Re: [LAD] ALSA MIDI latency test results are far away from reality

From: Ralf Mardorf <ralf.mardorf@email-addr-hidden-dsl.net>
Date: Wed Jul 14 2010 - 17:22:27 EEST

Hi Robin :)

On Wed, 2010-07-14 at 15:44 +0200, Robin Gareus wrote:
> On 07/14/2010 03:23 PM, Ralf Mardorf wrote:
> > [..]
> > AND IT'S AUDIBLE THAT THERE IS MUCH MORE JITTER BUT 1.1 ms.
> >
> > Any hints how to solve this are welcome.
>
> Did you try to start jackd with -p64 instead of -p1024

A good argument, because when I made tests in the past for the USB MIDI,
things become better at >= -p256 (when I had this Windows test install
latency for the EWX 24/96 audio was less high than for Linux). The
problem here is, that I need at least -p512 and even than I'm not safe
regarding to issues for JACK audio, that's why I used -p1024 instead of
-p512. For a test -p64 should work, but when recording music I would
need to increase it step by step until a minimum of -p512.

IIRC when I did tests for the USB MIDI with -p64 or even -p125 (I'm not
sure) it theoretically did work, but this isn't a solution, because at
some point JACK audio will fail.

> using JACK-midi, I've encountered a similar issue with fluidsynth always
> synchronizing note-start/ends to jack cycles.
>
> Simply lowering the frames-per-period got me playing again so I did not
> check if it's related to JACK-midi or FluidSynth 1.1.1 in general.

At least FluidSynth DSSI (host is Qtractor) is able to play in unison
with any DSSI or virtual ALSA MIDI and JACK MIDI (-Xseq) synth on my
machine. Just 'in unison' for virtual synth to hw synth there sometimes
is more delay, but just an early reflection like effect.

Note! It was hard to groove when I connected the master keyboard to ALSA
hw MIDI in --> DIRECTLY TO --> ALSA hw MIDI out and this to a 100% ok
drum module. Directly connecting the master keyboard to the drum module
there were no issues.

I need to do something else now, but I take time off. From Friday
(perhaps earlier) until next Sunday noon I could spend the whole days
for this MIDI issue only.

Resume:

I assume that -p64 would solve this 'looooooong early reflection like
effect/async', but then hard disk recording will become impossible.

The target is, that Linux at least replace the Atari ST as sequencer +
an analog 4-Track machine synced by SMPTE. With -p64 4-track recoding
would become impossible.

'Read you later' today or at the latest on Friday.

Cheers!

Ralf

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Received on Fri Jul 16 20:15:03 2010

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