If the two files are both mono and you want to make them stereo then
judicious sample insertion will probably work reasonably well. If they are
both stereo then you need to look further into resampling since you may not
be able to insert samples at the same point in each of the respective
channels, and excessive insertion into one channel will introduce skew into
an otherwise synchronous pair of channels.
What is the format of the files? Raw audio, WAV, etc? What is the rough
content - if the signal is constant than sample insertion is not easy since
you may not have periods of silence. If the signal does have silent periods
then the solution may be a noise gate that inserts samples - this would be
all but inaudible. There is no reason why this should not work from file to
file with 'cat oldfile | <program> > newfile so should not need to have the
lot in memory.
Have you mailed the LAD list - somebody might be happy to bolt something
together for you, its not actually a lot of work for mono tracks.
Regards.
From: "Alex Polite" <notmyprivateemail@xxxxxxxxx>
Reply-To: A list for linux audio users
<linux-audio-user@xxxxxxxxxxxxxxxxxx>
To: "A list for linux audio users" <linux-audio-user@xxxxxxxxxxxxxxxxxx>
Subject: Stretching with very high accuracy
Date: Thu, 8 Jun 2006 17:39:48 +0200
Hi there.
I'm developing a little tool to automatically sync two audio
recordings of the same event made with two different recorders. I've
got the algorithms worked out and can correctly compute the drift and
offset between the files in my test recording. The next step is to
pad, stretch and mix the two files into one perfectly synced stereo
file.
The drift is very small. In my test recording the drift is only 53
milliseconds over the course of an hour. My stretch factor is
0.99998525762821
I've tried to stretch the file with sox:
sox infile.wav outfile.wav stretch 0.99998525762821
When I try to line up the files in a ardour I realise that the stretch
sox makes is hugely inaccurate.
For testing purposes I tried to stretch an hourly long file (44.1kHz)
by some 2000 samples, but the resulting file was some 30000 samples
longer. The stretch was off by more than 0.5 seconds!
Is there anything I can do to increase the accuracy of sox? Is there
any other tool out there that will do a better job at stretching with
very high accuracy?
alex
--
Alex Polite
http://flosspick.org - finding the right open source
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