[FFmpeg-trac] #9352(avfilter:new): loudnorm filter goofs loudness measurements in some cases

FFmpeg trac at avcodec.org
Fri Jul 30 06:47:23 EEST 2021

#9352: loudnorm filter goofs loudness measurements in some cases
             Reporter:  Gregory      |                    Owner:  (none)
  Beauregard                         |
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:  avfilter
              Version:  git-master   |               Resolution:
             Keywords:  loudnorm     |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
Changes (by kepstin):

 * keywords:  loudnorm,ebur128 => loudnorm


 Note that the test with ebur128 filter with different sample rates
 requires ffmpeg with commit 274112c88d89d839a27c0766f558f065f9eee0d7 -
 prior to that it used fixed filter coefficients and only worked at 48kHz.

 Given the difference between the 48kHz and 192kHz calculations, my guess
 is that one of the following things might be the problem?

 * The calculation of the K-weighting filter coefficients at 192kHz is
 incorrect, or
 * The resampling of audio from 48kHz to 192kHz is increasing the power of
 inaudible high frequency signals (which contribute towards the loudness
 calculation - it doesn't use a lowpass)

 The latter doesn't *seem* likely, but shouldn't be hard to rule out with a
 spectrogram just to be sure.
Ticket URL: <https://trac.ffmpeg.org/ticket/9352#comment:13>
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