latency of MusicDeviceMIDIEvent and sampler device on iOS
latency of MusicDeviceMIDIEvent and sampler device on iOS
- Subject: latency of MusicDeviceMIDIEvent and sampler device on iOS
- From: Hamish Moffatt <email@hidden>
- Date: Mon, 17 Mar 2014 19:01:11 +1100
- Organization: Rising Software Australia Pty Ltd
Hi,
I'm playing MIDI out through the AUSampler device. I've got a few
samplers, a mixer and a RemoteIO output in an AUGraph, and I'm sending
note on and note off (etc) events to it at the right time with
MusicDeviceMIDIEvent. Because we're using the same code on OSX as well
as Windows we're doing our own timing, MIDI sequencing etc rather than
using higher level audio frameworks to do it.
Now this works except I'm getting some variable latency from when I call
MusicDeviceMIDIEvent until I actually hear the sound. For example we're
just playing a metronome, with a regular note on event every 120ms, but
sometimes the actual audio is 30ms late. The next event is back on time
though.
I'm sure we're calling MusicDeviceMIDIEvent accurately, timing it using
mach_wait_until() and mach_absolute_time().
I don't hear any issues at all running the same code on the Mac.
So is there some other way I should be timing this? I'm guessing yes
given the sample number parameter on the MusicDeviceMIDIEvent call, but
I'm not sure. Or something else I should be doing to fix this?
Thanks
Hamish
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