General Question

wildpotato's avatar

Is there a way to delete the sound of my typing from an audio recording of a lecture?

Asked by wildpotato (15121points) September 1st, 2009

I’m on Mac OS X Leopard; recording using Garageband or Microsoft Word 2008. I can make out the prof’s words on the recording just fine, but the tapping noise of my simultaneous note-taking is really annoying. Is there any way to selectively delete this sound, but leave the voice of the prof and other people intact?

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7 Answers

PerryDolia's avatar

Theoretically, yes.

Practically speaking, for the normal human? No.

You can reduce the sound of the keyboard a little through the use of a notch filter, but it won’t really make much difference.


wildpotato's avatar

@PerryDolia Hm. Can you tell me about how to use a notch filter on my recording, or point me at some software or codecs that can get it done? The tapping does sound a bit like feedback, and if notch filters are usually used for the purpose of eliminating feedback, then it seems like that might work OK. I’m not a computer whiz, can’t program or anything, but give me a set of basic instructions and a link to a site that kind of explains things and I can usually figure it out.

I find it a bit surprising that the Office folks didn’t anticipate this problem (seeing as they offer the recording option on the Notes template) and build something to counter the tapping into the program in the first place. Unless this is pretty much impossible, as you said…

Maybe a better question to ask is whether there’s a way to soften the sound of my keys, other than by putting a towel over my hands as I type.

PerryDolia's avatar

@wildpotato Even though, when we listen to a recording, we can easily tell the voice of the professor from the clicking of the keys, it is very difficult to remove a specific sound from the recording and leave the rest. This is because, to the the computer or software, the sound is just one big wash of sound, no individual parts.

So, we have to find a way to remove the part we don’t want even thought it cannot be easily identified.

I said “theoretically” in my answer, because, theoretically, you can invert the waveform of the sound of a a key and add it in on top of the original waveform and cancel the sound of the key. But practically speaking, this is way too difficult to do, one key tap at a time, even if you could invert the waves, etc.

The best you can do with normal equipment, is find the frequency of the sound of the key and remove that frequency. It is really a range of frequencies, and the more frequencies you remove, the weirder the remainder sounds, kind of like being underwater, if taken to the extreme.

You can use a program like Soundforge to create a notch filter, a filter that removes a narrow frequency of sound, and play with removing different frequencies to see how well you can dampen the key sounds. Its not easy, but you might be able to reduce them by half with some work.

Good luck.

wildpotato's avatar

@PerryDolia That makes sense, let me see if I get this right – every key tap would have a different waveform, so unless you tackle each tap separately, it wouldn’t work well. The other option, deleting the range of frequencies for all the keys tapping, would overlap onto the sounds of the things I want to keep, deeting parts of their waveforms and thus distorting them.

Oh well. Guess I’ll probably just live with it. Thanks!

PerryDolia's avatar

@wildpotato Sorry, but you got it.

zina's avatar

You could try a filter for a certain pitch-range, if you can identify where that is, as @PerryDolia said. I haven’t tried it in this exact situation, but quite successfully in others – the problem is that it usually works best when the frequencies you want and those you don’t want are far apart, but I’m guessing these are on top of each other. However, maybe reducing some high frequencies won’t much affect the sound of the voices but will take an annoying ‘edge’ off the key sounds. Which is better than nothing.

I don’t see a way to do it in GarageBand, and I don’t have the Word program. However you can do it in a rough way in Audacity, which is a free program you can download online. I wouldn’t be surprised if other free/open-source programs also have this capacity, and less expensive programs (Logic, etc) leading up to ProTools all do (in a more precise way).

Good luck!

zina's avatar

(oops, I posted my answer before the two above appeared – so it’s a little redundant!)

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