraday shield by going to a hobby store and pickup some fine brass screen and make little mic pockets surround the mics in this fine brass screen I bet that will solve the problem.

I was initially looking at faraday cages when I thought the problem was with the iriver.  Didn't think about using it on the mics. I wonder if I can do this without screwing the sound?

Would I need to ground the cage somehow?  Otherwise wouldn't it act like an antenna?

Edit: hrmm...I wonder where I can source the mesh.  The local hobby shops don't seem to have it.

I may need to order from these guys: https://www.twpinc.com/twp/jsp/product.jsp?type=11# (some interesting info about RFI there too).

edit2: gah...just noticed the fine print...minimum order is $75. :-/

[Church-Audio]

This is where I get my mesh screen from http://www.ksmetals.com/Craft/Tooling_Foil_&_Mesh.asp

The screen does not need to be earthed if it is 100% around the mic it will still act as a shield. And it will not change the sound of your mics I use the same screen on my mic capsules to sheild them for this very reason Another trick of the trade.

Hey I just thought of another solution that "MIGHT" work create what is called a faraday shield by going to a hobby store and pickup some fine brass screen and make little mic pockets surround the mics in this fine brass screen I bet that will solve the problem.

I was initially looking at faraday cages when I thought the problem was with the iriver.  Didn't think about using it on the mics. I wonder if I can do this without screwing the sound?

Would I need to ground the cage somehow?  Otherwise wouldn't it act like an antenna?

Edit: hrmm...I wonder where I can source the mesh.  The local hobby shops don't seem to have it.

I may need to order from these guys: https://www.twpinc.com/twp/jsp/product.jsp?type=11# (some interesting info about RFI there too).

edit2: gah...just noticed the fine print...minimum order is $75. :-/

[it-goes-to-eleven]

GOOD hardware stores will sell 'hardware cloth' of various mesh sizes.  I'd suggest sandwiching the shield in shrink wrap. That may also allow you to avoid soldering or sewing the seam, etc. Any contact with the mesh with fingers/etc could cause handling noise by changing the inductance and capacitance of the ground plane. So having it covered isn't such a bad idea. I'd think you'd want to ground it but I'm not sure if you'd need to for these frequencies.

[Church-Audio]

Good ideas doe’s hardware cloth come in a very fine mesh? I have never seen it I would like to check it out if you know where I can get some. I think if the shield can be 100% or almost 100% now that I think of it it’s not a bad idea to attach it to ground somehow. I would try it with or without and see what happens. How would you heat shrink it with out interfering with the mics performance? Hey maybe it’s not a bad idea to use a windscreen under the brass screen or hardware cloth? I know lots of companies use this brass screen like Neumann and AT to name a few. It does work hardware cloth would be good too I think if you can find a very fine mesh the stuff I am talking about is finer then the permanent mesh coffee filters. Its looks like silk the holes can not really even be seen with the naked eye.

Chris Church

GOOD hardware stores will sell 'hardware cloth' of various mesh sizes.  I'd suggest sandwiching the shield in shrink wrap. That may also allow you to avoid soldering or sewing the seam, etc. Any contact with the mesh with fingers/etc could cause handling noise by changing the inductance and capacitance of the ground plane. So having it covered isn't such a bad idea. I'd think you'd want to ground it but I'm not sure if you'd need to for these frequencies.

[whatboutbob]

Its looks like silk the holes can not really even be seen with the naked eye.

Hrmm...by the photo that's what the stuff in the link I posted above looks like.  I'm having a hard time finding anything suitable.  By the looks of it there's nothing called 'hardware cloth' down here.

Does the mesh have to be brass or copper?  Could it be another metal?

If I can find something I was thinking I'd put a layer of it over a very thin pair of windscreens I've got.

[Church-Audio]

As long as the metal in question is a conductor, it should be fine. I would make sure you get the finest mesh you can find. Go to a cooking store and see if they have any strainers that are fine mesh they should. Buy one and cut out the mesh.

Its looks like silk the holes can not really even be seen with the naked eye.

Hrmm...by the photo that's what the stuff in the link I posted above looks like.  I'm having a hard time finding anything suitable.  By the looks of it there's nothing called 'hardware cloth' down here.

Does the mesh have to be brass or copper?  Could it be another metal?

If I can find something I was thinking I'd put a layer of it over a very thin pair of windscreens I've got.

[whatboutbob]

I would make sure you get the finest mesh you can find. Go to a cooking store and see if they have any strainers that are fine mesh they should. Buy one and cut out the mesh.

Mwaha...I'll leave that as a last resort.

edit: ok...so I got impatient and was getting bored with the enthralling England v Paraguay match, so my kitchen is now minus one strainer but my mics have two fabulous-looking RFI shields.

...but do they work, you ask?

Initial tests show a small decrease in interference while using the rf-doms (tm).

It gives me some hope if I can just find some finer mesh.

[whatboutbob]

grrr...ok...i found some finer mesh (2 x $1 tea strainers later).

I'm sad to report that the rfi is still there...marginally lessened...but still there.

I've had enough.  I'm looking at new mics (audix m1290c's seem to fit the bill).

I just have to cross my fingers that I don't get the same problems. 

Thanks again to those who've chipped in their advice on this thread.

[Digital Quality]

New mics are always a good idea anyway

I had another thought whilst driving to Wakarusa. I'm not sure if it's GSM but there used to be a protocol where the tower would commuinicate with the phone even when it was switched "off". The power only put it in a sleepy state and turned off the screen and such. The phone still woke up every now and then to check in with the tower. The only way to get it turned off completely was to take out the battery. Maybe just another thing to try at the next show.

Good luck with the new mics!!

[whatboutbob]

New mics are always a good idea anyway

Hehe...yeah...there is a small chance that all of this is actually an elaborate plot to psychologically justify that I must have new mics. To quote a fine 'made in australia' film..."there is no spoon"... 

I'm not sure if it's GSM but there used to be a protocol where the tower would commuinicate with the phone even when it was switched "off".

Thanks for the thought...I've read the same thing somewhere, but I'm 99% sure that's not the case with the aussie phone network and is not the source of at least the rfi i get on my recordins.  My reasoning:

a) I've never had speakers suffer from rfi while our phones are off (while its a fairly common occurence when phones are on)
b) usually when my recordings have rfi i hear it over my monitors and can place it to some wook within a few meters of me clicking ''send' to make a call or send a txt msg

[whatboutbob]

>Thank you for your inquiry and sorry to take so long getting back to you. Your message was routed to me while I was out of the office.   The GSM >interference issue has been a huge problem for the audio industry.  We addressed (and resolved) this in our revamp of the UniPoint line with the >UniGuard technology.  You may need to upgrade to the new UniPoint line to resolve your issues.
>Please let me know if you need additional information.
 
>Rick Jxxxxx
>Manager, Audio Solutions
 
>Audio-Technica U.S., Inc.

[whatboutbob]

Alas, but upon receipt of my new (to me) audix m1290 mics today I confirmed that cell phone interference is not an issue just with audio technica mics.

I think I'll just live with it until it kills an otherwise awesome recording again and then snap and buy some u853's or other supposedly rfi-protected mics.

Man this is frustrating (/expensive).

edit: fat fingers

[rokpunk]

Buy some Neumanns and see if that fixes the problem. It won't help with the cell phone interference, but at least you'll have some good mics.

[Church-Audio]

Send your stuff to me I am try and see if I can fix the problem.

 My offer still stands

Chris Church

Alas, but upon receipt of my new (to me) audix m1290 mics today I confirmed that cell phone interference is not an issue just with audio technica mics.

I think I'll just live with it until it kills an otherwise awesome gig again and then snap and buy some u853's or other supposedly rfi-protected mics.

Man this is frustrating (/expensive).

[jeromejello]

Alas, but upon receipt of my new (to me) audix m1290 mics today I confirmed that cell phone interference is not an issue just with audio technica mics.

I think I'll just live with it until it kills an otherwise awesome gig again and then snap and buy some u853's or other supposedly rfi-protected mics.

Man this is frustrating (/expensive).

that sure does suck... have you thought about using those rf shields that clip on to cables (i really dont know what i am talking about)
the ua-5 i have came with a plastic shield that clicks over a headphone cord when plugged into the unit.  

let it be known that:
a) i am not sure if this for the same thing
b) if it would have any other adverse effects on the mics
c) where to get them

+t for your crappy cellphones in oz

[whatboutbob]

that sure does suck... have you thought about using those rf shields that clip on to cables (i really dont know what i am talking about)
the ua-5 i have came with a plastic shield that clicks over a headphone cord when plugged into the unit. 

Funny you should mention that.  I got a ua-5 in the mail today too...saw the doohickey and thought I'd give it a shot on the mic cables.  It made no impact.

Send your stuff to me I am try and see if I can fix the problem.

My offer still stands

Chris: Thanks once again.  I didn't want to put you out, but it seems I've exhausted all other avenues apart from buying mics that I'll have to sell a body-part to fund, so I think I'll take you up on that very generous offer now.  Could you pls pm me your mailing address?

Right...I'm off to watch (on tv) Australia play in the second round of the world cup (who woulda thunk it?!).

[whatboutbob]

What a nightmare..  It would be good to learn which other mics/rigs are prone to this type of interference.. I'm wondering about 406x, etc...  I am guessing that SD mics with grounded metal bodies and balanced signals will do better (though the SP-C4 mics are not balanced).

Before you get too worried, just keep in mind that this seems to be fairly region-specific...or at least network-type specific (GSM) which seems like its not prevalent in the US.

[whatboutbob]

Ahh...didn't realise that.

[SparkE!]

Before you get too worried, just keep in mind that this seems to be fairly region-specific...or at least network-type specific (GSM) which seems like its not prevalent in the US.

There are definitely GSM cellphones in the US.  Many Blackberry devices are GSM as well as CDMA. Don't get too comfortable...

Ahh...didn't realise that.

Yes, but most of ours in the US are in the 1900 MHz band.  I think that Australia's GSM phones are mostly in the 800 MHz band, aren't they?  They use the same channel access protocols, but they are just in different parts of the rf spectrum.

[whatboutbob]

Yes, but most of ours in the US are in the 1900 MHz band.  I think that Australia's GSM phones are mostly in the 800 MHz band, aren't they?  They use the same channel access protocols, but they are just in different parts of the rf spectrum.

I'm not sure which band they're mostly in, but the network is dual band: 900 and 1800MHz

[SparkE!]

I'm not sure which band they're mostly in, but the network is dual band: 900 and 1800MHz

Oops, yes that's right.  I was thinking 900 and typed 800, but I didn't realize that GSM had gone dual band there.  I guess that makes sense with the use of smaller phones.  Europe is also 900/1800.

[willndmb]

i got cell phone probs for the 1st time at a show a week or so ago, the guy next to me was letting his friend listen in
not sure what picked up the signal
393 > UA-5 > JB3
i never had a prob in the past with people around using their phone, hope i don't again
lucky it wasn't to bad and only for a few seconds

[Unitmonster]

I never once had a problem with my UA-5>JB3 setup, including 2 recent radiohead shows that were cell-phone central.

[hyperplane]

I know I'm chiming in late and all. But for whatever this is worth (or not), here goes...

Recently while browsing around for some cables and such, to make some custom items, I saw some "RF protected" cables listed. Is it possible to simply re-wire the Audio Technica mics you have? (Or see if Chris Church can, or would be willing to, do this for you) ?

I know it's probably a dumb idea, and I don't know if this would even be a potential solution, but a few feet of cable isn't *that* expensive (surely cheaper than buying new mics) so I thought I'd throw the idea out there.

[whatboutbob]

thanks for piping in.

i'm pretty sure its the mic caps that are the problem tho (going by the jump in volume of the interference according to the proximity of the phone to the caps), so while RF-protected cables may help, but it won't eliminate the issue.

I haven't managed to get to the post office during the day yet, but will do so soon cos i'm keen to see if Chris can work some magic.

[jbraveman]

My DPA 4022 caps have the same problem in combination with nextel/blackberry service.

http://taperssection.com/index.php?topic=67991.0

[kuuan]

after reading through this thread I became curious if the Sound Professionals would use the new AT's UniGuard technology for their CMC mic line:
My questions may betray a beginner, but nevertheless, here what I had asked to the SP technical assisteance and the answers ( inbold ) I just received:

Hi, good morning,
 
there have been numerous reports of interference to recordings due to GSM cell phones.
 
In a statement of an official of Audio Technic I ran across it says:
'The GSM interference issue has been a huge problem for the audio industry.  We addressed (and resolved) this in our revamp of the UniPoint line with the UniGuard technology. You may need to upgrade to the new UniPoint line to resolve your issues.'
( of interference )
 
If I am not mistaken there is e.g. a new replacement of the AT853 which is called U853 incorporating the UniGuard technology.
I am very much interested in yout SP-CMC4 mics ( I prefer the small miniplug to the heavy XLR )
 
My question therefore is:
Will SP integrate the UniGuard technology in the SP-CMC line, resp. will there be a SP-CMC4 incorporating the UniGuard technology?
 
Yes, once they are available. AT has not yet made the new version available to the OEM market (us).

Or would that not make sense since the CMCs use unbalanced lines?
 
Unknown.....but my guess is that there would be little benefit since they are usually wired unbalanced. Of course, we do offer options to keep them balanced as well.
As for reports of interference, there are well over 1000 sets of these in the field.....I have personally heard of 2 occurrences of interference so far. ....mainly because the cable length on these is only 4 feet and the cable length on the regular model which is used for hanging over choirs is 25 feet or longer.
 
thank you for your attention,
 
If you have any additional questions, please let me know.
Best Regards,
.....

[jibooer]

just to put my .02 in, I would like to address the fact that some people are getting ticking on their CF card recordings from bleeding during the transfer of data during the recording...it is very similar to the sounds made by RF intereference. This problem has been brought to the attention of D.Oade in regards to some of the earlier models of the PMD-6**...

[kuba]

I can't get any cell interference no matter how hard I try.

AT831 (Audio-Technica 6 feet cables) > DIY battery box (two wire, 9V, plastic box, no shielding at all) > 1 foot cable (taken from Sony earbuds) > H120

Sorry if I'm too late or if it doesn't help anything, I didn't read all 7 pages of this thread.

[beathydrolysis]

I can't get any cell interference no matter how hard I try.

AT831 (Audio-Technica 6 feet cables) > DIY battery box (two wire, 9V, plastic box, no shielding at all) > 1 foot cable (taken from Sony earbuds) > H120

Sorry if I'm too late or if it doesn't help anything, I didn't read all 7 pages of this thread.

Are you using a GSM phone?  I think the intereference problem has been targeted to GSM phones specifically.  Unless you or someone you know has T-Mobile, you probably are not using a GSM phone and thus are extremely unlikely to generate the interference.  Most of the world is on GSM but in the states almost no one is GSM.  It's too bad GSM causes the interference cuz all around its a better type of network than CDMA and the other garbage we use in the US.

[kuba]

Are you using a GSM phone?  I think the intereference problem has been targeted to GSM phones specifically.  Unless you or someone you know has T-Mobile, you probably are not using a GSM phone and thus are extremely unlikely to generate the interference.  Most of the world is on GSM but in the states almost no one is GSM.  It's too bad GSM causes the interference cuz all around its a better type of network than CDMA and the other garbage we use in the US.

Yep, Vodafone GSM, 900/1800 MHz. I didn't do any sophisticated testing, I was just curious whether to switch of my phone during recording to avoid those awful sounds. I turned on my rig, dial my phone number on another phone and simply moved my phone around the hardware.

[SparkE!]

Are you using a GSM phone?  I think the intereference problem has been targeted to GSM phones specifically.  Unless you or someone you know has T-Mobile, you probably are not using a GSM phone and thus are extremely unlikely to generate the interference.  Most of the world is on GSM but in the states almost no one is GSM.  It's too bad GSM causes the interference cuz all around its a better type of network than CDMA and the other garbage we use in the US.

Yep, Vodafone GSM, 900/1800 MHz. I didn't do any sophisticated testing, I was just curious whether to switch of my phone during recording to avoid those awful sounds. I turned on my rig, dial my phone number on another phone and simply moved my phone around the hardware.

Try sending email or SMS.  That's what most people are complaining about.

Simply dialing another number does not cause you to get a GSM channel.  That doesn't happen until you establish the call or a data session.  With a live call, you also have to produce noise on your end of the call because GSM will not use the channel to transmit audio that is essentially silence.

[kuba]

Try sending email or SMS.  That's what most people are complaining about.

Simply dialing another number does not cause you to get a GSM channel.  That doesn't happen until you establish the call or a data session.  With a live call, you also have to produce noise on your end of the call because GSM will not use the channel to transmit audio that is essentially silence.

Ah, I see, that's pretty obvious, I'm a dumbass    Still, I've never caught an interference on my recordings.

[SparkE!]

thanks for piping in.

i'm pretty sure its the mic caps that are the problem tho (going by the jump in volume of the interference according to the proximity of the phone to the caps), so while RF-protected cables may help, but it won't eliminate the issue.

I haven't managed to get to the post office during the day yet, but will do so soon cos i'm keen to see if Chris can work some magic.

What's the status of this issue?  Did the magic work?  Are you interference-free now?

[it-goes-to-eleven]

Been wondering.. Anyone done any interference testing with the r09?

[SparkE!]

thanks for piping in.

i'm pretty sure its the mic caps that are the problem tho (going by the jump in volume of the interference according to the proximity of the phone to the caps), so while RF-protected cables may help, but it won't eliminate the issue.

I haven't managed to get to the post office during the day yet, but will do so soon cos i'm keen to see if Chris can work some magic.

What's the status of this issue?  Did the magic work?  Are you interference-free now?

Status guys? Did the mods work?  If so, what did you do?

[whatboutbob]

thanks for piping in.

i'm pretty sure its the mic caps that are the problem tho (going by the jump in volume of the interference according to the proximity of the phone to the caps), so while RF-protected cables may help, but it won't eliminate the issue.

I haven't managed to get to the post office during the day yet, but will do so soon cos i'm keen to see if Chris can work some magic.

What's the status of this issue?  Did the magic work?  Are you interference-free now?

Status guys? Did the mods work?  If so, what did you do?

Nope. No luck. Not sure what Chris tried though.  Seemed inappropriate to ask.

Am shopping around for better shielded mics now. 'tis difficult cos I don't know exactly what's poorly shielded about my current mics.  The only mics I can find that actively advertise being shielded are the new AT's.

[whatboutbob]

Try sending email or SMS.  That's what most people are complaining about.

Simply dialing another number does not cause you to get a GSM channel.  That doesn't happen until you establish the call or a data session.  With a live call, you also have to produce noise on your end of the call because GSM will not use the channel to transmit audio that is essentially silence.

I'm guessing Australia's network works differently because I get interference simply by dialling/receiving.

[SparkE!]

Try sending email or SMS.  That's what most people are complaining about.

Simply dialing another number does not cause you to get a GSM channel.  That doesn't happen until you establish the call or a data session.  With a live call, you also have to produce noise on your end of the call because GSM will not use the channel to transmit audio that is essentially silence.

I'm guessing Australia's network works differently because I get interference simply by dialling/receiving.

Dialing a number will not create interference until it is transmitted.  On most phones, that should not happen until you hit the "Send" button.  Receiving text can cause interference too because your phone has to acknowledge the receipt of each packet in the message.  Sending text should cause more interference than receiving text.  Whatever the case, the channel access protocols are the same in Australia as anywhere else that uses GSM.

Sorry to hear that the fix did not work.  I think Chris probably put capacitors on the output of the mic amps, right where the output is attached to your mic cable.  That's a good place to start, but a better place to put the caps is probably on the input to the mic amp.  The problem with that is that it can affect your mic's sensitivity and may also affect the frequency response.  It depends on the topology of that amp.  Also, care should be taken to minimize the inductance of the ground path back to signal ground of the amp.  Feedthroughs on the board can represent 2 to 4 nH of inductance and a typical trace will have perhaps 1 nH per mm of length.  It depends on the thickness of the trace.  The smaller the trace, the higher the inductance.  Anyway, the parasitic inductance of the board traces can affect the effective impedance of the capacitors and move their self-resonant frequency to a lower frequency.  The caps were chosen so that they would have series resonance in the center of the GSM band, creating a virtual short to ground at that frequency.

Whatever you get for mics, good performance around GSM phones will rely on not only good shielding, but good rf bypassing around the active elements in the mic amp and good rf separation between shield ground and signal ground.

I don't know about how your mic cables are set up, but I'm assuming that they have a pair of signal wire (+ and -), a signal ground and a shield ground.  If so, it's common practice to isolate shield ground from signal ground at one end of the cable or the other.  If it's hum you're fighting, then you usually separate them at the mic end of the cable.  If it's rf you're fighting, then it's common to separate them at the far end (not the mic end) of the cable.  You might look into whether you can disconnect the shield from signal ground at one end of the cable or the other.

If on your cables, signal ground = shield ground, then maybe you can replace the cables and get better results, leaving shield ground separated from signal ground at the destination end of the cable.

Regardless, sorry to hear that the mods didn't work.  I was hoping for good results with a simple fix.

[whatboutbob]

Simply dialing another number does not cause you to get a GSM channel.  That doesn't happen until you establish the call or a data session.  With a live call, you also have to produce noise on your end of the call because GSM will not use the channel to transmit audio that is essentially silence.

Dialing a number will not create interference until it is transmitted.  On most phones, that should not happen until you hit the "Send" button.  Receiving text can cause interference too because your phone has to acknowledge the receipt of each packet in the message.  Sending text should cause more interference than receiving text.  Whatever the case, the channel access protocols are the same in Australia as anywhere else that uses GSM.

Ah...ok...I think we've got definitions of 'dialling'.  The 'dialling' I was likely incorrectly referring to is after I or the other person click 'send'.  So we are in agreement.  Having said that, I've also noted and been able to replicate (though not with my phone so it may be another network type) interference when no active transmissions have been going on - ie the incoming/outgoing texts/calls.  I think the phones are 'touching base' in an attempt to get a signal...why I've got no idea.

Sorry to hear that the fix did not work.  I think Chris probably put capacitors on the output of the mic amps, right where the output is attached to your mic cable.  That's a good place to start, but a better place to put the caps is probably on the input to the mic amp.  The problem with that is that it can affect your mic's sensitivity and may also affect the frequency response.  It depends on the topology of that amp.  Also, care should be taken to minimize the inductance of the ground path back to signal ground of the amp.  Feedthroughs on the board can represent 2 to 4 nH of inductance and a typical trace will have perhaps 1 nH per mm of length.  It depends on the thickness of the trace.  The smaller the trace, the higher the inductance.  Anyway, the parasitic inductance of the board traces can affect the effective impedance of the capacitors and move their self-resonant frequency to a lower frequency.  The caps were chosen so that they would have series resonance in the center of the GSM band, creating a virtual short to ground at that frequency.

Whoosh...I'm afraid most of that all went sailing over my head. I'll try to translate it some time soon when its not 2am.  Before sending the mics off to Chris, as per advice in this thread i I did try placing various caps across various pins with little success.

Whatever you get for mics, good performance around GSM phones will rely on not only good shielding, but good rf bypassing around the active elements in the mic amp and good rf separation between shield ground and signal ground.

I don't know about how your mic cables are set up, but I'm assuming that they have a pair of signal wire (+ and -), a signal ground and a shield ground.  If so, it's common practice to isolate shield ground from signal ground at one end of the cable or the other.  If it's hum you're fighting, then you usually separate them at the mic end of the cable.  If it's rf you're fighting, then it's common to separate them at the far end (not the mic end) of the cable.  You might look into whether you can disconnect the shield from signal ground at one end of the cable or the other.

If on your cables, signal ground = shield ground, then maybe you can replace the cables and get better results, leaving shield ground separated from signal ground at the destination end of the cable.

Regardless, sorry to hear that the mods didn't work.  I was hoping for good results with a simple fix.

To be honest, I'm not sure how my audix cables are setup (am yet to hack into 'em)...but they are the 'standard' cable that ships with the mics.  I do know my AT853s are in the '3 wire' config because I hacked them myself after being frustrated by brickwalling (blindly following instructions kindly laid out by Richard I believe).  What '3 wire' means has all been explained to me patiently in the past...but right now I can't recall what that means for ground.  I do know one of the first things I tried after getting sh!tty with the interference was to 'lift the ground' after doing some digging around ancient threads on here. Not even sure if I did it right tho.  I think I just disconnected the 'ground' from the pin at the amp-end.  This resulted in a hum and did nothing to improve the interefence (I think it actually got worse).  Argh...anyways...I'm off to bed.

Once again...apologies for my noobness and thank you very much for taking your time to talk me through these issues.