On Tue, Jun 4, 2013 at 3:08 AM, Jonathan Wilkes jancs...@yahoo.com wrote:
[...]
Sorry, I'm talking about a few things at once. One would be to test Pd by
itself
with ALSA backend vs. Pd by itself with JACK backend. That would provide
some data re: the page you linked to about latency. (My suggestion about
Pd-JACK + VLC-with-jack-backend-JACK was meant to cover that case
and also compare to Pd-JACK +Pulse-JACK, but as you say we can delve
into that later.)
The other is: what's a recommendable setup for using Pd in GNU/Linux
with acceptable/controllable latency while still behaving with the rest of
the
system. Your Pd/Pulse/JACK measurements help to address that.
You're right, JACK's latency 'discrepancy' should be investigated
separately. On my system I observe this behaviour:
- Pd with ALSA: measured latency is [Pd-nominal-latency + 3] milliseconds
- Pd through JACK with ALSA: measured latency is [JACK-nominal-latency
* 2 + 3] ms
- Pd + PulseAudio through JACK with ALSA: [JACK-nominal-latency * 2 + 3] ms
Here it seems that JACK's latency is double it's buffer size, no
matter if PulseAudio is connected or not. But wait, it's logical! The
loopback signal goes through JACK twice. Buffering is applied at
capture and at playback, and by default both buffers have size [frames
* periods]. Check with command jack_lsp -l. Optionally, extra input
and/or output latency can be added, however this does not reflect in
my measurements.
Apart from the effect that JACK's latency may be different from what
you'd expect, there is the effect that Pd + internet video requires
more buffering than Pd only. It's a pity that JACK's bufsize can not
be set in runtime.
It seems reasonable to expect and accept increased latency if you want
to play internet video's etc. together with Pd. Switching between
setups would be scriptable to make it easier (also see
http://gareus.org/wiki/qjackctl_dbus). But for the moment, I even get
stuck many times when switching 'by hand'. Apparently, the order of
operations is very critical. If it goes wrong, getting the d-bus error
from JACK I haven't found another option than kill the jackdbus
process and try again.
Katja
___
Pd-dev mailing list
Pd-dev@iem.at
http://lists.puredata.info/listinfo/pd-dev
