[PD] [GEM] advices about midi latency ?

Christof Ressi christof.ressi at gmx.at
Mon Oct 7 12:28:30 CEST 2019

> reduce pd audio buffer to 3

generally, you shouldn't run audio in the video process (unless you really need it). if you don't use audio (DSP is off), there is no need for latency and therefore the buffer size doesn't have any effect (in fact, a different scheduling mechanism is used where the message system is ticked every ~1ms). This means you should get MIDI input as fast as possible with low jitter. So turn DSP off in your video patch!

> all I want is to optimize midi latency

1 frame at 60 fps is 16 ms. MIDI latency shouldn't be your bottleneck. If you really want to minimize graphics output latency, then you would need to run at a higher framerate, assuming your hardware (monitor, projector) is capable. But what is your actual problem? Is it about your video output *noticeably* lagging behind your MIDI input?

> - tcltk could also be a problem because I have big patches

the Pd GUI runs in another process.


> Gesendet: Montag, 07. Oktober 2019 um 11:38 Uhr
> Von: pierre at 314r.net
> An: Pd-List <pd-list at lists.iem.at>
> Betreff: [PD] [GEM] advices about midi latency ?
> Hello all,
> somes questions here about midi process optimization :
> the midi setup :
> a korg electribe send midi message (noteon and controlchanges) to an
> usb soundcard (umc204hd) connect by USB to
> puredata/gem to finally draw things on screen (3d objects, videos
> textures, shaders etc) (nvidia hardware and drivers)
> all I want is to optimize midi latency and be able to draw things as
> fast as possible (considering this hardware)
> ie reduce the time between the midi event and the generated graphics
> what I've done :
> reduce pd audio buffer to 3
> use a 'delay line controler' to delay audio (something like 60ms is
> needed) and so retreive an 'good' A/V sync
> I know that :
> - double buffering add latency (and solve flickering)
> - somes videoprojectors add latency due to an internal video buffer
> - the more I can draw frames/second the more I can draw small events on
> screen (nyquist)
> - tcltk could also be a problem because I have big patches
> - when I measure midi lag by looping a midi message to and from the usb
> soundcard I get around 2ms, which is very good ! (tested with pd and
> also with alsa-midi-latency-test)
> any experience or advice on theses questions ?
> what are yours best setup/experiences to acheive really fast sync ?
> thanks you all
> Pierre
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