[pulseaudio-tickets] [Bug 62604] New: Crackling with snd-hda-intel / VIA VT2020 in VLC, Google Voice

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=62604

          Priority: medium
            Bug ID: 62604
                CC: lennart at poettering.net
          Assignee: pulseaudio-bugs at lists.freedesktop.org
           Summary: Crackling with snd-hda-intel / VIA VT2020 in VLC,
                    Google Voice
        QA Contact: pulseaudio-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: chrono2200 at gmail.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: core
           Product: PulseAudio

Further described here:
https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/751265


My hardware:
$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: VT2020 Analog [VT2020 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 1: VT2020 Digital [VT2020 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 2: VT2020 HP [VT2020 HP]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: Generic [HD-Audio Generic], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

$ lspci -v | grep -A7 -i "audio"
00:14.2 Audio device: Advanced Micro Devices [AMD] nee ATI SBx00 Azalia (Intel
HDA) (rev 40)
    Subsystem: ASUSTeK Computer Inc. M4A89GTD PRO/USB3 Motherboard
    Flags: bus master, slow devsel, latency 64, IRQ 16
    Memory at fe4f8000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: <access denied>
    Kernel driver in use: snd_hda_intel

00:14.3 ISA bridge: Advanced Micro Devices [AMD] nee ATI SB7x0/SB8x0/SB9x0 LPC
host controller (rev 40)
--
06:00.1 Audio device: Advanced Micro Devices [AMD] nee ATI Cayman/Antilles HDMI
Audio [Radeon HD 6900 Series]
    Subsystem: XFX Pine Group Inc. Device aa80
    Flags: bus master, fast devsel, latency 0, IRQ 86
    Memory at fe9bc000 (64-bit, non-prefetchable) [size=16K]
    Capabilities: <access denied>
    Kernel driver in use: snd_hda_intel


#23 in the linked bug report fixed the crackling for me, but it was recommended
that a bug report be filed.
In /etc/pulse/default.pa : I added tsched=0 to the end of load-module
module-udev-detect


#61 gives a more technical description that may be of use:
It's all very confusing with many people experiencing similar symptoms. But the
original logs look like a simple case of PulseAudio selecting a far too short
latency:

I: protocol-native.c: Final latency 201.00 ms = 0.50 ms + 2*100.00 ms + 0.50 ms
D: alsa-sink.c: Cutting sleep time for the initial iterations by half.
D: alsa-sink.c: Latency set to 0.50ms

And indeed, VLC version 1.1.8 requested tlength=200ms and minreq=100ms. A
similar problem affects more recent VLC versions with tlength=40ms and
minreq=-1 (overriden by PA to 20ms). It seems that when tlength is exactly
twice minreq, PulseAudio settles on an insanely small latency. That causes
frequent underrun in hardware buffers, accounting for the distorsion.

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