[Jack-Devel] How to use jackd as a 'system-wide' server?

[Chris Caudle]

On Thu, May 17, 2018 2:03 am, Christophe Lohr wrote:
> Maybe I can tell jack to use 16kHz sampling rate, and let it convert
> when needed.

Jack does no sample rate conversion, all ports always run at the sample
rate specified when jackd was started, but the comments in the asterisk
module indicated that asterisk would convert rates if needed.  I did not
check to see if it was using one of the resampling libraries commonly used
on linux, but I would assume that audio quality and constant latency is
much less of an issue for telephony, so changing over to a more modern
resampler with higher quality e.g. zita-resampler would not really be
worth the effort.

> The use-case is about voice calls. Humans are rather tolerant about the
> latency of a phone call. isn't it?

I would say yes up to a point, but 1024 sample buffer is very far under
that point.  As long as you get no over or under runs with the PREEMPT
kernel you probably will not have a need to use a full RT patch.

>> What app do you have connected?
>
> The app is the speech-to-text Pocketsphinx (the code is slightly
> modified for my needs)
> Pocketsphinx uses pulseaudio as audio interface. So I need its jack
> source/sink plugin.

OK, that is a little convoluted with all the different matching interfaces
required, but is actually a good use case for jackd and the dummy backend.

--
Chris Caudle