Ralf Mardorf wrote:
> Hi Fons :)
>
> fons@email-addr-hidden wrote:
>> On Sat, Mar 27, 2010 at 09:09:38AM +0100, Ralf Mardorf wrote:
>>
>>
>>> Regular it shifted between 2395 and 2404, but with a few exceptions,
>>> one time 2302, three times 2304, two times 2305 and two time 2494.
>>> See attachment.
>>> What might cause this exceptions? Could it be access to the RAM by
>>> the graphics? Is there something bad because of the IRQs?
>>>
>>> Regular shift 2404 - 2395 = 9 frames of jitter, exceptional maximal
>>> shift 2494 - 2302 = 192 frames of jitter.
>>>
>>> I guess this does mean ...
>>> 5.3 ms / 512 frames = 0.010351562 ms/frame
>>> Maximal difference for regular jitter 0.093164062 ms.
>>> Maximal difference for exceptional jitter 1.9875 ms.
>>> ... am I wrong?
>>>
>>
>> Wrong once or twice, if twice in such a way that the two
>> errors cancel out.
>>
>> First note that the test prints the difference between events. That
>> means that e.g. if *one* note is 100 samples
>> late you could see 2400 2500 2300 2400.
>>
>> The '2300' is just because the previous one was late,
>> not because this one arrives too early. So you should
>> divide the jitter as you measure it by two.
>>
>
> Aha, okay this is plausible.
>
>> Second, 5.33 ms = 256 frames at 48 kHz. But maybe you
>> are using 96 kHz ??
>>
>
> So you didn't read the attachment ;), yes I did use 96 KHz.
>
>>> If you play one drum sound after the other using hardware MIDI and
>>> you record one sound after the other to audio tracks, than jitter
>>> needs to be less 2 ms. I don't know how much under 2 ms, but more
>>> than 2 ms is audible and sounds horrible.
>>>
>>
>> I have some difficulty in believing this. It will sound
>> horrible of you mix sounds that have more or less the same
>> spectrum - any delay there will lead to cancellations.
>>
>
> No, let's say I would record the HiHat two times, than you would be
> right, this would be heard as a phasing and not as a bad timing, but
> if you would record first the kick and than the HiHat the groove would
> be broken, perhaps not for non-musicians, but for the gifted musicians
> I know and btw. for myself too, but because I'm the tester I prefer to
> refer to musicians who doesn't know that I playback the result of a test.
>
>> But doing that is a bad idea anyway, even without using
>> MIDI. You get the same problem if the same sound is captured
>> by two mics at a different distance.
>>
>
> Circulation period for stereo microphoning is a completely other
> issue. Just use a C64, Atari ST or any hardware sequencer from the
> 80ies. This jitter is unacceptable. Any musician having such a bad
> timing never ever would be allowed to study music on any German
> university. You need to differentiate. "Human touch" might be similar
> less precise, but please take a look at "less precise" syncopation,
> while the "human jitter" tends always to be to early, nothing bad for
> a syncope, for Linux MIDI jitter it also could be a little bit to
> late. Perhaps it's possible to cover a Lady Gaga song, but free jazz
> is impossible ... and it was
A typo
> impossible even for the C64 ;).
It was possible for the C64.
>> Second, 2ms is 0.6m, which is less than the size of a drum
>> kit. It is also less than the time required to send a 3-note
>> chord over MIDI.
>>
>> Finally, Jack MIDI uses ALSA when talking to HW ports.
>> If Jack can do it right, any application using ALSA should be capable
>> of doing that as well.
>>
>> Ciao,
>>
>
> If I understand your comment correctly you are saying, my system isn't
> bad, this is normal for Linux?
>
> If so, than Linux MIDI for hardware equipment can't be used by musicians!
>
> This is important for me. I could tray to get another PC for Linux, or
> I could try to repair my Atari ST.
>
> The timing issues are audible, not only for me, but also for musicians
> who don't know that some songs just were timing tests.
>
> Are you sure, that you are unable to here this by yourself? Please
> record a HiHat, a Snare and a Kick, one after the other. If you should
> have the same jitter, you might here the effect too. In addition play
> some syncopated chords to the drums. You should notice that the
> syncopation sometimes limps.
>
> :(
> Ralf
>
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Received on Sat Mar 27 20:15:03 2010
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