In my band, all musicians have both hands busy at any time. However, we want to add whole synthesizer chords (1/4 .. whole note length), maybe triggered by a simple foot switch every time (because playing along a sequencer is currently too difficult for us).
Some time ago I wrote a (Windows) console application in C (MinGW) that converted incoming MIDI events to text, piped that text to an external program (AWK script), and re-converted that external program's text output back to MIDI events. Basically every sort of filtering or event generation was possible; I actually produced chords triggered by simple control messages; I kept note-ONs in memory to be able to -OFF them whenever a new chord was sent, etc. - the actual processing (execution) times were not a problem at all(!)
But I had to understand that not only latency, but also the notoriously unreliable (with respect to "when", "for how long") user application OS multitasking/switching made this concept practically worthless at least for "real-time" use. There were always clearly perceivable delays, of unpredictable duration. I read about user-mode driver programming and downloaded some resources, but somehow stopped working on that project without a real result.
Apart from that specific project, I even have some experience in writing small "virtual" machines that allow for expressing exactly the variables, conditionals and math, stored as a token tree and processed quite fast. Maybe there is also the option to embed Lua, V8, or anything like that. So calling another (external) program is not necessarily the issue here, since that can be avoided.
The problem that remains is that the processing as a whole is still done by a (user) application. So I figure there is no way around a (user mode) driver, in this scenario.
Alternatively, I was even considering (more "real-time") hardware - a Raspi or the like - but then the MIDI interface may be an additional challenge.
Is there any hardware or software solution (or project) available that may serve as a base for such a _Generic MIDI filter/processor_? Apart from predictable timing behaviour, it is desirable not to need a (C) compilation environment when building filters/rules, since that "creative" step will probably happen in our rehearsal room (laptop available), which is certainly not a "programming lab". Text-based "programs" are fine - for long-term I'll maybe build a GUI for wiring/generating rules anyway.
