On 2016-08-13, Theo Verelst wrote:
For a class of applications where at least you would want sample accurate control messages, [...]
That's not about music-dsp, but dsp simple. There's a reason why all synthesis architectures out there make distinction between modulation and audio rate events. The first are supposed to be humanly understandable and deliverable even in real time environments. The latter are part of the inner workings of your synthesis algorithm.
[...] buffering for efficient pipeline and cache use dictates some form of delay control, which IMHO should be such that from Midi event to note coming out of the DAC, there is always a accurately fixed delay.
Not that many of us perfectionistas wouldn't have been thinking about this problem from the start...
So I though it might be a good idea to time stamp Midi messages with an Fpga (I use a Xilinx Zynq), and built in some form of timing scheduler in the FPGA to help the kernel.
That's plain overkill. All that you need is a well-synchronized realtime clock and a fast consensus algorithm. You can get the first over any extant Ethernet technology in controlled congestion state by using PTP ( https://en.wikipedia.org/wiki/Precision_Time_Protocol ). By rounding your events to the nearest microsecond or so, including time stamps, delaying your events a bit, and going with something like http://www.cse.buffalo.edu/~demirbas/publications/augmentedTime.pdf , you can approach perfection in latency and in fact attain it in local synchronization of the end result, quite without resorting to expensive hardware. Relatively cheap microcontrollers could keep up with that sort of thing any day of the week, without the total cost per node creeping past half that of a Pi.
I'm not talking about a hardware Linux "select()" call as kernel accellerator or single sample delay Fpga DSP, or upgrading to dozens of Fpga pins at a hundred times Midi clock rate doing clock edge-accurate timing, but an intersting beginning point for the next generation of accurate DSP software and interfaces.
"Accurate DSP software and interfaces." What you're talking about is form beyond function. If you want to do some super-sensitive remotely gated high energy shit in the CERN vein, go ahead. This is what you need. But that doesn't have much to do with MIDI signals or audio, anymore. Certainly not music.
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