[PD-dev] jack dbus?

katja katjavetter at gmail.com
Wed May 29 19:12:21 CEST 2013

On Wed, May 29, 2013 at 5:00 PM, Jonathan Wilkes <jancsika at yahoo.com> wrote:

>>I checked it on Xubuntu: running Pulseaudio as an audio submixer
>>through JACK . In Pulseaudio's mixer GUI (which is the default mixer
>>in Xubuntu's panel), JACK can be selected as destination for an
>>application's audio output, but only when the application is indeed
>>delivering audio. For example, when a video is playing in Firefox, the
>>audio interface option boxes appear.
> So when you pause the video does the option box go away?

The controls for Firefox disappear when Firefox is closed, but also
when going to an URL without media stream.

It seems that the quickest way to make it work is: first make sure
that pulsaudio does not run (and is not autospawned), then start
jackdbus via QjackCtl, then start pulseaudio. This way, pulsaudio sink
and source are automatically connected in JACK, and JACK is
automatically selected as the sink for Firefox in Pulseaudio's mixer
(I don't get an option box any more).

>>Setting up the connections manually is time-consuming. But, since JACK
>>adds some latency to Pd, I would not use it as default (autostart)
>>setup. The lowest practical roundtrip latency through Pd I could get
>>in the JACK-with-Pulseaudio setup was measured 50 ms, 32 ms more than
>>directly through ALSA.
> Hm...
> http://jackaudio.org/no_extra_latency
> I'm talking about running PulseAudio on top of JACK and not the other
> way around.  Is that what you're doing?

I know only one way at the moment: routing Pulseaudio through JACK,
equivalent to how Pd is routed through JACK. If this is called
'Pulseaudio on top of JACK', then 'yes'. The extra latency is because
I need to set 2 periods of 512 samples (23 ms) for JACK's buffering to
get audio without dropouts in this setup. In Pd I have it fixed at 15
ms. In practice there are more causes for latency, so I measure
roundtrip latency in Pd with a sample-precise routine (see attached
patch 'latency-tester2.pd'). Pd's 15 nominal ms is in practice 18 ms
when routed directly via ALSA. Via the JACK + Pulseaudio setup it is a
total of 50 ms in practice.

By the way this does of course not say anything about latency in
Pulseaudio. Maybe there is a way to test that with a 'pulsified'
application, for example Audacity.

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