[PD] JACK on macOS

[Roman Haefeli]

On Tue, 2021-12-14 at 14:45 +0100, Christof Ressi wrote:
> > 2. turn on "callbacks" in Pd's audio settings (it seems that this
> > is 
> > required on macOS) 
> Are you sure? In my understanding, the "callback scheduler" is
> generally 
> legacy and usually you would always use the "polling scheduler".
> (Both 
> the Jack backend and the portaudio backend support both modes.)

Here's my experience with my on own (recent) Pd build on macOS Catalina
and with JACK from jackaudio.org:

Pd works fine with JACK. It works with 'callbacks' unchecked (default)
and with 'callbacks' checked. However, for me using 'callbacks' is not
at all legacy and it would hurt our team project if it would be
removed. From what I measured, the latency added by Pd with 'callbacks'
unchecked is roughly the number specified in 'delay(ms)'. With
'callbacks' checked, Pd behaves like many other JACK clients and
doesn't add any latency on top of the buffersize induced latency of
JACK. So, if low latency is a concern, it seems using 'callbacks' is
the the way to go. OTOH, I managed to kill ardour and jack while being
connected to Pd with 'callbacks' checked while the CPU was almost maxed
out. I think it makes sense to have 'callbacks' unchecked by default
for higher resilience, but I find 'callbacks' a rather valuable option.

That said, I never really understood what 'callbacks' means. To me it
looks like "polling scheduler" means that Pd maintains its own separate
(from JACK) ringbuffer whose size is given by 'delay(ms)', while
'callbacks' means no additional ringbuffer. 

@IOhannes:  re your request of Pd-JACK-macOS experiences: Probably more
interesting are the results with the proposed Pd builds that are
candidates for distribution than with my self-compiled Pd. I'll try to
test those soon.

Roman

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