[pulseaudio-discuss] Pulseaudio sends out zeroes to sound card when no client

Lennart Poettering lennart at poettering.net
Mon Sep 3 06:42:29 PDT 2007

On Fri, 31.08.07 17:50, DSK (dsk.in.2007 at gmail.com) wrote:


>     I can see that module-detect after loading module-alsa-sink sends out
> zeroes to the sound card ( snd_pcm_writei )even when there is no client
> attached to the daemon yet ..
> Doesnt this consumes CPU cycles unnecessarily..
> Can't we do away with this ??
> I agree that this feature is available in autoloaded modles but then why
> does Pulseaudio has to write zeroes when its module(module-alsa-sink) is
> simply loaded using module-detect?

The primary reason for this is that most audio drivers produce
relative loud crackling noises when you open or close them. Upstream
ALSA is now working on minimizing these issues, but currently you get
those even with the newest intel-hda drivers.

OTOH keeping the devices open is indeed detrimental for power
consumption and hence PA from SVN (lennart branch, the upcoming 0.9.7)
now features a new module "module-suspend-on-idle" which will suspend
all devices when they are idle for too long. For the ALSA case this
means that the device is closed when idle.

So, if you want to save power and have sane sound drivers+hardware,
load that module. If you don't care about power consumption or care
about those crackling noises, don't load them. The default config will
now load it. 


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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