If you are worried, I would try to use alsa sequencer queues, where you specify when you want the event to be sent and ALSA makes sure its as accurate as possible.

https://github.com/alsa-project/alsa-lib/blob/master/test/playmidi1.c

This example sets the queue to use tempo but its possible to use clock time events, relative or absolute.

Anyway, a back of the napkin calculation shows that the old MIDI protocol at 32650 kbit/sec needs around 245 022 us to send a byte. Missing a byte should not make a huge difference. So you can not really get more precise than that.. on old DIN5 MIDI. USB MIDI is faster but many times limited by the same speed for compatibility.

Regards,

David

On Tue, 21 Feb 2023 at 00:35, Jeanette C. <julien@mail.upb.de> wrote:

Hey hey,
I'm experimenting with c++ trying to program something nice for MIDI. I'm now
experimenting with clocks, using both the standard c++ chrono library and the
boost chrono library. My example program sets a desired delta between ticks of
250ms. I see that there is a difference, since Boost chrono can also use
pthread thread parameters foor realtime scheduling and priorities.

With the standard chrono and thread library my ticks are usually out by
anything between 150.000 to 290.000 nanoseconds. Using boost a tick is out
anything between 110.000 to 124.000 nanoseconds. Yes, much better. But,
assuming that I correct the drift, does it make a difference for MIDI
instruments?

I know one of my MIDI instruments with a clock sync'able delay can be rather
touchy with MIDI clocks, but are there good estimated guidelines experience
values how precise ticks should be?

Best wishes and thanks for any help,

Jeanette

--
* Website: http://juliencoder.de - for summer is a state of sound
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