Re: [LAU] MIDI jitter - Was: outfitting a computer for songwriting in linux?

On Mon, 27 Jul 2015 12:37:01 +0200, Clemens Ladisch wrote:
>http://lists.linuxaudio.org ... /2010-July/
                                 ^^^^^^^^^^^

I didn't read that tests again, but I guess we later made tests with
better results. Were the 2010 tests already made with jackd2
-Xalsarawmidi?

IIRC there were (later) tests made with jackd2 from svn and the
-Xalsarawmidi switch while HR TIMER - ALSA MIDI playback queue timer
res 1000000000 Hz was enabled. 2011 or later. My PCI cards and/or my
PCIe card had 0.0x ms jitter for the MIDI out to MIDI in loop
measurement. ^^^ Or perhaps even for the recorded MIDI instruments on
the audio tracks.

I don't remember if recordings to audio tracks were really that
synchrone too. IIRC there are several issues to consider. I guess the
0.0x ms were ok that time when recording to audio tracks, but IIRC there
always was around 1 ms for USB and it was audible.

Without jackd2 -Xalsarawmidi jitter increased rapidly.

jackd2's -Xalsarawmidi was new or fixed, I don't remember the year.

You always need to keep in mind that multi-track recordings could be
done one track after the other and the jitter of the MIDI events
recorded to the audio tracks has got positive and negative delay, so
1ms could become 2ms and 5ms could become 10ms.

An early reflection might be >= 5ms, but a similar effect already is
noticeable if the delay is shorter. If you record a synth or hihat
sample 2 times from a MIDI track to audio tracks to get a fixed phase
sound and there's just minimal jitter, everybody will hear the phasing
moving.

Better than measurements is simply making music. If there are no
audible issues, when recording MIDI to audio, then there are no issues.
If there are audible issues, then there are issues, what ever a
measurment would show.

In my experiences there are less often issues when using PCI/PCIe MIDI.
If it's wanted to use two external percussive sounds to become one
sound, then I wouldn't record them one after the other, as I did with
old sequencers, nowadays I try to record them at the same time or to
make a sound sample or ... I at least never ever would consider to use
USB MIDI.

Regards,
Ralf

PS: I won't to discuss this, resp. I have no time to continue this
discussion. Resume: If a musician doesn't notice an issue it's ok, if a
musician notice an issue, than it doesn't matter if most other people
are unable to notice it too. It's more likely that somebody is able to
notice jitter when using USB, than when using PCI/PCIe.
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Received on Mon Jul 27 16:15:03 2015