Topic: Cellphone noises? What causes this?

[colargol]

Hi!

I taped a show today, and for the first time in years I got those cellphone noises on my recording. Is it because:

• I forgot to put my phone in flight mode? (I normally always do)
• it was the first time I recorded bringing my new iphone 6?

Or is it one of the elements in the equipment I used:

• Schoeps MK41s
• Nbob actives
• Naiant Tinybox
• Minijack to minijack from Darktrain
• M10

Any input appreciated...

-colargol

[colargol]

When you have unbalanced connections near cellphones, I would worry about interference.

Thanks Jon.
So basically, with this setup, I just have to be careful about having a cellphone nearby? It is related to the distance from the cellphone, right? Because today the cellphone was about 6-8 inches away from recorder/preamp, which is where it normally is, but in flight mode...
-c

[ScoobieKW]

When you have unbalanced connections near cellphones, I would worry about interference.

GSM cell signals in particular are problematic. In the US that's AT&T and T-Mobile.

Airplane mode is best solution, but to mitigate Jon's advice is accurate.
The weak link in your setup is the unbalanced connection from Tinybox to the M10. This is the cable that should be short and coiled.

[ScoobieKW]

Airplane mode is best solution, but to mitigate Jon's advice is accurate.
The weak link in your setup is the unbalanced connection from Tinybox to the M10. This is the cable that should be short and coiled.

The Nbox cables are also unbalanced.

Good to know. I ran into this a while back. A friend who uses AT&T was leaving her purse near my rig. Took a bit for me to convince her that she should move it.

[Marshall7]

I know this is close to heresy...but you could just leave the damn phone at home!

[yates7592]

Switch the f***er off.

[colargol]

I know this is close to heresy...but you could just leave the damn phone at home!

It is pretty close to heresy, yes... I need the phone for lots of stuff these days. Where I live most (relatively young) people buy their bus/subway tickets on the phone, and my wife would probably not like it if I left her and the kids with no option to be contacted. Anyway, I can switch it off, or put it in flight mode, so that I can take photos, but the difficult part is to convince everyone around me to turn it off ;-)

Like I said, I have not had any trouble with this the past few years, using flight mode on my own phone. I guess people around me are too far away to create any interference in the recording.

[colargol]

Inverse square law--every doubling in distance from the source of interference drops the signal 6dB.  Your phone was six inches away; other peoples' phone are probably six feet.  That means their signal is 20dB lower than yours at your recorder.

Thanks, that explains why the interference was so loud on my recording yesterday - the phone was very close, and the music was not amplified, so I had the tinybox on "high", which I almost never do... This is nice to know.

[Scooter123]

I think the culprit is unbalanced connections and the SD Card.  Eliminate either, and the problem is solved.  I've sat next to a Taper with a Tascam DR-2D who suffered from immense static interference while my rig, a Sony M-10 was immune.  The Sony records to internal memory, not an SD Card

I wonder if the new UHS-II SD cards, with a really fast write speed would eliminate write bursts and static. 

[Marshall7]

The Sony records to internal memory, not an SD Card

It can...but not everyone runs in like that.

[blg]

fwiw, I run exactly the same rig as the OP (except my mini to mini is from Jon and it locks on the Tinybox side) and have done well over 100 shows with my iPhone in my left pocket (on) and my M10 recording to the SD card in my right pocket.  Up to this point, I have never had cell phone interference.  I have verizon if that makes a difference. 

[Jamos]

fwiw, I run exactly the same rig as the OP (except my mini to mini is from Jon and it locks on the Tinybox side) and have done well over 100 shows with my iPhone in my left pocket (on) and my M10 recording to the SD card in my right pocket.  Up to this point, I have never had cell phone interference.  I have verizon if that makes a difference.

Verizon uses CDMA technology, which does not exhibit itself in the same "interference" sounds that GSM signals do.  (i.e. if you have Verizon you shouldn't even worry about it)
In my experience, even moving the phone a few inches away from the cable will stop the interference from happening.  Having your phone in your left pocket and your recorder/cables in your right pocket (using your body as an RF blocker), you will likely never get the interference.

Still, always throw the phone on airplane mode when recording (esp. if you are at a show)...watch the show not the device!

[yates7592]

You also have to worry about the guy stood next to you, the serial texter or facebook addict.

[Karl]

I'm on Verizon and do have issues with noise. Airplane mode is the answer.

[kleiner Rainer]

I think the culprit is unbalanced connections and the SD Card.  Eliminate either, and the problem is solved.  I've sat next to a Taper with a Tascam DR-2D who suffered from immense static interference while my rig, a Sony M-10 was immune.  The Sony records to internal memory, not an SD Card

I wonder if the new UHS-II SD cards, with a really fast write speed would eliminate write bursts and static.

SD cards are no more sensitive to RF fields than built-in memory. Both use the same form of serial interface (in fact, you can read and write SD cards with the SPI interface built into many contemporary microcontrollers). Most card sockets are shielded, BTW. A designer would have to be very incompetent to make an SD card interface RF sensitive - in fact it would not pass CE RF immunity regulations!

I do EMC tests regularly, and in my experience the main problem in this case is a weak shield of the unsymmetrical wiring. Some time ago when recording under a railway catenary of 15000V AC I had hum problems. I found out that the shield of the mic cable was not good enough. After replacing it with a better cable the problem was solved. Tip: measure the shield resistance from end to end with a good ohmmeter. I found that the ubiquitious ready made stereo cables from far east had a rather high shield resistance. Copper is expensive. Going to a show to record it too. So I built my own interconnects with high quality materials.

BTW I operate a portable transceiver for ham radio (4 times the RF power of a mobile phone) with a plug-in micro SD card to store audio and GPS tracks - and that card is built right into a transmitter! Never had a problem.

Greetings,

Rainer

[rjp]

Also, regarding GSM carriers (mostly AT&T and T-Mobile in the US), the old 2G phones and networks are the worst for interference, with its characteristic "buzz-buzz-buzz! buzz-buzz-buzz! BzzzzzZZZZZZZZZZZZZZZ!" raising a racket. The 3G (UMTS) and 4G (LTE) phones are nowhere near as bad, but you still don't want RF sources right up close to your recording rig.

[DSatz]

Resistance to interference is "all relative." Even the best fully professional equipment can never, on its own, be absolutely, 100% resistant to all interference. People need to realize that it's just asking too much of the equipment.

In general, the setups that are safest from interference are those that are balanced from end to end. All other things being equal, balance is more important (effective) than shielding. But balanced setups can have "pin 1" problems, depending on the design of the equipment you're using (which is why Neutrik "EMC" series XLR connectors were invented and should be used much more widely in my opinion). And ultimately, even balanced setups with no pin 1 problem can still suffer from interference if the source is strong enough and nasty enough in terms of its spectrum and spikiness.

With an unbalanced setup you are just a sitting duck, and the only defense you have is your hope that no offending signal sources will come within range.

The distance formula (inverse square law), cited above, sets the stage. But the mechanism of interference is that the RF signals are rectified (detected) across some junction in the circuit and then amplified--and detection is a threshold phenomenon in terms of voltage. Given any particular source of interference and any point in a circuit where it might be detected, if you're beyond the corresponding threshold distance, you're basically safe as long as the signal stays the same. But if the interference source gets nastier and/or moves closer to the point of detection, the resulting interference will increase disproportionately as the threshold voltage is crossed.

So you really do have to keep cell phones and other mobile electronic devices away from the equipment and the cables--all the more so when unbalanced equipment is being used. Shielding is nice, but niceness doesn't help much against a signal that's basically like a rapidly spinning Ninja blade being thrown at it.

--best regards

P.S.: I don't see how the storage medium (SD card, etc.) could be an issue, since by the time any writing occurs there, the signals have already been digitized. Even if the interference were somehow strong enough to disrupt the data writing process, the result wouldn't be an analog of the detected interfering signal.

[John Willett]

(which is why Neutrik "EMC" series XLR connectors were invented and should be used much more widely in my opinion)

Agreed - which is why every new XLR cable I have is now terminated with Neutrik EMC XLRs.

I started moving over to these as soon as they came out - there s too much RF floating about nowadays and people at concerts Tweeting and updating Facebook - it's a nightmare.

[DigiGal]

I still endorse using Neutriks EMC series connectors with low capacitance double shielded starquad mic cables as a defense for this.  Cell phones are everywhere these days and good luck trying to get everyone around you to turn off their GSM phones for a performance.  High quality input transformers are also recommended, especially if you ever use long cable runs.  It is much better to prevent interference than to try and remove it once it has been recorded. 

http://www.neutrik.com/en/xlr/xlr-cable-connectors/emc-series/