Hi,
sox is your friend. It can be used to do pretty much all of this.
When I've done this, I've recorded the audio in at 44.1kHz 16-bit stereo,
then resampled down to 22.05kHz to halve the speed. If your device has
some aliasing when playing 22.05kHz material, you could always use sox to
resample back up to 44.1kHz, but use the resample effect or something else
more complex, not the simple rate conversion as it will leave these
aliasing effects in place.
But I'm getting ahead of myself.
First, the side-splitting. there's a few ways you can do this:
1. Use the avg or pick effects in sox. The version of sox you have will
determine which of these effects actually works for you. I've had problems
with both in various versions of sox, so have an experiment, but one of
them should work.
2. Alternatively, if you use ALSA, I know that arecord used at least to
have a feature where you could record the left in one channel and the right
in the other. hmmmm ok the help doesn't mention it, but it's the -I
option. Though it appears to only record in raw data, not as a wav file.
Still, sox could fix that if you wanted.
Having done that, you can use the reverse effect on the backwards files:
sox side3.wav side3forward.wav reverse
sox side4.wav side4forward.wav reverse
For trimming, I usually use soundgrab to edit manually, but you may be able
to get Sox's trim effect to work for you.
To halve the speed, you use one of the resampling methods. In my
experience, the quick and dirty rate effect is good enough for halving the
rate from 44.1kHz to 22.05kHz, but you should test it for yourself:
sox -r 22050 side1.wav side1slower.wav rate
or\
sox -r 22050 side2.wav side2slower.wav resample
There's about 4 different resample effects, check out the sox manpage for
the lowdown on all of them.
I usually also normalise so that I can set my levels at a safe level and
can have the files as loud as they can be without distorting. Best to do
this as your last step so that other effects don't cause the audio to
distort.
Example:
sox side1slower.wav -e stat -v
sox -v <output of previous comand> side1slower.wav side1louder.wav
1.0 is as loud as it can go, so if it's at 1.0 already, there's no point
and it may have in fact distorted somewhere.
Got no thoughts about detecting tones etc, I'd be interested to know if
anyone else has any.
For actually slicing up files, I've not used it, but qwavcut from the
Quelcomm tools may help if you can get something to detect these tones.
They're useful programmes to have anyway, I use qwavinfo and qwavjoin
regularly. qwavsilence may also help you:
http://www.etse.urv.es/~dmanye/quelcom/quelcom.html
Hope this all helps.
Geoff.
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