[sdiy] Patchable polyphonic synth with FM or AM transmission idea

[Richie Burnett]

Cheater, if I was doing this, I would be looking at 
Time-Division-Multiplexing rather than FDM.  (Yes you can pick up many 
different STEREO! FM radio stations on your radio, but these are generated 
by thousands of pounds worth of technology to achieve broadcast audio 
quality and ensure that they don't interfere with each other.  An "audio 
sender" FM transmitter chip is not going to get you anywhere near broadcast 
quality in terms of THD, noise, interference, etc.  And "FM broadcast 
quality" isn't actually THAT good by modern standards at all.)

*In my opinion* TDM would be much less hassle.

So if you want to send a sawtooth oscillator output for 8 voices down one 
patch cable I would time-division-multiplex them on to one cable, and then 
use sample-and-hold circuits at the receiving end to split the signals apart 
again.  Think how drum machines and early digital synths used to put more 
than one audio signal or control signal through a single decent-spec DAC 
because the cost of multiple DACs would have been prohibitive.

For synchronisation, you could have a global synchronisation pulse at the 
start of each frame, that every module gets fed from a backplane.  Or 
alternatively, you could embed synchronisation pulses into the TDM stream.

-Richie,