[PD] Pd as a plugin: concept shift with JACK freewheel

[Lorenzo Sutton]

Longish post inspired by the recent discussion about 'Pd as a VST plugin'.

TL:DR: better use a modular JACK (freewheel) approach compared to more 
'static' Pd as a plugin approach.

I think that on systems with JACK Audio [1] (Linux mostly, but available 
on other platforms, albeit maybe not so common nor supported), it would 
be great to have solid JACK Freewheel [2] support instead of trying to 
embed Pd as a plugin in rather cumbersome, diverse and (probably) 
unstable, ways.

Actually JACK freewheel *does* work with Pd on Linux (audio only) with 
the [jackclock] external by Nicolas Bouillot [3] also used to interact 
with jack transport, although currently a bit cumbersome if interacting 
with other applications. What's the big deal? Freewheel is 'faster than 
realtime', meaning that when activated audio will be generated as fast 
as the CPU can. The key use case is generating audio to a file at the 
same time avoiding things such as xruns or other problems due to 
real-time operation. If you've ever used Ardour  [4] and exported audio, 
it is using JACK freewheel (and in fact you see the playhead moving 
forward faster than realtime as it processes audio...).

Now imagine instead of having Pd as an LV2, VST or whatever plugin in 
Ardour, you have your patch(es) open in usual Pd, connect tracks or 
busses to Pd, reconnect [dac~] to Arour's master et voilà :) - when you 
need to export you just run with freewhel mode.

Indeed, I _was_ already able to connect through JACK an Ardour audio 
output to Pd with some simple audio processing, and then, after 
activating freewheel mode with [jackclock], 'record' the output to a 
.wav file through both jack_capture and [writesf~] internally (the 
former more interesting for this use case).

So, just to shift points of view, IMHO strong JACK (maybe including JACK 
midi) and JACK freewheel support is somewhat more desirable in Pd 
compared to support for the many plugin types and platforms. If one 
thinks about it this is more in line with Pd's modular and dataflow 
approach, also in the long run might be more resilient to plugin format 
changes, license changes (see VST problems), as well as updates in Pd 
itself.


Lorenzo.
PS. Disclosure: this is not my first post advocating a freewheel 
approach in the (Linux) audio ecosystem compared to monolithic do-it-all 
audio software, but just as a user :) [5].

[1] Jack Audio
[2] Jack Freewheel in the JACK API: 
http://jackaudio.org/api/group__ClientCallbacks.html#gae797e2cde20faecb9be510c8873fbdd6
See also this interesting section in Louigi Verona's 'Linux Audio 
workshop': 
https://louigiverona.com/?page=projects&s=writings&t=philosophy&a=philosophy_linuxaudio#2
[3] https://github.com/nicobou/pd-jackclock
[4] https://ardour.org/
[5] See e.g 
http://linux-audio.4202.n7.nabble.com/JACK-Freewheel-mode-thoughts-td102077.html 
and 
https://www.mail-archive.com/rosegarden-user@lists.sourceforge.net/msg02632.html