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[bspachman]

Perhaps I'm being naive, but I'm going through and redoing the audio analysis on my entire music library this weekend (25000+ tracks) and have discovered something I think is odd.

The main playback portion of my library is APE/APL files for my home stereo system. I also maintain a parallel set of tracks that have been transcoded into AAC files for use on my iPod.

I've noticed as the analysis has progressed that the replay gain, intensities, peak level, and BPM values as calculated by the analysis engine are different for the APE/APL and the AAC version of the same song...

Usually they are substantially different...not even close!

Can anyone explain if I'm just going to have to reanalyze the songs again (or come up with a more efficient way to copy the values?)

brad

[Matt]

If the replay gain is different between APE and AAC, it means the AAC encoder or decoder is applying a gain or loss, since the APE encoder and decoder are bit-perfect.

Normally the whole point of a good lossy codec is that the decoded signal strongly resembles the original.  You might try to make an MP3 with MC's MP3 encoder (which is known to be of high quality) to see if it more closely resembles the original than the AAC.

[bspachman]

Yah...clearly this isn't an exact science!...

The AAC encoder I used is the iTunes encoder (from whatever the current version is.. 7.3.2?). I invoked it as an external encoder from foobar2k using the helper application 'iTunes Encode'.

(FWIW, I've always had trouble using this external encoder from within MC--tags just aren't copied over properly. I didn't even try with MC12--have things improved?)

Regardless, performing audio analysis on the transcoded tracks generally gives a different intensity (with the APE/APL being a lower value); a different BPM (all over the place--sometime similiar, sometimes a multiple, sometimes just a couple of beats off); and different Replay Gain (generally the the APE/APL is less negative).

The real oddity to me is that the Album Gain is the same no matter which filetype is selected...

brad