audio glitches occasionally

[dbaker]

I've noticed since updating to 16.04 that every now and then, audio playback - from any source at all, whether it be on the web or hard disk - becomes garbled for a few seconds.
I've had extensive driver issues with this (dual-booted) machine, all relating to graphics so far, but it wouldn't surprise me if the audio problem was also a driver thing.
So just wondering, has anyone else experienced this issue?

[GreyGeek]

Perhaps you can tweek a sound driver. Here are mine:

[FONT=courier new][B]:~$ lsmod | grep snd[/B][/FONT]
snd_hda_codec_hdmi     53248  1
snd_hda_codec_realtek    86016  1
snd_hda_codec_generic    77824  1 snd_hda_codec_realtek
snd_hda_intel          40960  3
snd_hda_codec         135168  4 snd_hda_codec_realtek,snd_hda_codec_hdmi,snd_hda_codec_generic,snd_hda_intel
snd_hda_core           73728  5 snd_hda_codec_realtek,snd_hda_codec_hdmi,snd_hda_codec_generic,snd_hda_codec,snd_hda_intel
snd_hwdep              16384  1 snd_hda_codec
snd_pcm               106496  4 snd_hda_codec_hdmi,snd_hda_codec,snd_hda_intel,snd_hda_core
snd_seq_midi           16384  0
snd_seq_midi_event     16384  1 snd_seq_midi
snd_rawmidi            32768  1 snd_seq_midi
snd_seq                69632  2 snd_seq_midi_event,snd_seq_midi
snd_seq_device         16384  3 snd_seq,snd_rawmidi,snd_seq_midi
snd_timer              32768  2 snd_pcm,snd_seq
snd                    81920  17 snd_hda_codec_realtek,snd_hwdep,snd_timer,snd_hda_codec_hdmi,snd_pcm,snd_seq,snd_rawmidi,snd_hda_codec_generic,snd_hda_codec,snd_hda_intel,snd_seq_device
soundcore              16384  1 snd

It could be a timing issue with one of the snd drivers. Take snd_seq, for instance:

:~$ modinfo snd_seq
filename:       /lib/modules/4.4.0-41-generic/kernel/sound/core/seq/snd-seq.ko
alias:          devname:snd/seq
alias:          char-major-116-1
license:        GPL
description:    Advanced Linux Sound Architecture sequencer.
author:         Frank van de Pol <fvdpol@coil.demon.nl>, Jaroslav Kysela <perex@perex.cz>
srcversion:     B85F6C72B0E538F5FE58E08
depends:        snd,snd-seq-device,snd-timer
intree:         Y
vermagic:       4.4.0-41-generic SMP mod_unload modversions 
parm:           seq_client_load:The numbers of global (system) clients to load through kmod. (array of int)
parm:           seq_default_timer_class:The default timer class. (int)
parm:           seq_default_timer_sclass:The default timer slave class. (int)
parm:           seq_default_timer_card:The default timer card number. (int)
parm:           seq_default_timer_device:The default timer device number. (int)
parm:           seq_default_timer_subdevice:The default timer subdevice number. (int)
parm:           seq_default_timer_resolution:The default timer resolution in Hz. (int)

The "parm" are adjustable variables related to the particular driver. They can be changed manually, in the case of snd drivers with great difficulty, or by setting options in config files found in /etc/modprobe.d/.
As root you can create "snd_seq.conf" in that directory and then add, for example:
options seq_default_timer_resolution=100
options ....
etc...

Not all modules have parms but list your sound driver modules out and keep track of the names of those which have parms, and the exact name of the parms. After you've made any changes run
depmod -a
to have the changes registered. Then reboot to activate them. There may be a systemd way but I haven't read it yet.

[Snowhog]

My 16.04, running in a VM, also experienced this garbled sound at the beginning of my Startup, and I think, Shutdown selected .ogg sound files. The Audio and Video Backend (System Settings > Multimedia > Audio and Video > Backend) installed here is Phonon GStreamer. This same behavior happens in 16.10 and KDE neon, also in VMs. 16.10's backend is also Phonon GStreamer, but KDE neon uses Phonon VLC as the backend. Maui 1 Aurora, in a VM, doesn't experience this garbling; at all. Interestingly (to me), it shows two backends -- Phonon GStreamer and Phonon VLC.

So I decided to add phonon-backend-vlc to my 16.04. I chose to install it without recommends (sudo apt-get install --no-install-recommends phonon-backend-vlc) to see if switching to that backend would make any difference. What I found, even after a reboot, is that the Phonon GStreamer backend was still present and in use, and the Phonon VLC backend was not listed, and apparently (?), not in use. However, my garbled sound in the startup file was gone. It played perfectly.

I'm not sure what to make of this, expect that maybe the packages brought in by the installation of phonon-backend-vlc 'fixed' the underlying cause. So, you might try installing phonon-backend-vlc using the --no-install-recommends option and see.

08 Oct 2016:

Well, garbled logout sound (first second or so) is back, so I guess the cause remains a mystery.

[dbaker]

Thanks to both of you.
I tried the vlc backend trick first, and unlike snowhog's machine mine actually listed it as in use in the audio settings, but it made no difference to the glitching.
Then I tried the module settings greygeek described. There are a lot of things one could tweak there and zero documentation of them, so I only tried setting the snd_seq resolution as in the example. That didn't make any difference.
I have another module there which isn't in your readout, which is called snd_hrtimer - it doesn't have any parms though.

If only I could find an explanation of what all the parms for the drivers do!

[GreyGeek]

... If only I could find an explanation of what all the parms for the drivers do!

That's at least TWO of us! But, I like experimenting around, if I can't find documentation on the mod ....

[Snowhog]

That's at least TWO of us! But, I like experimenting around, if I can't find documentation on the mod ....

"October 6, 2016, Earth Standardized Time. The localized space-time rupture that resulted in the destruction of the SOL system was verified to have been the direct result of unexpected consequences caused by this 'experimentation' by 'GreyGeek' (alias assumed; no other name found in existing archive records)."

Encyclopedia Galactica, Edition of 2312, Alpha Centauri Central Archives

[GreyGeek]

That's the funniest msg I have read in a LONG time!

[dbaker]

I have an update: due to a number of other issues, and a good experience with a fresh install of the development version of KDE Neon on my other machine, I decided to wipe my disk, repartition and install the non-development KDE Neon in place of Kubuntu. This has magically fixed all the strange issues I was experiencing, including the audio glitching. We may never know what caused it.

[dbaker]

...I may have spoken too soon in my last post. The glitches are still there, they're just less noticeable/have a slightly different quality. If anything, they remind me of the stuttering you might get when trying to play back audio while CPU usage is very high (this is a thing I'm sure I've experienced, but I can't think of an example right now).

[GreyGeek]

I found this possible cure browsing the web:

Once it stutters I always got rid of this problem by killing/restarting pulseaudio.

1. sudo killall pulseaudio
2. sudo pulseaudio --system=1 --daemonize

Or, this one.

[dbaker]

I don't want to speak too soon again, but I THINK THE SECOND FIX WORKED FOR ME! thanks