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I want to add and crossfade multiple mp3s into a long mix.

Is there software that can mix many mp3's without re-encoding?

If i use a normal mixing program and decode-re-incode, how much worse is the sound?

If i encode a 256 color bitmap twice, it doesnt get worse, but if i encode a jpg twice it loses detail. i figure the same is true from mp3.

  • I'm not sure I understand what you mean by "losslessly in MP3 format", since MP3 is a lossy compression. – Andrew T. Apr 21 '15 at 13:41
  • Thanks, I re-worded the question accordingly. I mean without losses of fidelity from the DSP processing involved with mixing two mp3 files. – com.prehensible Apr 21 '15 at 19:30
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There are programs that can split and concatenate MP3s without re-encoding. So one thing you could do is to split a few seconds off every MP3 at the beginning and end, apply your cross-fades to them (with re-encoding), and then concatenate everything.

Regarding "how much worse" with re-encoding: If you choose a high bitrate for re-encoding, it shouldn't be noticeable. I don't know what will happen if the original bitrate is low and you choose the same low bitrate.

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To my knowledge, this is not possible. To add and crossfade audio data requires to decode the mp3 binary stream to pcm, then re-encode to mp3 the resulting pcm stream if you want an mp3 output.

As mp3 is not very good at cascading, you will (probably) have degradation, the overall degradation will depend on the input and output mp3 bitrate.

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