Removing Mobile/Cell Interference

I have started as a artist/band interviewer for a local street press mag and my new dictaphone interferes with the frequency of my mobile phone (a sharp buzzing noise is heard) when I record over the phone interviews. I was wondering if anyone knew of a technique using audacity to get rid of this unwanted sound???

A notch filter may remove it, e.g …

I think that’s incorrect. I think the cellphone is messing up the recorder. We have several editors whose cellphones drive us crazy. Every time they get a call, all the computer speakers in the office go nuts.


You need to separate the two or shield the recorder. As an experiment, wrap the recorder in aluminum foil and make a short recording.

If the interference is anything like what we get, you can’t take it out in post production.

Separation can be as simple as mount a cellphone holster to your leg just below the knee and continue to hand-hold the recorder. That may be enough. If you’re hand-holding them both that’s asking for trouble.


ahhh cheers
well this may be due to my own noobyness


This post is interesting, and could perhaps help me solve my novice problems in my recordings too.

Here’s what I’m trying to do:

I must record some phone interviews using a cellphone (on loud speaker mode). I’m using a hand-held digital voice recorder for that. So I have the cellphone on loud speaker on one hand, and the digital recorder on the other, with the mic pointing towards the speaker of the cellphone.

Now, what happens:

Everything runs smoothly during recording. I get no weird noises whatsoever. But when I go to listen to the recording, I get this “BRBRBRBRBRBR__tick_tick_tick_tick_ BRBRBRBRBRBRBRB” interference noise. It’s like the noise you hear when you have a cellphone near a computer and it rings, that you hear something like EMI noise.

I know cellphones are complicated in this sense, but unfortunately I must use them for the interviews.

So… any ideas of how should I proceed to have a better chance of not destroying my interviews?

cell phones play havoc with recording devices
other stuff too

you might find a cable that can connect them together
that is long enough so you can separate them to minimise the noise
but that would be a long cable
very long

our cell phones interfere real bad up to about 10 feet
with some noise as far as 30 feet

your best bet to record a phone call is to use a land line
and special equipment (not expensive) made to record calls

If you really need to record from a cellphone, then the best option is to use a cellphone that has a “record call” function built in. Otherwise, the better option is to record from a land line.

shouldnt be hard for some hacker
to tweak a phone to record a conversation

maybe its already been done
outside the cia

Thanks for all the answers.

Persisting with the cellphone as the device I’ll use, would you recommend wrapping the mic with alluminion foil and doing a hole in it to attempt to filter the EMI?

I noticed that in some parts of the interview I get a lot of noise, but in others (up to two full minutes) I get no noise at all. So I believe it is very sensible in relation to the distance between the two mediums, you know? As my hands got closer, perhaps I got more noise, but as they were farther apart it got much better - a matter of a few inches, not much. As nothing else was happening, I believe that the distance between them could be something to work out, since I got some nice pieces of recording among some parts in which noise appeared.

Antennas have magic properties in the Near Field – when you get very, very close.

See: Apple iPhone 4.

Did you ever describe what your recorder was and how you have it connected? Are you using the hands free setting on the phone and just leave the recorder running on the table?

I have a PearlCorder about the size of a candy bar cellphone and it would child’s play to wrap it in aluminum foil (except for the microphone) after starting and then make the call. Have the foil precut and ready to go.

I believe there are ways to connect the cellphone’s headset socket to an external recorder or cable system. I’m in deep water here. I know a lot more about antennas than I do cellphones. Once you do that, you can put the recorder a good distance away from the cellphone and if there’s still leakage, there are ways to treat the audio cable so it doesn’t pass radio interference.

So I’m still a little misty exactly how you’re doing the captures now and with what.

I would not recommend trying to record a land-line. The cheap recorders only capture one side of the conversation.


maybe a different recorder would be less noise prone

dont know about OPs recorder
a zoom H2 could use a mini-mini stereo connector
but the cell phone might have one of those TSSR connectors
then an adaptor is needed ala jupiter jack

which might be anotehr solution
use a jupiter jack in the phone
set fm radio far away with mini-mini link to H2 or similar

<<<I must record some phone interviews using a cellphone (on loud speaker mode). I’m using a hand-held digital voice recorder for that. So I have the cellphone on loud speaker on one hand, and the digital recorder on the other, with the mic pointing towards the speaker of the cellphone.>>>

There it is. I missed that earlier. So you can’t easily separate the two devices, but they’re antagonistic toward each other. If it’s obvious where the microphone is on your recorder, try the aluminum foil trick. You could make a little pouch and slide the recorder into it. You don’t have to go into full wrapping mode each time. You can get woven fabric with metal fibers in it and get someone to sew you a simple pouch. Many possibilities.

If the interference is right on the edge of being objectionable, the foil may make it vanish completely. Radio interference is serious magic and moving the two units an inch or two one way or the other may cure it completely. Just to underline the oddness of radio waves, they have a physical size or distance associated with them – officially “wavelength” and they travel through the air in bunches. You may find separation of five inches and ten inches is noisy (for example), but seven inches is clean. Fourteen is OK, too. Experiment.

And has been pointed out already, if your recorder happens to be exactly the right size top to bottom, it will make a good, efficient antenna. You can have very serious interference and it will be very difficult to remove. The size of the recorder is “friendly” to radio waves.

You may not need to jam the recorder right into the cell phone at full volume, either. That PearlCorder will record very nice voices from people speaking in normal voices across the room. Maybe not interview quality, but I can’t believe you’re getting interview quality anyway with the cellphone turned all the way up.


It doesn’t have to look like you raided the kitchen, either. Hollywood Grip suppliers will sell you black foil. They use it for lighting problems. Block intense stage light with something that’s malleable and not likely to catch fire.


Lead lined pouch ? ( designed to block x-rays) …

The lead compound used may not actually conduct electricity so I’m not sure if it will work to shield against RF.

BTW apparently thieves know about the aluminium foil trick: to shield the RFID tags in stolen goods from the sensors …

Most systems can be circumvented by placing the tagged goods in a bag lined with aluminum foil. The booster bag will act as a Faraday cage, shielding the tags from the antennas.

Slightly off-topic, but for another kitchen foil shielding application:


It may have the same effect but different technologies. Instead of suggesting strongly that radio waves go 'round (Faraday cage effect), lead absorbs them and turns them into heat. There is no doubt in my mind it would work. It doesn’t look like you raided the pantry, but you may have to figure out where to put the microphone.