[PD] [GEM] advices about midi latency ?

pierre at 314r.net pierre at 314r.net
Mon Oct 7 11:38:31 CEST 2019

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


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