[sdiy] Digital Synth Module ideas ...

[Seb Francis]

As I was glancing though the page of possible future MOTM modules I was 
rather inspired by the MOTM-520 Cloud Generator VCO.  Whenever I want to 
get those big fat multiple detuned saw wave sounds I'm always forced 
into software since I just don't have a powerful enough analog setup.  
And while software gets close to the sound I'm aiming for, digital 
synths tend to sounds quite sterile .. to say nothing of the fact that 
creating sounds with a mouse just doesn't do it for me!

So since I have a spare 4xD PCB lying around I got thinking about what 
kind of a module I could build with it.  The PCB is rather large, and 
has 2 independent sets of stereo I/O CODEC and dsPIC processor, so I 
figured I may as well make 2 modules sharing the same PCB...

(1) DCO - hybrid digital & analog controlled multi-oscillator.
(2) FXP - audio effects processor of some sort.

My ideas are pretty well formed for the DCO part, but I haven't really 
settled on what to do with the FXP part.  On my to do list of 
modules-to-design-and-build-for-my-modular I have a crossfading VCA and 
a wavefolder.  Both of these could be easily achieved with this, but 
also many other things.  So I'm eager to hear suggestions :)

As far as I can see all these ideas will be compatible with the 4xD 
hardware, so those people who have a 4xD kit will also be able to 
download the 'DSM1' (as it will be called) software into their 4xD.

Here are my specification notes so far ...

DCO
===

I/O:
----
2x Audio In Attenuators
2x Audio In  (used for AF modulation, with clip LEDs)
2x Audio Out
2x CV In Attenuators
2x CV In     (used for LF modulation)
MIDI In/Thru (for pitch and parameter control - responds to note on/off, 
pitch bend, pitch bend range CC, various other CCs)
1x Gate Out  (for running external envelopes, etc.)

Oscillators:
------------
Multi-oscillator (e.g. up to 8)
Wavetable waveforms: Saw, Square, Triangle, Sine + samples of waveforms 
from various analog synths
Each of the 2 audio outputs can use a different waveform

Modulation inputs:
------------------
Pitch control by MIDI
FM CV - frequency modulation (audio frequency)
Spare CV - spare audio frequency input ... ????
Spread CV - frequency spread of oscillators
Phase CV - phase spread of oscillators

Controls (both panel controls and by MIDI):
-------------------------------------------
2x Waveform select - sets waveform for each output
Instability control - sets frequency spread instability
Number of oscillators control - sets number of oscillators
LED display?


FXP
===

I/O:
----
2x Audio In Attenuators
2x Audio In (with clip LEDs)
2x Audio Out
2x CV In

Possible functionality:
-----------------------
Crossfading VCA, Wavefolder, Other forms of wave mutation, Phaser, 
Chorus, ... ????