Topic: What is causing my 'digi-noise' throught this recording?

[Neilyboy]

First off grab this quick sample from here:

http://neilyboy.mtco.com/doug/diginoise.mp3

I am using a set of Panasonic WM-61A caps that I performed the 'linkwitz' mod (reversing the polarity, to get less distortion with higher spl) > home made battery box > home-made ipod line-in connector hack (http://www.sparkfun.com/commerce/product_info.php?products_id=704) > ipod nano (rockboxed). Keep in mind im I just going for 'cheap' and 'tiny'.

My main goal (after I figure out if this diginoise can be corrected) is to rig up some 61a caps in a hat to a female 1/8" mini-plug which can all be worn without discomfort or looking to obvious. So I am then able to run a M/M 1/8" cable from the plug to a battery box in a pocket then out to the recorder. I do not want to get into the 'why'. Yes this would produce nothing worth sharing but its honestly just for 'giggles' although I am impressed with just how well the cheap little 61a's perform. Ok onto the recording and question itself.

This recording was done only as a test to see just how 'stealth' I could be on a sub $100 budget. This recording was doomed from the beginning as I was only asked to go to the show about 2 hours before it started and I lived an hour away. Then when we arrived all the seats were filled except the two seats stage left and below the speakers in the room. So this recording was done at butt-level as it was rigged up in a hat that I sat on the seat next to me. This had no chance at getting a decent pull but I wanted to try it out to see how it would work. See picture here to see my position in the room.

I was basically behind and to the right of the stage in the back corner of the room.


The reason I am posting this here is to find out just what is producing this 'diginoise' which is very annoying throught the recording. Do not mind the 'white noise' which is heard throught the entire recording (this was caused by me having to run the recorder at +25 gain as the venue was not what I expected it to be). It was a very 'comfy' venue which seated only about 40-60 people. The music was very quiet and hard for the caps to pickup.

The noise I am asking about starts around the 0:33 - 1:11 mark of this sample. It comes and goes throught the entire recording. I am just wondering if it was caused by something not being shielded properly or what. I am going to run some more tests on it at home tonight to see if running different mics / power supplies to the ipod produce the same noise and then go from there (as it may be an issue with the home-made, line-in dock connector). I was just curious to see if anyone has had similar experiences and heard something similar?

I figure I can narrow it down by eliminating things from the mic's to the bb to the connector but thought I would throw this out there to see if someone would know just what I should be looking at first.

Thanks for the read and if I need to provide any other info just ask.
Neil

[db]

sounds more like rf interference than diginoise.

[Neilyboy]

if that is the case could this be 'helped' by using some better 'shielded' cable while rigging up the mic's? I have a roll of belden mic cable (a little thicker than I was wanting to use) but if it fixes this issue then I would find a way to make it work. I am still going to run some tests at home to see if it is present in a different environment. I have about 10 caps left and some spare time this weekend so I may try throwing together some other rigs to see what happens. I am doing this mainly because I get a kick out of recording, as well as see quite a few live local shows and would love to have something that I could casually wear on me and record with at the same time.

thanks for your input.

neil

[db]

set up your rig to record and have your cell ring near it and see what gets captured.
better shielding helps but it ain't magic if the interference is strong enough. you may just have a bad wire/connection though.

[Neilyboy]

thanks for the thoughts db. I did have my cellphone in my left pocket which was about 2' from the recording gear at all times this evening! I will deff have to look into this further! thanks again.

Neil

[Neilyboy]

The PA sounded fairly clean. The strange thing was I was almost directly below the speaker with the mics pointing out toward the room (probably picking up a lot of Doug's monitor's as well). I wish I was home now or had brought the rig here to work with me to tinker with it. I will have to play around a bit tonight. As for the cellphone it was just on in my pocket. I had no data come or go during the entire show unless the phone goes out and hits a tower for time and date info or something like that every now and then there would have been no tx/rx data from my phone.

on a side note. what would be the best way to 'amplify' the signal before inputting it to the ipod? Is there a preamp I could build for a few bucks that would help with the gain issues I was having so I would not have to boost the gain up so I on the recorder that I get a consistent white noise throughout the entire recording??

neil

[Church-Audio]

if that is the case could this be 'helped' by using some better 'shielded' cable while rigging up the mic's? I have a roll of belden mic cable (a little thicker than I was wanting to use) but if it fixes this issue then I would find a way to make it work. I am still going to run some tests at home to see if it is present in a different environment. I have about 10 caps left and some spare time this weekend so I may try throwing together some other rigs to see what happens. I am doing this mainly because I get a kick out of recording, as well as see quite a few live local shows and would love to have something that I could casually wear on me and record with at the same time.

thanks for your input.

neil

One of the tricks I use on the back of a capsule is Copper foil tape... I make a little cup out of it then place the whole thing in a brass tube then epoxy it all together makes for a very effective shield. You can solder one end of the foil cup with your shield wire. The other end of the cup sticks to the sides of the capsule.

Chris

[Neilyboy]

what type of epoxy do you suggest Chris. I purchased some stuff that was supposed to be flexible as well but the junk never set for me it just stayed like a liquid snot. It was just a one part epoxy nothing special (supposedly just a squirt and let dry product) (i would have to dig up the tube if i still have it, i may have thrown the stuff out by now, but want to say it was made by GE).

I think i picture in my head what you mean by using come copper foil. Would i slit a whole in it for the cable to go through then wrap it around the sides of the capsule?

Take care and thank you so much for your help as I do appreciate it!

Neil

[sunjan]

what would be the best way to 'amplify' the signal before inputting it to the ipod? Is there a preamp I could build for a few bucks that would help with the gain issues I was having so I would not have to boost the gain up so I on the recorder that I get a consistent white noise throughout the entire recording??

+T for experimenting with Ipod and rockbox!
I'm curious to find out how much gain you're able to add? Does your rockbox recording scale go to +48dB just like on the Iriver? Or is there a different hardware limitation on the ipods? On Iriver, the golden rule is not to add more than +20dB or so, after that you enter the digital gain stage, so you might as well amplify that part in post.

Re. building a pre: Unless you're experienced, you'd be better off buying one.
Budget models are selling from $40, but the best value for money would be to ping Chris Church and ask if he has any used gear from his trade-in program:
http://taperssection.com/index.php/topic,119066.0.html

[Neilyboy]

good call sunjan I will probably do that. As for rockbox and the ipod. I will have to see. When I take my lunch break today I will run home and grab my 'tinkering' gear and bring it in here to run some tests. I will let ya know for sure. I do know it was letting me +gain up beyond 26db but I stopped there and backed it back down to like +22.5db while recording this particular sample. I will grab that stuff later today and get back with ya.

neil

[Church-Audio]

what type of epoxy do you suggest Chris. I purchased some stuff that was supposed to be flexible as well but the junk never set for me it just stayed like a liquid snot. It was just a one part epoxy nothing special (supposedly just a squirt and let dry product) (i would have to dig up the tube if i still have it, i may have thrown the stuff out by now, but want to say it was made by GE).

I think i picture in my head what you mean by using come copper foil. Would i slit a whole in it for the cable to go through then wrap it around the sides of the capsule?

Take care and thank you so much for your help as I do appreciate it!

Neil

Any 5 minute epoxy will work fine from a hobby store. As for the foil it comes in a roll you just cut a thin strip and "wrap" the capsule making sure only to contact the ground with the foil then you epoxy it into a brass tube.

[Neilyboy]

Thanks so much Chris. I will stop by the hobby shop tonight after work! Thanks again for your info it is much appreciated! Shoot me a pm if you have any old used pre's that you want to get rid of (for someone on a budget haha). Again thanks

Neil

[capnhook]

Hey guys, have you ever tried silver conductive epoxy?  We used to use something like this on complex EDM electrodes in the shop.....Put a ohmmeter on it ----- it's non-conductive to start, but as it sets up, you can see it become conductive as it hardens. 

"Use in place of traditional soldering on heat sensitive components. "

http://www.mgchemicals.com/products/8331.html

   Kevin

[Church-Audio]

Hey guys, have you ever tried silver conductive epoxy?  We used to use something like this on complex EDM electrodes in the shop.....Put a ohmmeter on it ----- it's non-conductive to start, but as it sets up, you can see it become conductive as it hardens. 

"Use in place of traditional soldering on heat sensitive components. "

http://www.mgchemicals.com/products/8331.html

   Kevin

Its ok for doing a few things now and then but its not something to rely on.

[capnhook]

Hey guys, have you ever tried silver conductive epoxy?  We used to use something like this on complex EDM electrodes in the shop.....Put a ohmmeter on it ----- it's non-conductive to start, but as it sets up, you can see it become conductive as it hardens. 

"Use in place of traditional soldering on heat sensitive components. "

http://www.mgchemicals.com/products/8331.html

   Kevin

Its ok for doing a few things now and then but its not something to rely on.

Yeah, most epoxies degrade over time when they take on moisture.

[Neilyboy]

very odd. I finally got around to bringing the mic's into work to play around with. I just sat the mics in front of my computer speakers and recorded two, one hour recordings. I was just playing some tunes through pandora. I listened to the recordings and from what I can tell the noise is completely gone and sounds great (I will have to burn them on a disc and listen on the drive home to be sure) but I think they sound alright today... I wonder just what in the heck was causing that noise to be picked up? That is just too odd. I will keep you posted on what I find.

Neil

[animuselanvital]

I second the cell phone problem.  In my computer room at home I have a 2.1 Blue sky media desk speaker setup through a focusrite saffire sound card box.  I never had any problems with them at any other time including with my particular cell phone.  Then one day I was working on a film fest project and I started getting this buzz type noise periodically throughout the weekend.  I finally correlated it to one of the actors cell phones when he had it laying out by my computer. . . about three or more feet away.  Every time that thing had an incoming call or text message I would get that buzzing noise exhibited through my monitoring speakers.  Thankfully I wasn't recording anything critical when it was going off!

[Neilyboy]

just wild.. I was just thinking back to that night. I went with my uncle and two of his friends from work. One being a gal who had one heck of a large purse. I had my 'gear' sitting on the same chair as her purse. I wonder if she had some goofy phone or device in there that was sending and receiving data. I am willing to bet that is what it was since I for the life of me can not replicate the problem. I have used my phone my work phone and anything else I can think of and nothing works haha. I would have to say at this point in time it was something in that gal's bag that was causing the goofy sounds that I heard throughout the night.

Neil

[Sunday Driver]

I had some cell phone interference in a recording one time. It happened twice at the beginning of the reocording, but only when I was actually pressing the button on the side of my R-09HR to adjust the gain. The guy sitting next to me was text messaging the whole time, but their was only interference when I pressed a button. My only reasoning is that somehow my touching the unit conducted the interference. Or maybe it was a pure coincidence.