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I recorded some lectures with my smartphone mic and I was wondering is someone knows a good guide or has tips for cleaning up speech (not vocals in a song) with audacity.

The lecture is recorded via a smartphone on the desk so there are the following problems in decreasing importance:

  • low speech volume

  • few shattering noises from the table vibrating when someone hits it (I could probably dampen it in Hardware in the future)

  • pencil sound

  • people chatting in low voice in the vicinity

I am working with audacity, and the goal is to increase the subjective audio quality thus making it easier to listen to the lecture afterwards. The quality is already at a point where one can listen to the lecture, it is just quite exhausting.

I am aware that the audio quality will never reach a "good" level still I think that there are things that can be done.

So far I tried lowpass and highpass filtering but I somehow fail to set the right variables. The plethora of filtering options in audacity is also a bit overwhelming.

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2 Answers 2

This solution depends on what is the level of the background noise compared to the voice of the lecturer. If this ratio is high enough, you can try to apply gating effect. What it basically does is attenuate signals that register below the threshold, so at all times when your lecturer is silent, everything else will be silent as well. Then you can play a bit with attack/hold/release settings to make it sound reasonable.

But again, this solution is only applicable if the "noise" level (the things you want to remove) is significantly lower that your lecturer level. Otherwise, gate will silence both without making a distinction.

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You could go into Audacity and use Noise Removal. Select a section of chatter, preferably with no talking by the professor (between his breaths, maybe)? With your selection active, go through the effect tab until you find Noise Removal. Select it and click 'get noise profile'. Now, select all of your audio, go to Noise Removal again and click OK. It may distort the audio, but most chatter should be gone. You can repeat this step for the pencil tapping and the "shattering noises" if they happen a lot.

You can increase the volume of the audio by selecting all of it and clicking "Amplify..." under the effect tab. The default value when you click "Amplify..." sets it to 100% volume, but if this is quiet, then just make the audio louder by checking "allow clipping" and dragging the volume up until you're satisfied. (None of this really matters anymore though, because you're out of school, right?)

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