[LAU] MotU Ultralite AVB observations.

Fernando Lopez-Lezcano nando at ccrma.stanford.edu
Tue Mar 10 01:27:42 CET 2020

On 3/9/20 1:16 PM, Chris Caudle wrote:
> On Mon, March 9, 2020 2:56 pm, Fernando Lopez-Lezcano wrote:
>> This is further complicated by the fact that some software (ie:
>> pulseaudio) will change the sampling rate without you doing it manually.
>> For example, if you manage to start jackd at 48Khz and then stop it,
>> pulseaudio (if installed and enabled) will take control of the audio
>> interface and change the sampling rate to its default rate (44.1k).
> You can change the default sampling rate which PulseAudio uses with a
> configuration file option.

Yes, of course, except that is not a generic solution. The behavior will 
change depending on which sampling rate was last used by pulseaudio 
(depends on the last thing played back) - and which one you need to use 
in jackd. If those can be controlled then yes, it is a workaround.

A more generic solution would involve modifying jack so that it is aware 
that the sampling rate is not stable and it has to wait. But that is a 
special case - I doubt that would be realistic.

I guess the real solution would involve changes in the ALSA layer so 
that this behavior is hidden somehow...

(other ALSA clients, for example audacity, do start "playing" regardless 
of the state of the clock - it is just that there is no actual sound 
until the clock locks)

-- Fernando

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