[LAU] Connect pipewire to running JACK server

[David Kastrup]

Yann Collette <ycollette.nospam at free.fr> writes:

> Le 28/01/2022 à 16:40, ycollette.nospam at free.fr a écrit :
>> Nice, thanks for the hint. I will do some tests next week.
>>
>> ----- Mail original -----
>> De: "David Kastrup" <dak at gnu.org>
>> À: "ycollette nospam" <ycollette.nospam at free.fr>
>> Cc: "Tim" <termtech at rogers.com>, linux-audio-user at lists.linuxaudio.org
>> Envoyé: Vendredi 28 Janvier 2022 16:37:52
>> Objet: Re: [LAU] Connect pipewire to running JACK server
>>
>> ycollette.nospam at free.fr writes:
>>
>>> Can somebody share pipewire configuration files for low latency audio with pw-jack ?
>>> I am still struggling but maybe this is due to the audio USB interface
>>> I've got: FocusRite 18i8.
>> It's maybe not overly relevant for your case but I've had significantly
>> different experiences with, say, the Mackie Onyx Satellite and the ALSA
>> drivers by picking period sizes of 128 (which does not work without
>> periodic dropouts not marked as Xruns) and even something as low as 24
>> samples: apparently at least at 48kHz or 96kHz it is crucial to have the
>> period size divisable by 3.  And if it is, very low latencies are
>> possible while if it isn't, you get garbage.
>>
> I just tested the "multiple of 3" rule and effectively, it worked.
>
> With a buffer size of 256, I've got garbage and with the buffer of
> size 128 it's fine.

192? 96?

> How did you find this rule ? Trial and errors ?

Yes and no.  Some Windows ASIO drivers refused to do anything but that
for some Behringer USB card and worked with stuff as ridiculously low as
24.  And if you try converting period sizes to millisecs, you need that
factor of 3.

The Opus Codec has as smallest standard size 120 samples @48kHz
(2.5msec) .  Stuff like that.  48kHz needs that factor of 3 to map
nicely to millisecs.

It doesn't make a superb amount of sense to me I'll readily admit.
Maybe the actual rule is "avoid powers of 2" for some drivers and/or
hardware, and 3x2^n is about as far from a power of 2 as you can get.

-- 
David Kastrup