Thoughts on Software Generated Envelopes

[Synthaholic]

On Thu, 18 Jul 1996 16:36:50 +0000 (), you wrote:

>DIYers:
>[...]
>As Juergen has pointed out in the past, the primary problem w/ SGE's is the
>main loop time of the processor.  Given the constraints of processing MIDI
>data w/ an inexpensive embedded CPU, your typical loop time is usually around
>1 msec.  If your CPU is feeding a DAC w/ 8bit values to generate the envelope 
>once per loop, this doesn't give you alot of resolution with a fast attack.  
>
>You could use a timer interrupt to tell the CPU to feed the DAC the next SGE
>value, but this usually has some overhead associated w/ it that will slow the
>CPU down considerably.

Perhaps this is not the way you can do it, but my plans are to use an
existing MC6800 (not 68000) with 24K ram several parallel interfaces
and a programmable interrupting timer.  I have a FatMan which has a
gate output.  I can connect the gate to an interrupt input on the 6800
to trigger it's 'programmed' envelope.  I can download and control it
thru a serial port.  I have a couple 1408L8s too... :)  Even though
this is a slow CPU, without the burden of MIDI data processing, I
should be able to get 10Khz data output rate.  Realistically, with
this CPU, probably only 2 or 3 channels.  I also have a 12 mhz 286.  I
could probably do this with a printer port and some latches and logic.
That could do alot more.  Hmmm, I have a PC-midi card too...



-- Scott Gravenhorst (Synthaholic)

"I didn't do it."
   -- Bart Simpson

www.concentric.net/~chordman