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

On 07/26/2015 12:17 PM, Ralf Mardorf wrote:
> Jeremy, we shouldn't discuss this in the original thread.
>

Hello Ralf,

Agreed.

> There are latency test measurements in the mailing list archive. PCI and
> PCIe cards show better results, IOW less MIDI jitter. There are also
> explanations why USB suffers from more jitter.
>
> The point of difference is, if the MIDI jitter is audible. It is! The
> measurements might not provide correct results. To measure a system by
> itself is a bad test and to measure a MIDI loop in addition is tricky.
>
> Jakob (living in Augsburg) from a Linux mailing list (perhaps LAU or
> LAD) years ago send me a board to loop through MIDI and that provides an
> audio output, to record the MIDI signal to an audio track. I never had
> time and interest to continued my MIDI jitter tests, so I still didn't
> use it. I guess this would be a better test, then the latency test.
>
> Howsoever, it's better to use PCI or PCIe, IIRC some USB interfaces
> even fail(ed) the latency test that measures a MIDI loop. The USB
> interface I own doesn't fail the test, but I'm anyway not satisfied and
> use PCI and PCIe MIDI only.
>
> That's it, I can't provide more information and I'm not willing to
> search the mailing lists archives.
>

Thanks, I'll dig through the archives to see if I can find related messages.

On 07/26/2015 11:42 AM, Ralf Mardorf wrote:> On Sun, 26 Jul 2015
11:01:46 +0200, Jeremy Jongepier wrote:
>> In the meanwhile the whole planet is using USB for MIDI.
>
> That's an assertion without substance.

I don't think it is. There are virtually no manufacturers that produce
great numbers of PCI(e) interfaces with MIDI and besides, the number of
new computers with PCI(e) is not that great too. That leaves basically
one choice, USB MIDI.

>
>> Please explain what is wrong with it, if possible with test results or
>> something else that confirms your assumption. I've never experienced
>> any jitter issues, not even with external MIDI gear.
>
> Search the LAU and LAD mailing list archives or edit a
> four-on-the-floor kick MIDI track. Play an external synth and make an
> audio recording of that kick, record the kick again and you'll notice
> that the kicks are never in sync, you'll hear an early reflection like
> shift or a moving phasing.

I'll give this a try, good suggestion, thanks.

 If you make syncopated or measure free music
> this is a serious issue, but it already is an issue if you want to
> sync four-on-the-floor kicks or similar. A lot of people claim that
> MIDI is not good enough to record "hand made" music, it always suffers
> from quantisation. To record really "hand made" music there's the need
> to do audio recordings. That's not completely wrong, but MIDI isn't that
> bad as many people nowadays think that it is. If you use a C64 or Atari
> ST and sync by klick or by SMPTE to a tape recorder, you get perfect
> sync.
> I noticed that shift of MIDI events is related to the used audio
> latency. The longer the latency is, the less precise is the timing of
> the recorded MIDI events on audio tracks. I never was able to get less
> audio latency than 5.3 ms (-r48000 -p256 -n2).

So that could be one of the sources of your issues. I mainly use -r48000
-p64 -n3 and honestly, I've never experienced any jitter issues. This
article seems to confirm that:
http://www.soundonsound.com/sos/Oct04/articles/qa1004-7.htm (one of the
first articles I could find on this issue)
Only the Larry Mullen Jr's of this world would notice jitter in that
case (http://www.newyorker.com/magazine/2011/04/25/the-possibilian). And
I'm no Larry Mullen Jr ;)

Jeremy

> FWIW there's zero audible (and perhaps zero measurable) jitter when
> using internal virtual synth. We don't know what exactly the OP want's
> to do, but she seemingly does use external gear.

> Regards,
> Ralf
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