Digital DIY synths and DSP stuff

[Fraser, Colin J]

> -----Original Message-----
> From: Roman Sowa [mailto:rsowa at WizjaTV.pl]
> Sent: 11 January 1999 10:26
> To: synth-diy at mailhost.bpa.nl
> Subject: ODP: Digital DIY synths and DSP stuff
> 
> 
> 10-bit DAC PIC-based envelope
> Yeah I think it would be enough, but with 10-bits you have to
> use double precision calculations. Maybe no problem for C
> but I use assembler only. (I have no C!)
> Then we get to the point when analog ADSR becomes better option.
> Personally I'd use digital envelopes only in all-digital synth

I wouldn't use a PIC to generate an ADSR envelope as this is easy enough
with an analogue circuit (no point using a sledgehammer to crack a nut).

I've been considering using a PIC as the basis for a more complicated
'transient sequencer'.
This would be an slew limiter with rate, target and slope (log-lin-exp)
controls, driven by a PIC via a DAC, with a window comparator to tell the
PIC when the target level is reached. 
It would need an interface to allow input of the parameters for generation
of complex n-stage envelopes, with options for gate control, repeating
cycles etc. The number of stages would only be limited by the memory
capacity of the PIC, but a serial eeprom on an I2C connection could provide
greater, non-volatile storage of parameters.
The interface would consist of rotary encoders for rate, target and slope,
with a numeric readout of the stage number, and the values for the current
stage.

Unfortunately, this idea is at the end of a long list of projects waiting
for the day when my girlfriend is rich enough for me to retire ;-)


Colin f