flac encoder clips poorly

[mixxxbot]

Reported by: ywwg
Date: 2021-02-10T17:00:53Z
Status: Fix Released
Importance: Low
Launchpad Issue: lp1915298
Attachments: [wave clipping](https://bugs.launchpad.net/bugs/1915298/+attachment/5462352/+files/wave clipping), [flac clipping](https://bugs.launchpad.net/bugs/1915298/+attachment/5462353/+files/flac clipping), [flac with clipping disabled](https://bugs.launchpad.net/bugs/1915298/+attachment/5462356/+files/flac with clipping disabled)

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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?

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:00:53Z
Attachments: [wave clipping](https://bugs.launchpad.net/mixxx/+bug/1915298/+attachment/5462352/+files/wave clipping)

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:01:11Z
Attachments: [flac clipping](https://bugs.launchpad.net/mixxx/+bug/1915298/+attachment/5462353/+files/flac clipping)

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:03:06Z

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this might be a bug in sndfile

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:08:12Z

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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.

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:14:47Z

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

[mixxxbot]

Commented by: Be-ing
Date: 2021-02-10T17:18:31Z

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Upstream bug in libsndfile, already fixed: libsndfile/libsndfile#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. #3615 will fix this for WIndows.

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:19:30Z
Attachments: [flac with clipping disabled](https://bugs.launchpad.net/mixxx/+bug/1915298/+attachment/5462356/+files/flac with clipping disabled)

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:19:59Z

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

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:21:02Z

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ubuntu 20.04 has 1.0.28-7

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T17:21:48Z

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thanks <3

[mixxxbot]

Commented by: ywwg
Date: 2021-02-10T18:06:51Z

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yup, updating to git sndfile fixes the issue

[mixxxbot]

Commented by: Be-ing
Date: 2021-03-08T20:38:42Z

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Fixed for Windows and macOS: #3615
Linux distros update at their own pace.

[mixxxbot]

Commented by: daschuer
Date: 2021-03-11T09:02:24Z

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The fix was done in this commit.
libsndfile/libsndfile@b9e5443
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

[mixxxbot]

Commented by: daschuer
Date: 2021-03-11T09:23:54Z

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

[mixxxbot]

Commented by: daschuer
Date: 2021-03-11T09:35:55Z

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

[mixxxbot]

Commented by: daschuer
Date: 2021-03-12T18:57:58Z

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#3697

[mixxxbot]

Issue closed with status Fix Released.