[LAU] JACK MIDI latency -- was Re: Concerning schedtool

[Ralf Mardorf]

IIUC we are not talking about the same alsarawmidi.

On Sat, 2014-04-19 at 18:18 +0200, Ralf Mardorf wrote:
> jackd --sync -Xalsarawmidi -dalsa -r$sample_rate -p$frames_period
 ^^^^^        ^^^^^^^^^^^^^
On Sat, 2014-04-19 at 19:47 +0200, Robin Gareus wrote:
> jackd -S -dalsa -dhw:2 -r48000 -p64 -n2 -Xraw
          ^^^^^^                         ^^^^^

Take a look at an older thread:

From: Devin Anderson
To: Paul Davis
Cc: Ralf Mardorf, linux-audio-user at lists.linuxaudio.org
Subject: Re: [LAU] midi backend not working in qjackctl?
Date: Wed, 14 Mar 2012 10:00:50 -0700

On Wed, Mar 14, 2012 at 9:04 AM, Paul Davis <paul at linuxaudiosystems.com>
wrote:
> On Wed, Mar 14, 2012 at 11:52 AM, Ralf Mardorf
> <ralf.mardorf at alice-dsl.net> wrote:
>
>> Especially in combination with Jack2's -Xalsarawmidi you'll get zero
>> hw MIDI jitter, aka hard real-time.
>
> I don't know if this is the new code that was added recently.
>
> If its the old stuff then it absolutely is not zero jitter. You're
> confused about the difference between "real time", "low latency" and
> "jitter". The whole problem of the old code is that was absolutely
> "deliver it as fast as possible" and that is precisely is what causes
> jitter.

The 'alsarawmidi' slave driver in JACK 2 does not have this problem.
It postpones the delivery of events based on the audio buffer size.
Back in April, when I requested MIDI latency/jitter test results for
the driver, I saw peak jitter results as low as 60 microseconds.

The 'seq' and 'raw' drivers attached to the ALSA audio driver still
suffer from this problem.

-- 
Devin Anderson
surfacepatterns (at) gmail (dot) com

blog - http://surfacepatterns.blogspot.com/
synthclone - http://synthclone.googlecode.com/