[PD-dev] jack dbus?

katja katjavetter at gmail.com
Mon Jun 3 13:09:44 CEST 2013


On Mon, Jun 3, 2013 at 9:04 AM, IOhannes m zmoelnig <zmoelnig at iem.at> wrote:

> On 2013-06-02 08:51, Jonathan Wilkes wrote:
>> Of course these are just the latencies in the settings-- I haven't
>> done the actual measurements yet.
>
> it would be interesting to have actual measurements.
> everything else is wild speculation.


Right. I would propose the following measurement protocol:

(setup/usecase A: Pd only through ALSA)
1. In Pd using ALSA backend, run sine test signal in 'Media > Test
Audio and Midi...'
2. Set Pd's buffer to lowest possible value such that there are no I/O
error messages or audible dropouts during 'normal Pd use', that is,
while clicking (radio)buttons or switching between already loaded Pd
windows.
3. For this nominal latency setting, measure actual roundtrip latency
via line loopback or speaker / mic loopback, using patch
latency-tester2.pd which was attached to my May 29 post in this
thread.

(setup/usecase B: Pd and PulseAudio through JACK/ALSA)
4. Set up a routing with Pd and PulseAudio as JACK clients.
5. In Pd, run the sine test signal. Simultaneously, play this video in
a browser while routing it's sound through PulseAudio / JACK:
http://www.youtube.com/watch?v=_63Cc6vPFVI&feature=youtu.be
6. For this combination, get the lowest nominal latency in Jack such
that there are no  I/O errors in Pd, or audible dropouts in either
audio signal. JACK must be restarted for a new buffer setting to take
effect. This is the most time-consuming aspect of the measurement.
7. For this routing and settings, measure the actual roundtrip latency
through Pd.

8. Report nominal + measured latencies for setup A and B, together
with relevant hardware and system info.

My results for Panasonic CF-19 1 GHz Core2Duo, Xubuntu 12.04, built-in
soundcard, no preemptive kernel:
- setup/usecase A: 15 ms buffer in Pd, 18 ms measured roundtrip latency
- setup/usecase B: 15 ms buffer in Pd, 23.2 ms (2*512 samples) buffer
in JACK, 49.3 ms measured rountrip latency through Pd

I would suggest we do Pd+PulseAudio-through-JACK discussion on pd-list
if we continue this. The how-to and details of it are not a dev topic,
though the consideration of writing direct PulseAudio support for Pd
is.

Katja



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