Re: [LAD] JACK and ALSA elucidations

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To: Gianfranco Ceccolini <gianfranco@...>
Cc: linux-audio-dev@lists.linuxaudio.org <linux-audio-dev@...>
Date: Wednesday, March 12, 2014 - 12:12 pm

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On Tue, Mar 11, 2014 at 11:21 PM, Gianfranco Ceccolini <
gianfranco@portalmod.com.br> wrote:

>

As Jeremy noted ... JACK asks to use "N periods, or the nearest number of
periods it can". You apparently have a device that can only do 16 periods,
so when JACK asks for 2, it gets 16.

> if I call jack using -p128 / -n2 and the opening message states that ALSA

no, not at all. the total buffer size is always ACTUAL periods * period
size. So as Jeremy said, it will buffer 2048 samples. During each traversal
of that buffer, ALSA will wake the client 16 times, every 128 frames.

>

I have no idea why you think that. As I tried to explain, the period size
(256) is the interval between when ALSA wakes the client.

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On Tue, Mar 11, 2014 at 11:21 PM, Gianfranco Ceccolini <=
gianfranco@portalmod.com.br
> wrote:

And where does the 16 (from ALSA: use 16 periods for cap=
ture) affects?As Jeremy noted =
... JACK asks to use "N periods, or the nearest number of periods it c=
an". You apparently have a device that can only do 16 periods, so when=
JACK asks for 2, it gets 16.
if I call jack using -p128 / -n2 =A0and the opening m=
essage states that ALSA uses 16 periods for capture the sound card will buf=
fer a total of 256 samples and ALSA will wake the client each 16 frames?
no, not at all. the total buffer siz=
e is always ACTUAL periods * period size. So as Jeremy said, it will buffer=
2048 samples. During each traversal of that buffer, ALSA will wake the cli=
ent 16 times, every 128 frames.
=A0If I used -p256 / -n2 instead ALSA would wa=
ke the client each 32 frames?
I have no idea why you think that. A=
s I tried to explain, the period size (256) is the interval between when AL=
SA wakes the client.

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Messages in current thread:
[LAD] JACK and ALSA elucidations, Gianfranco Ceccolini, (Fri Feb 28, 5:58 pm)
Re: [LAD] JACK and ALSA elucidations, Jeremy Jongepier, (Fri Feb 28, 8:01 pm)
Re: [LAD] JACK and ALSA elucidations, Gianfranco Ceccolini, (Mon Mar 10, 1:51 pm)
Re: [LAD] JACK and ALSA elucidations, Alex Gagnon, (Mon Mar 10, 2:34 pm)
Re: [LAD] JACK and ALSA elucidations, Paul Davis, (Mon Mar 10, 2:50 pm)
Re: [LAD] JACK and ALSA elucidations, Paul Davis, (Mon Mar 10, 2:26 pm)
Re: [LAD] JACK and ALSA elucidations, Gianfranco Ceccolini, (Wed Mar 12, 2:26 am)
Re: [LAD] JACK and ALSA elucidations, Paul Davis, (Wed Mar 12, 2:50 am)
Re: [LAD] JACK and ALSA elucidations, Gianfranco Ceccolini, (Wed Mar 12, 3:21 am)
Re: [LAD] JACK and ALSA elucidations, Paul Davis, (Wed Mar 12, 12:12 pm)
Re: [LAD] JACK and ALSA elucidations, Jeremy Jongepier, (Wed Mar 12, 11:37 am)
Re: [LAD] JACK and ALSA elucidations, Paul Davis, (Fri Feb 28, 6:12 pm)