23 Mar
2011
23 Mar
'11
1:43 p.m.
1) it depends on the synth
2) with JACK MIDI, there is zero latency and zero jitter between two
applications. with ALSA MIDI, latency can be up to a few msecs, but is
generally on the order of tens of usecs. with ALSA, you don't have
deterministic scheduling of the apps (in general) and that is the main
source of the latency and jitter. in addition, the MIDI data arrives
(via ALSA) in the wrong thread, so there is some delay involved in
getting it injected into the synthesis (process()) thread without
locks. with JACK, the MIDI data arrives in the right thread, with
sample accurate timestamps.
On 3/23/11, andy baxter <andy(a)earthsong.free-online.co.uk> wrote:
Hi,
I am thinking about a possible design for the second version of the
position sensing drum pad I have been working on, and I have a
question about latency. I am working around the assumption that 10ms
latency is about the worst it can get before people start to notice it
in practice, so I am thinking of building the pad in a way where the
normal latency is about 1ms, but it degrades to between 10-15 ms in
the very worst case (many simultaneous strikes and pressure variations
across the pad). Allowing this level of degradation would make it
possible (I think) to use an arduino rather than a faster processor,
which would be nice.
So the question is, where does this 10ms figure come from, and is it a
reasonable working value? I have picked it up somewhere but I'm not
exactly sure where.
Another question on this topic - once a synth is triggered (e.g. in
supercollider which I'm using at the moment) is the latency from that
point just the jack latency, or is there an additional latency that
comes with the synth?
Also, could anyone give me a rough idea of what level of latency and
jitter to expect when using alsa midi ports to send data between two
applications?
I'm having another look at my first version of the pad, and I'm trying
to get the latency as low as possible before I present it at LAC in May.
andy
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