4 Sep
2018
4 Sep
'18
1:57 a.m.
On Mon, 3 Sep 2018, Jonathan E. Brickman wrote:
Indeed, MIDI's 31.25 kbps gives (because of its
8+2 bit protocol) a rough upper
cap of 1500+ datacommands (including notes and timing blips...) per second, notes
being one byte per command, one more for value. And even if we use the old (and
lately often obsolete) 50% rule, that's still 750+ items per second.
A note on or note off is three bytes, chanel/command, note and velocity.
Running status (first byte doesn't change from event to event) allows a
second note on in the same chanel to omit the first byte. This is why some
controllers send note off as a note on with velocity 0. Using note on and
note off means note, release, note is 9 bytes rather than 7 bytes for note
on on_with_0_velocity, on. Anyway, 1k is about the highest one can expect
on a per event basis. "Realtime" events are single byte and patch events
are two bytes. rpn and nrpn events are a minimum of 9 - 12 bytes for the
first one sent but may be a little as 3 for a next value.... though good
practice pretty much demands sending the whole 12 bytes every time.
Jack always converts incoming midi to full three byte events. I do not
know if it sends using running status to hardware devices.
All midi "mixing" requires converting to full events as well as queuing
bytes event at a time.
It would certainly be nice to blow all of those
numbers away by two or three
orders of magnitude! And it would be gorgeous to have MIDI data simply pervade an
IP stage network, or an IP instrument network, or one multi-instrument box
through localhost, or a stack-of-Raspberry-Pis network, or a creative combo. I
don't like the idea of using CAT5e generally on stage, because MIDI DINs are just
There are high use/cycle cat connectors and cables designed for this kind
of use. Take a look at almost anyone who sells network snakes or stage boxes.
Most of these cables are 100 foot cables :) but I am sure shorter cables
(or longer) can be had. Yes this would mean adding the matching connectors
on each of the boxes you wanted to connect.
In the last day or two I have been playing with the
Mido library's documentation
examples, and just now found much more apparently practical examples:
https://github.com/olemb/mido/tree/master/examples
including what looks like two actual JACK<-->RTP-MIDI bridges in the
'ports' and
'sockets' subsections. Will be studying. Seeking much input :-)
It would be interesting to know what the throughput and latency is with
that setup. I have never thought of python as being particularly great for
real time applications. However, something that works is a great start.
The road from python to c or c++ is not too bumpy depending on the
librarys used.
--
Len Ovens
www.ovenwerks.net