[LAU] MOTU AVB series sample rate issue, JACK, and PulseAudio

[Be]

On 09/19/2017 01:44 PM, Len Ovens wrote:
> In my opinion, run jackd as your audio backend and use PA only as a 
> desktop front end bridged to jack.

Yeah, that seems to be the best course of action. I set QJackCtl to load 
on KDE startup and put this in Options > Execute script after Startup in 
QJackCtl's settings:

pactl load-module module-jack-sink channels=18; pactl load-module 
module-jack-source channels=18; pacmd set-default-sink jack_out

That tells PulseAudio to send audio to JACK by default. (On Fedora I had 
to install pulseaudio-module-jack for that). Configuring PulseAudio to 
not load its ALSA backend would be annoying because I sometimes use my 
onboard sound card on my laptop outside of home (not for music, 
generally for hearing speech in videos).

But this is still annoying because JACK won't start when I plug in the 
Ultralite AVB until I wait a few seconds. Plus I have to make sure the 
Ultralite AVB's sample rate is set to the same sample rate I have JACK 
configured for, and if not, change it with the controls on the Ultralite 
AVB.

  Pulse should be started with both the
> ALSA and udev modules unloaded (or they should be unloaded prior to 
> bridging to jack). I have in the past used the PA -jackdus-detect 
> module, but now have a script that loads the jacksink/source modules the 
> way I want. It is important that PA does not see any physical device 
> when using jackd as PAs audio IF. The reason for this is that if PA can 
> find any device it will use sync from it and that device will limit the 
> jack master device to the device PA is synced to and (at least in my 
> case) not allow jackd to freerun properly.
> 
> So Ardour export with PA bridged and PA can see the internal (HDA) audio 
> IF equals crash. But if PA has no ALSA module loaded, everything is fine 
> and reliable. If you wish to send PA's output to another IF besides the 
> jackd master, use ALSA_out or zita-j2a to make it another jack output 
> and run it through jackd. There can be as many PA to jackd bridges as 
> you need (want) so that the movie you are watching can go through one IF 
> and the skype call through another.
> 
> By running jackd as the PA backend, you present PA with a "sound card" 
> that has a SR it knows it can't change (48k or whatever) and will do 
> what it needs to for the input and output to match.
> 
> -- 
> Len Ovens
> www.ovenwerks.net
> 
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