Subject: Re: [linux-audio-dev] midi events in jack callback (was: Reborn)
From: Paul Davis (pbd_AT_op.net)
Date: Fri Aug 16 2002 - 21:14:02 EEST
>We know that the ideal way of doing this is having both the sequencer
>and the softsynth access to the same exact clock for reference, then
>having the audio app a predefined "delay in time" consisting of the
>fragment size. After that it's a simple matter of taking the current
>time before mixing a block, and mix internally in smaller blocks
>while retrieving the event.
this is how you handle incoming MIDI data,yes. but outgoing data
is not a "simple matter" if you want to pre-queue the data and/or have
a resolution that matches the MIDI data rate.
> I see this as something JACK could do
>really well (take the timing before mixing a block and give it to the
>processes, so even if one has to wait for the other according to the
>graph, the sync with midi would be fine. I guess basically this alone
>may justify giving jack midi superpowers, since we know how important
>a good midi sync is.
yes, but "MIDI sync" isn't defined. as i've explained before, there
are two kinds:
MIDI clock: a low resolution "tick"
MIDI timecode: a low resolution positional reference
different kinds of devices use one or the other these, but rarely
both. most drum machines and analog-ish sequencers use MIDI
clock. most HDR systems and other digital audio systems use MTC.
syncing to these two things is a very different task depending on
which one you pick. MIDI clock tells you how fast you are moving, but
doesn't necessarily contain any positional information. Of course,
many systems may also generate MIDI song position data along with MIDI
clock, just to confuse matters :)
--p
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