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MMC? (Or, external transport control with the Seq as timing master)


niklasni1
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I've hooked up an Akai MPD32 to my Seq V4 over USB. The Akai has transport controls that can either send MMC or MIDI messages (or both). The documentation is vague, but I'm assuming the MIDI messages are the normal real-time MIDI Beat Clock start/stop messages. The MPD32 actually also sends clock, since it has those 'note repeat' functions.

 

My Seq will slave fine to the Akai's clock, but I'd rather use the Seq as the master. (Also, the timing is *very* wobbly, but I'm actually not sure if that's a problem with the Akai or the Seq's USB MIDI?). If I set the Akai to not send clock, the Seq, as long as it is in slave or auto mode, will move from stopped to running, but since there are no clock messages it won't actually run.

 

If I set the Seq to master mode or disable clock input from the Akai's USB port, the Seq doesn't respond to the transport control. All in all, the transport controls on the Akai only work if it's the clock master.

 

So... is SeqV4 supposed to respond to MMC at all? If not, how would one go about adding it? It's basically SysEx commands. I'm looking at seq_midi_sysex.c but it's a bit hard to follow for me. Maybe in a few hours... I don't know if hardcoding it with the other remote mode commands is a good idea?

Edited by niklasni1
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It's still on the wishlist, but not implemented.

See also: 

(you are the only guy who requested this yet)

 

 

Also, the timing is *very* wobbly, but I'm actually not sure if that's a problem with the Akai or the Seq's USB MIDI?

 

Could you please check if this also happens if your Akai device is clocked from a PC via USB MIDI?

 

Best Regards, Thorsten.

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Ah, yeah, that thread. I've actually run the Seq as a slave to the old Fostex I'm talking about, and it works incredibly well. And I've also thought that it makes more sense for the device which requires audo frame-level accuracy to be the clock master.

 

I'd still really like the MMC commands, or the option to listen to real-time transport messages but not the actual clock.

 

The clock errors I'm seeing are on the Seq when it's synced to the Akai. You mean running MIDI clock from the computer through the Akai into the Seq? I can't test that right now as I don't have any MIDI DIN inputs on the Core...

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MIDI input working!

 

If I connect the Akai to the computer and internally loop the clock to the Akai's own DIN output and connect that to the DIN on the Seq, sync is much better. Over USB it'd swing maybe 10 bpm as displayed on the display, now it was wobbling 1/10th of a BPM as displayed.

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This doesn't really surprise me:

 

120.0 BPM = one MIDI clock tick each 20.83 mS

120.4 BPM = one MIDI clock tick each 20.76 mS

 

So, you notice a jitter of about 69 uS - is this really serious? ;-)

However, note that the displayed BPM is a mean value over multiple samples, and therefore dramatic peaks could be filtered out (there is no in-built statistical analysis over the clock quality...)

 

Do you notice an audible difference?

 

Some time ago I wrote a "clock accuracy tester" for MIOS32.

I haven't checked if it also works with USB MIDI host mode, but it's maybe worth a try: http://svnmios.midibox.org/listing.php?repname=svn.mios32&path=%2Ftrunk%2Fapps%2Fbenchmarks%2Fclock_accuracy_tester%2F

 

Here some typical measurement results (min/max/average delay): http://svnmios.midibox.org/filedetails.php?repname=svn.mios32&path=%2Ftrunk%2Fapps%2Fbenchmarks%2Fclock_accuracy_tester%2FREADME.txt

 

Best Regards, Thorsten.

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No, I think it's fine like this.

 

The other board is definitely broken -- can trigger timing glitches by sending lots of notes using the note repeat in the Akai, sometimes up to a 30 BPM drop. Good thing I had a good one to test!

 

I'd still like to make the transport buttons on the controller to work, somehow. Maybe just make normal start/stop messages work in MIDI clock master mode.

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