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bellamysprotege

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wav and mp3 compression - 2008/02/13 23:27 Ok..
(following a discussion with John over at Clique...)

has anyone noticed track length changes when converting wav files to mp3?
Basically, I sent John a wav file which was supposed to sync up to an mp3 file (indeed it does on my computer).. but when he tried it theres a problem with the sync, and the tracks end up out of sync by about 0.4 seconds...

I've tried this on my computer, converting a wav to mp3 and then loading them both into a sequencer, and would you believe it, they're out of sync as well! (although less ths time, around 0.01 seconds)

Has anyone else come across this? Its a completely new problem to me and I'm stumped!

ali

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Kemmler

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Re:wav and mp3 compression - 2008/02/13 23:38 I'm not sure exactly why but MP3s typically create a gap of silence (on the order of what you're talking about) in front of the waveform after encoding. The main way to get rid of it is to convert back to .wav and then use a utility to automatically trim, or just chop out the extra samples by hand. A pain in the butt to be sure.

Hope this helps.

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clique

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Re:wav and mp3 compression - 2008/02/13 23:53 The curious thing is that it's not a matter of overall track displacement (which might be explained by some extra silence at the beginning of the new file). There's a drift. The tracks start off in sync but end up out of sync.

The complete process, on my end, is as follows:

The potential weak link in that process is the conversion of the original WAV into an MP3, making an unreliable reference source. But I've never heard of this happening before.

Anyone else?

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bellamysprotege

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Re:wav and mp3 compression - 2008/02/14 00:00 The potential weak link in that process is the conversion of the original WAV into an MP3, making an unreliable reference source. But I've never heard of this happening before.

Y'know I think this is what it must be.. when i convert WAV2 into an mp3 and compare them, the mp3 is consistently out by however many samples all the way through which must be Kemmlers point (although to be honest I had never heard of this phenomenon...)

That wouldn't explain the 'drifting' though, its really starting to bug me now!

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mick

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Re:wav and mp3 compression - 2008/02/14 00:45 Very common. Try this sometime. Do a click track in your DAW. Spot on perfect. Export it, encode, decode, load it. You'll find the beats are out-of-sync at the end.

We're going to have to use FLAC or WAVs. I would suggest FLAC, it will halve the file sizes. IF you WAV->MP3->WAV the encoder is the man. With FLAC, music is the man.

Don't let the encoder be the man.

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Kemmler

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Re:wav and mp3 compression - 2008/02/14 00:51 Drifting could be caused by your decoder improperly handling VBR... but that is pure speculation. Not sure but my guess it's a decoding problem. Mick is right, much better to use FLACs.

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VUA

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Re:wav and mp3 compression - 2008/02/14 06:50

Post edited by: VUA, at: 2008/02/14 06:52

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clique

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Re:wav and mp3 compression - 2008/02/14 06:54 I encoded the MP3s with CBR, so hopefully VBR wouldn't be an issue.

In any case, I just stuck WAV files in ZIP files. I'm going to guess that the proliferation of broadband connections (or the patience for dial-up) when downloading these relatively big files would be more agreeable to a greater number of folks than encountering mysterious FLAC files. Just a guess.

Isn't the Internet amazing...

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