Cleaning up audio

[renob123]

I was wondering what program you guys use to clean up the audio in an .avi. I usually use the Radium MP3 codec, and sometimes I have audio with a really high pitch squeeling in the background. Any ideas of a filter or something that'll get rid of it?

[mikecito]

You could pass the audio through Premiere or Cool Edit 2000 and use a high pass filter. It should get rid of the high pitched squeal, but it will also soften your high frequency sound - so it's a tradeoff.

[Alestrix]

@mikecito:
'I guess you mean a lowpass-filter :-) (passing below a certain freq, blocking above)

@renob123:
Using lame with the --lowpass option should do the trick and is probably faster than using CoolEdit.

[mikecito]

Yeah - thanks for the correction. I always get those confused anyway. :)

[renob123]

Alestrix: Where can I get "lame"? I've never heard of that program before.

[renob123]

Sorry, thought lame was an acronym for a second, I found it as soon as I looked for "lame". Will I have to separate the audio from the video in order to lowpass it, or is there some trick that will let me just do it without having to separate? Also, what frequency would be good? I can do x-overs with cars, but I don't know how to handle khz.

[Slogra]

Don't use radium codec :D

I used it long ago and the quality was really crap.

[Alestrix]

Originally posted by renob123
Will I have to separate the audio from the video in order to lowpass it, or is there some trick that will let me just do it without having to separate?

If you already have an AVI you will have to seperate (=demultiplex or "demux") the audio from the video (use search to find out how, there has been discussion about this in this forum).

If you just want to lowpass the audio after demuxing, you might use something like
lame --nspsytune --nssafejoint --lowpass 14 --alt-preset 100 --resample 44.1 <infile> <outfile>

The 14 after lowpass is just a suggestion and depends on the actual sound of your source. (So does the bitrate 100 - there's no point in using a higher bitrate than used in the original) The resample is needed to keep the sampling rate at 44.1kHz since lame resamples the audio to lower sampling rates when used with low bitrates. You might have to adjust the value 44.1 to be the same as your source.

If you demux with nandub or virtualdub and end up with an MP3 that has a WAV extension, you should also add the --mp3input switch.

Originally posted by renob123
Also, what frequency would be good? I can do x-overs with cars, but I don't know how to handle khz.
I used 14kHz in the example but I actually have no idea what might be a good value. Lower frequencies will sound "phone-lineish", higher freq might keep the high ringing of the original.

If you want to do more cleanup than just lowpass, mikecito's suggestion of using CoolEdit (or Soundforge) might be a good idea since those programs are capable of really neat "fixing". After that you can reencode the audio with lame (or if you want, oggenc to create a vorbis-audio file)
Finally mux the audio into the video again (look at the guides on how to do this) and everything's peachy :D

Whether all this is actually worth the hassle is a second thing.

One other thought crossed my mind: You can use a player with integrated equalizer and reduce the high frequencies on playback. Maybe there's a DirectShowFilter for this, dunno.

- A

PS: I'D like to be able to to that x-over stuff, too :)