[sdiy] programmable synth module

[john mahoney]

There's a module called the PSIM-1 that you can see at
http://www.synthmodules.com/.  A small number of PSIM-1s exist, but it's not
what you'd call "readily available," which is too bad because it's a really
cool module. As cool as it is, though, it did have room for improvement.
Let's look at the PSIM-1 for inspiration and try to invent a new version of
a programmable synth module.

The gist of the PSIM-1 is this: 4 analog inputs that feed an
analog-to-digital convertor; 4 analog outputs fed by a digital-to-analog
convertor; and, in between, a programmble microprocessor running the show.
It's possible to add MIDI inputs and outputs, too. There are Start, Stop,
and Reset buttons on the Frac Rac front panel, as well as 4 LEDs that show
the output level of each of the 4 analog outputs. There's also a fifth
output called Aux which can be used for certain things. I think the ADC and
DAC each have 10-bit resolution.

The PSIM-1 is programmable using a variant of the BASIC language; code is
written on a PC and loaded to the module. Programs load into Flash memory so
that you only need to hook up a PC when you want to load the module with new
code. A program was even developed that allowed you to load multiple
programs at once and select them using front panel buttons.

The PSIM-1 is capable of limited audio generation, but it's really too slow
for most audio generation and audio processing tasks. It's more of a
programmable control voltage processor and function generator.

The difference between a device that can handle audio and one that's limited
to CVs can be quite large -- this ain't no DSP! So, although it's tempting
to have audio capability, I would rather have a lower cost CV processor than
an expensive, programmable DSP module. And there is definitely a pent up
demand for something like the PSIM-1.


So, what can be improved over the PSIM-1? Here's a starting list:
-- more RAM
-- built-in MIDI in/out
-- more program memory
-- ADC and DAC optimized for handling pitch CVs (sufficient resolution,
etc.)

What's right about it?
-- direct-coupled analog ins and outs
-- versatile!
-- fairly easy to program
-- reasonable cost (they were $300)

What features would be nice?
-- ability for module to write data to flash memory
-- additional inputs and outputs
-- pluggable memory cards like Compact Flash or SD or something (the
cheapest ;-)
-- expandable RAM
-- faster processing is never a bad thing


Any suggestions for a core? Is the BasicATOM chip still the best way to go
for something like this?
--
john