Scott Gravenhorst wrote:
I'm looking for advice regarding the design of a MIDI synthesizer.
...
Advice regarding this endeavor would be appreciated. Questions include which
of the
transfer methods will come closest to my goal of low latency (from time to MIDI
message
receipt to ..
Hi Scott,
Good to hear you're working with the new PI, it seems you've answered a lot of your own
questions already!
I haven't looked into everything about the time slicer, memory management (+ associated
kernel sources about page and segment management) and the connections of the various
hardware controls with the RPI cores and the various memory bus and other kinds of
contentions going on, I do recall from the Parallella forums that some one was using a
Linux boot command alteration to make the 2 core Zynq into essentially a 1-core Linux+
free core, if you want I could look that up for you.
My experiments with cors and Midi (like my long ago DSO based design
http://www.theover.org/Synth ) is very good in the sense of getting low latency going, so
I'd have some interest myself in connecting the graphics accelerated, 4-Usb port RPi
sensibly to (FPGA based) synthesis modules. It seems to me, given that any response speed
up to per-sample accurate (i.e. one audio sample delay between receipt of message and
starting a tone) could be your target, the following setup might be interesting to think
about (not necessarily to implement).
A (or more) midi message(s), or a message coming from a relatively simple piece of FPGA
that much quicker than MIDI scans a musical keyboard (I have some old keyboards lying
around that I wouldn't mind turbo charging) could be time stamped by FPGA, relatively (but
not super fast needed) send to for instance the RPI (or a Zynq based linux process, or
like in my case a classic version 1 RPI) , processed including the time stamp, send back
to the FPGA or send to a software module, and then WITH FIXED DELAY played into the chosen
audio stream. That way, latency can be small, but not near zero, which in a real time OS
is harder, but constant.
Theo V.
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