[pulseaudio-discuss] Variable resample rate

[Lennart Poettering]

On Wed, 22.04.09 19:14, s.jansen at gmail.com (s.jansen at gmail.com) wrote:

> My audio hardware supports multiple sample rates (44.1khz,
> 48khz,96khz) and I thought it would be nice if pulseaudio can
> automatically adjust the global resample rate based on the incoming
> stream(s). This to avoid any unneeded resampling if the hardware is
> capable of accepting the requested sample rate.  A simple scheme
> would be to set the sample rate to the maximum incoming samplerate
> of all streams. It would basically automatically scale up and down
> based on the max rate.

This has been requested before. I don't think it is feasable however.

Changing the sampling frequency requires reopening the audio
device. That will always result in discontinuities in audio. So, let's
say you take a phone call which is sampled at 8khz. Then an event
sound is played at 22khz. The device freq hence needs to be changed
from 8khz to 22khz for that short plop sound and then back again. Both
times you'd hear a short drop out. People would hate that.

Also, modern sound cards usually only do *one* sampling type and *one*
sampling frequency. Spending time on the logic you suggest is hence
probably better invested in speeding up the resampler or improving it
otherwise.

I'lll probably extend the current profile logic however, to allow
switching the output frequency with it. The most important reason for
that is digital output (spdif) since some amps cannot take 48khz or
cannot take 44khz and hence we need to allow the user to select which
freq he wants.

If that's in place it should be easy to add some code that switches
profiles based on a policy like you suggest. But I don't think this
would lead to much, but I am always happy to be proven wrong.

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
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