Fix: don't export loudness info to Engine #11979
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| // However, getting it wrong and accidentally scaling a waveform beyond a sensible maximum | ||
| // can result in no waveform being shown at all. In order to be safe, no loudness information | ||
| // is exported, resulting in waveforms being displayed as-is. | ||
| snapshot.average_loudness = 0; |
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Judging form t he variable name it needs to be_
| snapshot.average_loudness = 0; | |
| snapshot.average_loudness = 1/pTrack->getReplayGain().getRatio(); |
Because the ReplayGain value is used as extra gain to have all tracks with the same loudness.
This means for instance normalized track has an average loudness of -18 LUFS (on a dB scale)
The replay Gain will be 0 for this track.
If the same track has a doubled sample voltage it has an average loudness of -12 LUFS, and the replay gain will be 0.5.
Applied this, we are back to the desired -18 LUFS.
Then the question is: What is the scale of average_loudness. Is it a ratio or a dB value?
But does it mean compared to the ReplayGain2 LUFS?
Do you have a set of tracks where the average_loudness has been set before we have messed it up with Mixxx?
Maybe we can spot a rule how it compares the the Mixxx Replay Gain column.
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@daschuer This is indeed the purpose of upstream issue xsco/libdjinterop#103 - the exact meaning of average_loudness isn't currently clear.
In the past, I had made an assumption that ReplayGain ratio was a good fit, but Denon players use the value to scale the waveforms, and the bug being fixed here is that some bad values cause the waveform to be scaled out of range, at which point it is no longer rendered.
I've been working through more methodically with an analysis suite of tracks to try and determine the exact meaning of the fields in Engine format. When we have confidence in the true meaning of the fields, we can come back to Mixxx and set the value properly.
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@whanake-music confirmed this to be solving the issue. So lets merge and postpone further experiments to another PR.
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OK. |
Exporting the ReplayGain ratio to use as track loudness info on Engine exports could result in scalars that can cause rendering errors on hardware players.
This PR changes the export process to play it safe and not provide any track loudness info. Basic experimental testing shows that this does not cause any waveform-rendering regressions, but does fix tracks where the waveform was not previously displayed correctly. Furthermore, this change does not affect the outputted audio.