GSM noise from cellphones while using Zoom 4

Posted: Thu Aug 14, 2008 11:53 am

A friend just sent me a disc from a live recording he made over the weekend using his Zoom 4 hand-held recorder. Several times during the performance there was a serious interference problem from people nearby who were using GSM cell phones (AT&T, T-Mobile, etc). Even though their phones were turned to silent they were still powered on and whenever they had an incoming signal it created a powerful series of pulses (217 Hz with a 12.5% duty cycle). CDMA cell phones (Verizon, Sprint, etc.) do not seem to exhibit this problem.

Have any of you encountered this same difficulty and if so how did you deal with it. My friend was using the mics that were built-in to the Zoom 4. I don't know whether or not using external mics on the balanced XLR inputs would make any difference. I could not give any recommendation since I have not experienced this personally.

Posted: Thu Aug 14, 2008 1:30 pm

Yeah, isn't it amazing! The FCC used to prevent problems like this. It's a huge problem! I've heard this cellphone noise come blaring through rock-and-roll PA systems! Nothings going to stop it. And you can't get rid of it after you recorded it. If you ever figure out how, let me know? Yeah, and its AT&T which was formerly Cingular, which was formerly AT&T. Maybe when true digital microphones are invented, this will be a thing of the past? There is no true digital microphones but analog microphones with digital converters.

OK so the FBI has laser microphones.
Ms. Remy Ann David

Posted: Thu Aug 14, 2008 2:10 pm

To record lasers with?

Can't you notch filter at 217Hz to remove the worst of it? I had a problem with ringing at around 480 Hz from a vocal recording, a bit of EQing made it miles better than before.

Posted: Thu Aug 14, 2008 3:19 pm

We're talking about the pulsating noise that occurs when a cellphone receives signal from and during an incomming call. The noise actually has quite a broad bandwidth and will probably interfere with a good chunk of your mix if you try to eq it out. Personally, I think it's a lost cause but hopefully someone else will prove me wrong.

Posted: Thu Aug 14, 2008 10:01 pm

Mmmm. The more I think about it the more it sounds ridiculous.

In my case I had a ringing at a single predominant frequency which only happened when the speaker was talking.
This ofc, is totally different.

Posted: Thu Aug 14, 2008 10:26 pm

Yes, and to compound the problem.. when you tell people to turn their cellphones off, they put them on vibrate.

Posted: Mon Sep 08, 2008 5:19 am

Quality gear doesn't really exhibit this problem. Both Schoeps and Neumann have modified their mic circuits to all but eliminate it. Cheap unshielded recorders are another problem.

Because the Zoom mic pres are in that little unshielded plastic box its going to be impossible to solve.

Posted: Mon Sep 08, 2008 7:21 am

DavidSpearritt wrote:

Because the Zoom mic pres are in that little unshielded plastic box its going to be impossible to solve.

Try wrapping the box in tin foil. It keeps the aliens from reading my brain waves, so it should keep the RF signal out.

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