[linux-audio-dev] Synchronizing sound to MIDI events?

[Albert Graef]

Denis de Leeuw Duarte wrote:
> If you have an evenly spaced font, here's a graphical representation of 
> the problem:
> 
> |...e.....e|e....e....|...ee...e.|.....e.e.e|....e...e.| midi events
> |..........|...rrr....|.rr.......|......rrr.|....rrrr..| rendering
> |..........|..........|ssssssssss|ssssssssss|ssssssssss| sound

Hi, Denis,

a while ago you posted a question concerning rendering audio in response 
to midi events. I've been thinking about that problem, too (I'm using 
PortAudio instead of Jack, but the fundamental problem of rendering the 
audio with the goal of keeping latency low while avoiding jitter is the 
same). I don't know whether you got any replies through lad, but I was 
curious what solution you would eventually come up with, so I filed your 
mail for later consideration.

My background is that I'm developing a functional programming language 
with MIDI and audio interfaces (based on MidiShare and PortAudio). I've 
recently started thinking about adding some softsynth functionality to 
that, so I'm facing exactly the same problem. Probably this is folk 
knowledge for audio programmers, but it's difficult to find anything on 
the web about that. I must admit, though, that I haven't taken a look at 
sources of other softsynth projects like fluidsynth or one of the 
modular synths out there yet.

Well, that being said, I would imagine that you'll have to record the 
exact offset (from the beginning of the block) at which the midi events 
came in, and then start rendering at exactly the same offset one or two 
blocks later, to avoid jitter. (Translating the midi offsets in, say, 
milliseconds, to sample numbers is trivial, just multiply the time with 
the samplerate and truncate or round to an integer.) At least that's how 
I would go about this, but I haven't actually implemented it.

So what solution did you come up with, and does it work reasonably well? 
If you don't mind sharing. :)

Cheers,
Albert

-- 
Dr. Albert Gr"af
Email:  Dr.Graef at t-online.de, ag at muwiinfa.geschichte.uni-mainz.de
WWW:    http://www.musikwissenschaft.uni-mainz.de/~ag