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Folks,

If I'm looking to salvage as much audio quality as possible for music files while still reducing the overall file size and moderating the volume, is it better to appy gain reduction (eg: from 96.5db to 89.0db using MP3Gain) BEFORE or AFTER converting bitrates, (eg: from 256kbps to 160 kbps using Bonc Encoder)?
That is, will I get better sound if I convert the bitrates first or if I reduce the gain first??

Much obliged.

Kas

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if you're concerned about quality, don't convert bitrates. re-rip from CD and encode to your new bitrate. gain (in this sense) doesn't really enter into it. –  quack quixote Nov 30 '09 at 9:12

2 Answers 2

It shouldn't matter what order you apply these operations in. MP3gain performs its calculations and writes the result to APEv2 tags in the MP3 file, so the actual audio data isn't altered.

If you have a particularly braindead encoder, it may apply the gain change during decoding, in which case you'll end up transcoding the gain-altered audio data. (This would be a Bad Thing(tm).) You could use an audio editor program like Audacity to examine the waveforms directly to determine whether this is the case.

Most likely, transcoding will fail to copy all the metadata from the original to the re-encoded MP3, so you'd need to run MP3gain on the transcoded files anyway.

If you're really concerned with audio quality, don't transcode your files. Re-rip the CD into the bitrate you need -- or better yet, rip to or purchase as a lossless format like FLAC, and then encode MP3s to the bitrate you need.

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Also, the changes MP3Gain makes are completely lossless. There is no quality lost in the change because the program adjusts the mp3 file directly, without decoding and re-encoding.

Sounds like MP3Gain just adjusts the overall volume level in the mp3 without transcoding (didn't know you could do that) so I don't think it matters when you do the gain change.

Really though you should try an experiment with the gain before or after and trust your ears.

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mp3gain works by adding a metadata tag with the gain change. the mp3 player software takes that change and applies it to the decoded audio data before it's sent to the soundcard. that's what makes it a lossless change; it's not actually altering the mp3 stream. –  quack quixote Nov 30 '09 at 9:08

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