[Flac] Replay-gain

Charles Velasquez velasquez at midland.edu
Tue Apr 15 09:26:10 PDT 2008


Thank you very much for the reply.  Hopefully if I get some time this weekend, I will re-rip a CD without the replay gain, this time making sure not to delete the wav files.  Then I will convert the flac files with replay gain back to wav and compare them to my re-rip wav files.  If they're the same, cool.  If not, I guess I will re-rip everything.  I don't know why I didn't think of this before. duh!

Charles Velasquez
Network Manager
Midland College
Pevehouse Admin. Bldg. #116
3600 N. Garfield
Midland, TX 79705   USA
Phone:  432.686.4824
Fax:  432.686.4206
velasquez at midland.edu


>>> Andrew Snare <ajs at pigpond.com> 4/15/2008 3:34 AM >>>
On Sun, Apr 13, 2008 at 02:10:51AM -0500, Charles Velasquez wrote:
> If that is the case, why is there a warning in the foobar2000
> converter dialogue box stating that "applying ReplayGain adjustment
> during conversion will irreversibly alter data in encoded file,
> unlike ReplayGain scan after encode"?

ReplayGain, as the name implies, works by calculating a scaling-factor
that should be used during playback. In flac the original audio
data is left unalterred; tags are used to store the ReplayGain
values.

I haven't used foobar200, but that message you're seeing implies
that if checked, the scaling-factor will be applied to the audio
data before it is encoded in the new format (mp3, in your case).
Hence the audio will be alterred and due to quantization (ie, rounding
errors) it is in the mathematical sense irreversible.

> I used EAC and AutoFLAC to rip my CD collection.  In the EAC
> command line options for flac.exe, I added the --replay-gain parameter
> and in the AutoFLAC setup, I enabled the "Add Replaygain" checkbox.
> I just downloaded foobar2000 and I can see that the replaygain
> values are there but after seeing that warning when converting my
> flac files to mp3, I became concerned.  I used AutoFLAC so that I
> can easily take my flac files and recreate the CD's if I ever needed
> to (can't get my folks to buy mp3/flac players yet and their CD's
> tend to get abused).  I want an exact copy of the original CD (as
> close as possible anyway).

> Seeing that warning above makes me think
> that since I applied replaygain to my flac files when creating them,
> that I no longer have an original rip.

This is probably incorrect. The audio data from the rip hasn't been
changed by calculating ReplayGain; merely a few extra tags were
added.

> If I convert the flac files (with replay gain values) back to wav
> files (autoflac does this for me), will these converted wav files
> be the same as the wav files created during my original rip of the
> CD?

Yes, so long as that conversion does not 'bake in' the ReplayGain
scaling.

> Do I need to rip my CD collection again without the replaygain
> so that I can use these to create a copy of the original CD if
> needed?

I doubt it.

Check out <http://en.wikipedia.org/wiki/Replay_Gain> for a better
understanding of how ReplayGain works. It shouldn't be necessary,
but might help you understand the various knobs you're seeing in
AutoFLAC, EAC and foobar2000.

Cheers,

 - Andrew



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