Ralf Mardorf wrote: > Hi Fons :) > > [email protected] 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 > _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
