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level matching when comparing lossy to lossless
2Bdecided
post Feb 8 2013, 17:56
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ReplayGain developer


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It's made me realise that I ought to do a table with two columns, comparing ReplayGain and R128 step-by-step.

But I think I'll wait until someone who has actually coded R128 confirms my understanding of it.

The big differences are the different filter, the different block sizes + overlapping, and most importantly the -10dB gate + all-sample RMS of R128 vs just taking the 95th percentile RMS in ReplayGain.

The original reference levels are only a fraction of a dB out (-23LUFS is about 83.3dB SPL); ReplayGain was raised to 89dB, which, interestingly, is within about 1dB of SoundCheck.

To put it another way, you need a filter, you need some blocks, you need to add the results for each channel together, you need a dB scale, you need to ignore the quieter blocks, and you need to use a reference level of about 83dB (-20dBFS RMS, -23LUFS) to cover everything, or 89dB (-14dBFS RMS, -17LUFS) to cover mostly pop music.

It all ties in very nicely. Or to put it another way, different people "independently" came to almost the same conclusions.

Cheers,
David.

EDIT: Sorry for going further off topic. Just wanted to record this somewhere having worked it all out.

This post has been edited by 2Bdecided: Feb 8 2013, 17:56
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lvqcl
post Feb 8 2013, 23:19
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QUOTE (krabapple @ Feb 7 2013, 23:28) *
QUOTE (Garf @ Feb 7 2013, 14:03) *
If they're encoded from the same source I see no reason to level match, *if* the encoder is not intentionally changing the volume. I understand LAME does this at least in some ABR modes to lower the amount of clipping.

1dB of ReplayGain difference between lossy and lossless is surprising. The ReplayGain calculation isn't perfect of course, but that's more than I'd have expected. Are you sure the same ReplayGain *algorithm* was used in both cases? (original ReplayGain vs R128?)



Absolutely sure -- this was all done today, right before I posted, using Foobar's v1.2.2's replaygain scanner. The lame.exe is 3.98r that comes bundled with dbpoweramp (lame --license shows it as 3.98.4)

Perhaps others could try and see what they get? The track, btw, was 'Black Cow' , the first track on Steely Dan's Aja -- couldn't tell you exactly which CD version this is, I bought it many years ago.


All right, I found this track. Its track gain value is +0.10 dB (calculated using the latest foobar2000).

"Scan per-file track gain" command scans only files without RG tags. Probably your lossless file was already scanned using old RG algorithm.

This post has been edited by lvqcl: Feb 8 2013, 23:29
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