[pulseaudio-tickets] [Bug 87202] New: Strong noise (unintelligible) when playing through the analog output using mmap

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87202

            Bug ID: 87202
           Summary: Strong noise (unintelligible) when playing through the
                    analog output using mmap
           Product: PulseAudio
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: alsa
          Assignee: pulseaudio-bugs at lists.freedesktop.org
          Reporter: msanchez at gnome.org
        QA Contact: pulseaudio-bugs at lists.freedesktop.org
                CC: david.henningsson at canonical.com,
                    lennart at poettering.net

Created attachment 110686
  --> https://bugs.freedesktop.org/attachment.cgi?id=110686&action=edit
Output of alsa-info.sh

In the last few days I've observed the following issue in a Gigabyte BXBT-2807
unit[1] I have using a 5.0-2 release of pulse audio (from debian), but today I
could reproduce it as well with the latest code from the master branch, so
reporting:

STEPS TO REPRODUCE:

1. Get a GB-BXBT-2807 device or similar. This computer has the analog and HDMI
outputs in the same card and a combined Headset+Mic 3.5mm is the only way to
use the analog one (not sure if that causes the issue, though)

2. Connect your headphones to the 3.5mm, select them as output device and play
some music through them

3. Now repeat one of the following actions several times (or both combined)

  3.a Change the volume up and down continuously (e.g. from 100% to 0% and
back, x10-20 times)

  3.b If you have the HDMI cable connected, open gnome-control-center and
switch back and forth between the HDMI and the Headphones outputs


EXPECTED OUTCOME:

Repeating (3.a) or (3.b) many times should not result on hearing any noise
being heard, just in the volume levels or the output device changing,
respectively.


ACTUAL OUTCOME:

Eventually, after repeating 3.a or 3.b (or a combination or both) for a few
times, the sound changes into a very weird noise that can or can not resemble
the original song being played. Once that happens, you need to either restart
pulseaudio or unplug + re-plug the headphones to get back to normal (and even
doing that, sometimes you might need to try that "reset sequence" more than
once).

I've recorded a video to explain the problem even better:
https://www.youtube.com/watch?v=7qwAdtXtbq8&list=UUtP76gwwFTMmUp8NBhA0FVA 


ADDITIONAL INFORMATION:

Note 1: By hooking some code in mmap_write() I managed to dump to a file the
raw data being sent by PA to the sound card, to try to know whether this issue
was in PA or somewhere else (e.g. kernel driver). After doing that, I copied
that dump file to my personal laptop and played through pacat and could
reproduce the noises too, so indeed it seems PA is sending broken data.

Note 2: Following the lead by the previous experiment, I've found that not
using mmap in the alsa sink (using unix_write() instead of mmap_write) will NOT
produce any noise when changing volume or switching output devices. I did this
by commenting the load-module lines for module-udev-detect in
/etc/pulse/default.pa, and then explicitly loading module-alsa-card with the
parameters shown by pactl list, but setting mmap=no.

Note 3: Following the instructions in
https://wiki.ubuntu.com/Audio/PositionReporting, I've already tried loading
module-udev-detect with tsched=0 and/or loading the snd-hda-intel module with
different values for position_fix, and none of those attempts work.


So, it seems to me that there's something wrong with the mmap path and this
device. Now attaching the output of alsa-info.sh, and will follow with a few
more attachments (and hopefully more comments) soon.

[1] http://www.gigabyte.com/products/product-page.aspx?pid=5038

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