Re: MIDI transport

On Thu, Aug 20, 2020 at 09:51:08AM +0200, Jeanette C. wrote:
> Hey hey,
> to what does midish react in a way of transport controls, i.e. relocation,
> starting from an offset?
> 
> On my system I use a program called jack_midi_clock paried with a metronome
> that provides the necessary tempo information. On the audio side a time
> offset can be set to start, which the metronome will follow.
> 
> The moment the start time is not 0, Midish will not follow a start command.
> When the starting time is set to 0, Midish is perfectly in sync with the
> external clock application. So I think the relocation is somehow passed on.
> Does Midish perhaps have constraints to what it can react?
> 
> It's a difficult situation, since I don't exactly know what jack_midi_clock
> outputs and what I should have to look for in the output in terms of
> messages.
> 

Hi,

Not an answer to your question, but here's at least how midish does
the synchronization & transport. It can synchronize to a DAW using
either MIDI Time Code (MTC) or to a MIDI sequencer using MIDI clock.

- MIDI Time Code. Basically, the clock master sends a message 100
  times per second, it's a kind of wall clock that counts fractions of
  seconds. The tempo and note lengths are derived from this clock
  source as it was the system clock. Tempo changes are handled by
  midish.

- The MIDI clock mode, uses Start / Stop / Song Position Pointer (SPP)
  messages for transport. To synchronize to the external sequencer, it
  uses clock ticks each representing 24-ths of a quarter note. This
  means that the tempo is provided by the external sequencer.

  IIRC, this mode is partially implemented, SPP is ignored.

My bet is that jack_midi_clock uses the "MIDI clock" mode, which would
explain why relocation doesn't work.