Yay, I've joined the MiST crew!
I got two MiSTs via Lotharek yesterday and have been exploring the MIDI as well as failing to get a hard drive image working.
I did some tests to see if the MIDI behaviour was consistent and I noticed two things, but the second one may be such a specialised case that it won't be worth fixing, but I hope so.
1) The MIDI out lacks enough current that all MIDI equipped instruments have, the (i think) 5 volts that powers certain midi equipment, such as a midi merger or splitter. I don't know if this is a limitation by the fact that the power supply is a USB charger(low amps), or if this is an oversight in the circuit modelling.
2) Speed is slightly slower than a normal Atari.
I usually use two ST's (or Mega ST or STE, it never matters,I have each kind, some with 1mb RAM and others with 4) both running the same software and sync them by hitting "play" (the spacebar.) The Ataris will stay in sync for as long as I let them run. I did a test earlier this year where I let two Ataris run for 4 hours after a spacebar sync. They stayed in time/sync the whole time.
Today I tried a similar test with the MiSTs and Ataris. It didn't take long (about 30 seconds) to notice that the MiST runs a few microseconds slower than the Atari. The two MiSTs stay synced together just as two Ataris would, but when I throw a real Atari ST in the mix, I can hear the Atari's sounds coming in earlier on the beat ever so slowly.
I took the liberty of recording this behaviour in the most controlled environment that was possible, so hopefully some measurements could be made to get an idea of exactly how much slower the MiSTs are running (and maybe fixed

).
The file below (mp3, 19mb) is ~20minutes, the audio is a 4/4 ~92bpm pulse of a snare drum in the left channel coming from an Atari Mega ST(via a drum expander triggered by MIDI), and a kick drum from one MiST(midi to drum exp.) in the right channel. Occasionally I bring in the other MiST (who sounds a snare drum as well) to see if it was remaining in sync with the other MiST (and it did.) At the end of the audio file you can hear that the St's snare drum is now a half beat in front of the (MiST's) kick drum.
file ->
http://we.tl/UmQdP51Gdr
It's a minor disadvantage, but having them run identical speed to the Atari (if this is possible?) would enable me to swap ataris and mists around in my studio or on stage like they are the same machine. As it is now I need to keep them on different teams. We ARE talking about a half beat every 20 minutes here so its very small , but thats no good for a musician, or the music!
The next test I'll do regarding this will be to see if the MiST MIDI Clock is detected at a different speed than the ST within a modern PC's DAW. When I send MIDI clock from an ST, I always get erratic numbers: like if I'm running ~92bpm, a modern software package's clock detection will jitter around that, going down to 91 and up to 93. I don't know if this reflects bad modern software or unsteady clock in the Atari, but since the ST's stay in sync with each other it never concerns me.
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Cheers
novoline