Re: [codec] OggOpus: Rational for excluding replaygain tags?

Calvin Walton <calvin.walton@kepstin.ca> Wed, 07 November 2012 22:51 UTC

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From: Calvin Walton <calvin.walton@kepstin.ca>
To: Gregory Maxwell <gmaxwell@juniper.net>
Date: Wed, 07 Nov 2012 17:51:36 -0500
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Subject: Re: [codec] OggOpus: Rational for excluding replaygain tags?
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On Wed, 2012-11-07 at 17:41 -0500, Calvin Walton wrote:
> On Wed, 2012-11-07 at 19:46 +0000, Gregory Maxwell wrote:
> > Calvin Walton [calvin.walton@kepstin.ca] wrote:
> > > While I don't see any technical problems with R128 - it is a good volume
> > > normalization scheme - the issue is that it is a *different*
> > > normalization scheme from the replaygain tags that are supported in
> > 
> > Replay gain does not specify a method for measuring the level. The
> > R128 measurement technique is, in fact, being used in place of te
> > older replay-gain in many places and I wouldn't be surprised if it
> > were actually the most popular of the two then.   With that in mind
> > the only difference between the two values is the specified meaning
> > and a constant scaling factor for the different reference levels.   So
> > it's trivial to make software that that can play a mixture of OggOpus
> > and replaygain vorbis with the expected constant levels.
> 
> Hmm? Replaygain does specify a method. They go into a lot of details on
> http://www.replaygain.org/ to describe the loudness filter used, the
> method for calculating RMS power levels afterwards, the histogram-based
> statistical processing, and how to calibrate the gain level to the -83dB
> reference with a pink noise signal.

Sorry, a minor correction - and this *is* something that has caused
interoperability issues in the past: The correct replaygain reference
gain level is "89 dB" SMPTE SPL, not 83 dB. (The - sign was a typo...)

-- 
Calvin Walton <calvin.walton@kepstin.ca>