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If I modify /etc/pulse/default.pa and change this line:

load-module module-udev-detect

to:

load-module module-udev-detect tsched=0

I am clearly disabling tsched. Similarly if I change the line to,

load-module module-udev-detect tsched=yes

I am enabling tsched. Both of these are verifiable by running,

pactl list | grep tsched

And looking into documentation,

tsched Since 0.9.11. Use system-timer based model (aka glitch-free). Defaults to 1 (enabled). If your hardware does not return accurate timing information (e.g. Creative sound cards) you can try to set tsched=0 to enable the interupt based timing which was used in 0.9.10 and before.

However I have two machines (different hardware), one which returns tsched=yes and one which does not.

Is the default really 1 (enabled/yes)? Is there a way to verify that it really is enabled if it doesn't show up in pactl? What (in hardware) decides if it really is enabled?

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  • I confirmed this to work with Ubuntu 21.04
    – Troyhy
    Sep 29, 2021 at 5:19

1 Answer 1

10

There is a nice (technical) discussion here :

http://www.alsa-project.org/~tiwai/lk2k/lk2k.html

What's Sequencer?

The role of sequencer =
Delivers events at the right time (sequence) to the right destination (device).

So this has to do with how the kernel manages your hardware , in this case your sound card. Some sound cards (commonly Intel ones) need real time sqeuencing.

The Arch Wiki's page on PulseAudio/Troubleshooting says:

The newer implementation of the PulseAudio sound server uses timer-based audio scheduling instead of the traditional, interrupt-driven approach.

Timer-based scheduling may expose issues in some ALSA drivers. On the other hand, other drivers might be glitchy without it on, so check to see what works on your system.

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