flac encoder clips poorly

[Owen Williams]

I recorded a set and there was some clipping, but it didn't sound bad out of my speakers. However the recorded flac has awful popping noises wherever the clipping happens. I did some testing and discovered that it clips incorrectly. If I record with WAVE, clipping looks like you'd expect (first image). But in flac, the clipped value bounces from 0 to 1 crazily (second image). I wonder if this is an issue with going from float to int?

[Owen Williams (ywwg)]

this might be a bug in sndfile

[Owen Williams (ywwg)]

According to our code:

// Tell the encoder that, when converting to integer formats, clip
    // automatically the values that go outside of the allowed range.
    // Warning! Depending on how libsndfile is compiled autoclip may not work.
    // Ensure CPU_CLIPS_NEGATIVE and CPU_CLIPS_POSITIVE is setup properly in the build.

So this may be a case where the ubuntu-built sndfile is not compiled correctly. I am trying disabling clipping to see what happens.

[Owen Williams (ywwg)]

Setting it to false appears to fix the issue, I'll make a PR and we should have people test it.

[Be (be.ing)]

Upstream bug in libsndfile, already fixed: https://github.com/libsndfile/libsndfile/issues/309
libsndfile was practically unmaintained for a while so there was not a release with this fix until recently and Linux distros may still be shipping old libsndfile versions. 1.0.29 was the first version with the fix. https://github.com/mixxxdj/mixxx/pull/3615 will fix this for WIndows.

[Owen Williams (ywwg)]

oh cool thanks. yeah playing with the setting did not help. In the interim, using WAV output is a lot better

[Owen Williams (ywwg)]

ubuntu 20.04 has 1.0.28-7

[Owen Williams (ywwg)]

thanks <3

[Owen Williams (ywwg)]

yup, updating to git sndfile fixes the issue

[Be (be.ing)]

Fixed for Windows and macOS: https://github.com/mixxxdj/mixxx/pull/3615
Linux distros update at their own pace.

[Daniel Schürmann (daschuer)]

The fix was done in this commit.
https://github.com/libsndfile/libsndfile/commit/b9e544328e423ac01cac14436b41942e27b6b5aa
part of v1.0.29

Ubuntu Bionic LTS has 1.0.28-4ubuntu0.18.04.1
Ubuntu Focal LTS has 1.0.28-7
Ubuntu Groovy has 1.0.28-8
Ubuntu Hisure has 1.0.31-1ubuntu1

Fedora 33 has 1.0.31

https://repology.org/project/libsndfile/versions

[Daniel Schürmann (daschuer)]

I cannot confirm that the issue is fixed after upgrade, because we don't set
SFC_SET_CLIPPING for flac.

[Daniel Schürmann (daschuer)]

Oh, we do set it.. strange, something else must be wrong.

[Daniel Schürmann (daschuer)]

https://github.com/mixxxdj/mixxx/pull/3697

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10318