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I used to record important technical meetings and demos using Camtasia Studio, using a Mic to capture the speaker voice.

Sometimes we invite attendees by asking them to call us in the meeting, and they would call on a cell phone then we switch it to loudspeaker so we can hear and talk to them and also record the conversation on Camtasia.

The problem I am having now is that playing back those recording produces the regular noise that results from the microphone being close to the mobile phone (the kind of noise you hear when your mobile phone rings and it is near a speaker).

Any advice on removing this noise?

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migrated from stackoverflow.com Jul 15 '09 at 6:48

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6 Answers

You could use a filter on the recording. If I remember well, a low-pass filter should do the trick.

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try out something like:

audible (mac)

soundforge (pc) cool edit pro (pc)

the latter should do it real well. you will likely have to build a custom ex to cut out at certain frequencies to first locate, then isolate and reduce the noise. chances are good it will only be a few orders of magnitude better and not perfect, but it should get the job done.

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You definitely need some sort of software to filter out the noise. Some of the other answers here can address that.

If you're still doing the recordings and need to stop the cell phone interference, use ferrite beads near the base of each speaker.

By the way, just in case anyone is curious, these can be used for small desktop speakers, too.

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I haven't heard of ferrite beads before. Interesting. –  Sam Merrell Jul 15 '09 at 7:18
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Audacity would work great to edit out the noise from the cell phone. It has a filter that you can give it a sample of the noise you want to remove and then you can apply it to the recording to remove (as best as it can) the sound from the recording. You will have to probably try it several times to get it right, and it won't remove it completely, but it should help quite a bit.

Audacity also has several other filters and tools to help remove general noise from a recording which should help with the quality as well. Hope that helps.

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This is what I use without exception. You just select some noise, click Effects > Noise Removal, click "Get Noise Profile", then select the part you want to remove noise from, open the Noise Removal dialogue again, and click "Ok". Works perfectly every singe time. –  marcusw May 5 '10 at 17:46
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Just use ferrite beads on your wiring. Never solve a hardware problem in software if you can avoid it.

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Question RE ferrite beads: are they always active? Or do they only 'kick in' with bursts of HF? –  bobobobo Jul 21 '09 at 22:18
    
they're not active, since they don't actually do anything. They prevent interfere passively, by absorbing the HF noise, and converting it to heat (which is almost impossible to notice) –  Mikeage Jul 22 '09 at 11:04
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Bias soundsoap works great for removing this type of noise and even just lowering the regular noise floor that occurs with most recording devices. It comes both as a plug-in and as a stand alone application.

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protected by random Dec 15 '10 at 22:57

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