What is the intended timing for MIDI messages sent by expression maps?

Dorico
1

I encountered a problem recently while programming Expression Maps for Synchron Percussion. I am using the sustain pedal (CC64,127) for the laissez vibrer technique in order to let the notes ring when indicated. When I use a tremolo to precede a note labelled “l.v.” (for laissez vibrer), the tremolo sample continues indefinitely instead of just hitting the l.v. note.

What is the timing for message techniques sent- this seems to trigger sustain pedal b4 the previous note ends
What is the timing for message techniques sent- this seems to trigger sustain pedal b4 the previous note ends1524×1020 72.4 KB

So I set up a test to check it out.

It turns out that a normal note and a tremolo note do not put out the same length. Here the note off message of the first note comes 3082 samples (approx 64ms @48Khz) before the sustain pedal message:

With normal whole note note off comes first by 3082 samples
With normal whole note note off comes first by 3082 samples1946×1274 86.8 KB

So that makes sense. The first note ends before the sustain pedal message is sent.

Now, with the tremolo note, the note off message of the first note comes 467 samples (approx 10ms) after the sustain pedal message:

With tremolo note the sustain pedal comes first by 467 samples
With tremolo note the sustain pedal comes first by 467 samples2324×1194 107 KB

This means that the MIDI messages sent by the expression map for the second note (the one marked “l.v.”) are being sent before the previous note ends, which is why the sustain pedal is catching the tremolo note.

How did the timings get crossed on this?
Is there an unintended legato being added to tremolo notes, extending them to overlap the next note?

2

So with more tests in an attempt to answer these questions,
it looks like the tremolo note is ending (sending a note off message) 10 samples (<1ms) before the next note (the one marked “l.v.”):

The note off of the tremolo is happening 10 samples before the next note
The note off of the tremolo is happening 10 samples before the next note1774×878 44.7 KB

but the CC64 sustain pedal message is being sent by the expression map 528 samples (11ms) before the note on that it belongs to!

Expression map is sending MIDI messages 528 samples before note on
Expression map is sending MIDI messages 528 samples before note on1468×678 32.3 KB

That’s a big problem!
There is no reason for the expression map to be sending MIDI messages that early! If you manage the gaps well, you can send 1 or 2 samples early to ensure that they arrive before the note on message, but 528 is unwieldy and totally unnecessary! MIDI messages do not take up enough bandwidth to justify sending them so early. In most use cases, MIDI messages sent at exact same sample will do, not needing to anticipate at all, as modern computers handle computation of basic MIDI very easily.