Microphone picking up GSM signal :-/

[yetanotherlogin]

Hello

In this sample, we can hear the signal of someone's GSM cellphone.

The sound was recorded using the embedded camcorder microphone, but I had the same issue with an independent digital audio recorder.

Is there a way to protect digital recorders from picking up cellphone signals?

It's an especially big issue when recording indoor, since the lower the signal from the wireless network, the stronger the cellphones try to connect.

Thank you.

[Richard_G]

Switch your phone off then. It will have to be very close to the camcorder so is likely to be yours or somebody very close to you.

All I get in the sample is a couple of advertising videos with no interference on the sound.

[pandy]

Yes, you can use RF absorbing/shielding materials however it is easier to switch off phone as Richard G advise.

http://www.hollandshielding.com/214-Electrical_conductive_tapes_and_foil_selection-en.htm
http://www.hollandshielding.com/138-Thermally_Conductive_Microwave_Absorber_Pad_ferrite_tiles-en.htm

http://www.devicetech.com/products-emi-rfi-shielding-thermal-management/shield-fast-rf...rber-materials
http://solutions.3m.com/wps/portal/3M/en_US/AdhesivesForElectronics/Home/Products/EMIE...C/EMIAbsorber/

[yetanotherlogin]

Switch your phone off then. It will have to be very close to the camcorder so is likely to be yours or somebody very close to you.

Mine was switched, and I can't force ten's of people in the room to switch theirs off entirely (not mute) simply because I'm recording.

Yes, you can use RF absorbing/shielding materials however it is easier to switch off phone as Richard G advise.

Thanks, I'll investigate RF shielding.

[pandy]

Yes, you can use RF absorbing/shielding materials however it is easier to switch off phone as Richard G advise.

Thanks, I'll investigate RF shielding.

Not sure what microphone we talking about but perhaps problem is related to way how particular device was designed - then only complete shielding can help, easiest way is to place recorder in some Faraday shielding bag.

http://www.amazon.com/Black-Hole-Faraday-Bag-Isolation/dp/B0091WILY0

Personally my self - i placing few times cable trough http://intermark-usa.com/products/emc/emi-ferrite-emi-ferrite-cores/ (ferrite split/clamp cores) this work quite fine for most RF interferences even from strong local RF sources like cell phones

http://audiosystemsgroup.com/SAC0305Ferrites.pdf

But this can be not possible (probably) in your case thus need to use something more fancy (and expensive).

[yetanotherlogin]

The video was shot using the embedded microphone in the camcorder, and the problem also occurs with a digital audio recorder also with its embedded microphones (Tascam DR-40), so I can't use a ferret.

Thanks for the link on that Faraday shielding bag. I could use something flexible to wrap around the device.

[pandy]

Usually fancy bags use Welcro to seal bag but you can use fine metal mesh fabric - it should work exactly the same, or even normal baking aluminum foil - just make small (1 - 2mm) hole where mic is located after wrapping recorder (you lose display and direct access to switches ) - this should work fine - obviously this method is valid only for audio recorder.

[yetanotherlogin]

I'll try to find that kind of bag over in stores over here so I can try it and see if it works. Otherwise, I'll play with aluminum foil. Thank you.

[Cornucopia]

Take 2 metal colanders, put your audio recorder in the basin of one, hit record, invert the other colander and place on top, tape the rims together to "seal shut". If it works, great! If not, you're only out a few bucks but can now make LOTS of pasta!

Scott

BTW, there actually is some science to this. Similar to faraday cage, as long as the metal is conducting (couldn't use aluminum, though, which is the most common).

[yetanotherlogin]

Thanks for the idea. But while fine-grained colanders should not be an issue for audio recorders, they won't do when using a camcorder

[pandy]

Thanks for the idea. But while fine-grained colanders should not be an issue for audio recorders, they won't do when using a camcorder

This is why they produce this:

http://www.hollandshielding.com/226-Transparent_foil-en.htm

http://www.hollandshielding.com/115-Mesh_foil-en.htm

Perhaps cell phone jammer can solve your problem? (please check local law for legality)

[yetanotherlogin]

Thanks for the links. I assume professional-grade cameras are immune to this because they have no embedded microphones and rely on XLR microphones instead.

I thought about cell phone jammers, but they are illegal, and the portable ones apparently don't work too well.

[Cornucopia]

1) No camera, microphone or recorder combination is totally immune. That's why pros use balanced (xlr) mikes & cables, position for best snr, and rely on double system, and also why they/we get pushy & demanding that no live phones be allowed on set during certain times. That is sometimes the only way to have full isolation.

2) Your best quality option is probably also your cheapest - get pro, balanced, xlr mikes and use the separate audio recorder (aka double system). And position the mikes better (rarely is at-the-camera an optimal choice).

Scott

[bigass]

I remember the first time I used a 'digital' cell phone -- a Sony PCS model in the mid-to-late 90s -- near one of the old Sony portable news tape decks... and it induced a wicked buzz in the playback speaker. Then we started getting that interference from Blackberry pagers & handsets when they were transmitting.

Really, using balanced audio, meaning XLR, is your second-best option. Best option is just to turn off equipment that would interfere with recording. At the very least, keep it far away from your gear.

Sometimes, in audio/video, we have to do what's best for the product, and not best for the producer. That may mean closing the blinds to avoid a clash of color temperatures. It often means shutting off the air conditioning to get a silent room. Sometimes we work under a horse blanket in lieu of a voiceover booth. Going without a cell phone for a short while may just be the price of doing business, if you can't afford the price of doing business with different gear.

[yetanotherlogin]

Thanks much for the infos. I shoot in crows (conferences) so cell phones will always be part of the landscape. But as it's not for professional use, I'll just live with the occasional GSM interferences.

[Cornucopia]

But you'd cut down ALOT of the problem by going to Balanced/XLR mikes & cabling...

Scott

[yetanotherlogin]

That's what I was thinking of doing. I'll see if I can find good, affordable XLR microphones to hook up to the Tascam DR-40.