I am reposting some notes I made on some testing I did on MIDI timing with USB ports. These tests were all done on my desktop machine... 8years old or so. DMI: /IC7/IC7-G(Intel i875P-ICH5), BIOS 6.00 PG 04/27/2004 CPU0: Intel(R) Pentium(R) 4 CPU 2.40GHz stepping 09 2.5G ram. Sound IFs: - internal ac97, disabled in bios - PCI ensoniq used only for MIDI port. Turned off in pulse, not used in alsa or jack otherwise. - M-Audio D66 Used for everything - Roland Cakewalk USB MIDI IF used - advanced driver switch off (dumb mode?) This is my netbook midi IF used here for testing.
It had seemed to me that if I recorded a demo track from an external synth on the netbook, there were issues with timing that got better if /dev/hpt and /dev/rtc were added to the audio group. So I set out to measure this so I could "see" what difference various changes made. So far I am hitting my first problem. With this setup on this machine, there seem not to be problems as I had on the other machine. Maybe the track I started with is too easy, or qtractor sends more information for timing than my external synth. Any ideas? Below are my tests: >>> Created a track on hydrogen. Solid quarter notes, bas drum on 1 and 3 >>> snare on 2 and 4. >>> try 1) Stock 12.04 HPT setup. >>> hydrogen -> a2j -> ensoniq midi -> cable -> ensoniq midi -> a2j -> >>> qtractor (recording) >>> Examining notes in qtractor shows all notes are late by about .005 of a >>> bar (120bpm) +-.001 >>> - re-recorded on second instance of qtractor: >>> qtractor0 -> a2j -> ensonic midi -> cable -> ensonic midi -> a2j -> >>> qtractor1 >>> notes on second record (testing play and record) are ahead (bar time >>> delayed I guess) .015 +- .003 >>> Comment: not bad enough to hear >>> >>> try 2) I thought about this and realized Jack and a2j may have effected >>> those results. Try alsa only. >>> - take one >>> hydrogen -> alsa -> ensoniq midi -> cable -> ensoniq midi -> alsa -> >>> qtractor. >>> greatest error was .001, but mostly .000 ... That is no delay, but >>> same >>> variablilty. >>> - take two re-record on qtractor1 >>> qtractor0 -> midi cable -> qtractor1 >>> hmm same lead or more. Rerecorded midi is .018-.019 ahead. This must be >>> qtractor playback. >>> >>> Comment: The ensoniq seems to be quite solid. A2J adds some delay and >>> jitter, but not a lot. >>> >>> Try 3) Time to try a USB MIDI IF. Just for the record, the USB MIDI IF >>> has >>> male ends so I can't use a cable to tie them together, It will have to >>> be >>> a midi through. This may add some delay, but should not add jitter. >> >> - take one >> hydrogen -> usbmidi-> through -> usbmidi -> qtractor >> delay of .001 +-.001 >> - take two >> qtractor0 -> usbmidi -> through -> usbmidi -> qtractor1 >> delay of .014 Pretty consistent. +- .001 > > Comments: There is a difference from one port to the next, but it seems to > be transport. The notes don't seem to have jitter. They are all the same > amount ahead or behind. It does seem to be qtractor related. The stuff > coming out of hydrogen is very stable. > > > > -- > Len Ovens > www.OvenWerks.net > -- Len Ovens www.OvenWerks.net -- Ubuntu-Studio-devel mailing list [email protected] Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-studio-devel
