[PD] midi latency pd -> alsa / jackd

Rob Bothof rbothof at xs4all.nl
Wed Jul 18 18:40:51 CEST 2012

>> thanx, I thought jack midi was only used by soundcards with midi 
>> support, like
>> some firewire cards for example..?
> ... and several midi applications ... and you can bridge the two 
> different systems if you need to pass midi on to an app that does not 
> support jack-midi.
> I am not sure how reasonable it would be for your usb connection to 
> use jack-midi rather than alsa-midi (perhaps jack-midi is mainly for 
> midi between
> applications rather than with hardware?), but it would be worth 
> looking into as it would help with the timing issues you have, 
> especially as you say you are trying to use midi much faster than the 
> original protocol allowed for ... which is obviously much more 
> possible over usb than serial.
> Simon

thanx for your response Simon,
I've been tweeking with the usb endpoints on my device and have already 
gotten a faster and steadier performance with alsa-midi via jack.
but it is a balance of how many bytes you can send at the same time and 
at what speed, as usb midi also support a bulk mode..you can
send up to 64bytes of midi messages at a single call but without a speed 

but for my purpose right now it works best with 4bytes at 1ms 
interrupt...as usbmidi is 4bytes i can send 1 message at the time
if wanted to use 8 so i can always send the platter info and another 
midi-message at the same time but then i need to adjust the speed already
for it to work properly

though connecting Pd directly to /dev/midi1 has no problem with all 
this.....i believe jack alsa-midi does a tme sync for midi with the audio.
i'm going to see if i can write a simple jackd wrapper for oss /dev/midi 
from one of the jack simple midi examples, or perhaps someone already did..
it seems a bit useless as the oss usb device is probably an emulation of 
alsa who is really driving the device, but maybe it works


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