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

Vladimir Pantelic vladoman at gmail.com
Fri Dec 28 23:24:46 CET 2018

let's not forget why these solutions were developed in the first place, it was 
because the actual transmission channel was an expensive and scarce resource, be 
it a long distance phone cable crossing the Atlantic or a satellite link, in 
each case the added cost for mux/demux at the ends was still way less than 
adding more separate "wires".

in the use case here, having to mux/demux at every patch point will add way more 
cost and overhead than just running N lines in parallel, copper is still 
relatively cheap for short lengths...

On 27/12/18 14:55, Roman Sowa wrote:
> Frequency domain multiplexing was used long time ago in telephony.
> How nice and easy solution this was can be simply put in two questions:
> - why nobody remembers that?
> - why it was abandonned so quickly?
> I mean you have ready to use multichannel digital standards and multichannel ADc 
> and DACs, why bother using an ancient idea that was so troublesome to manage 
> that even 0.3-3.4kHz bandwith audio was a challenge.
> And if you want full analog, I'd go with multipin connectors, there are lots to 
> choose from. OK expensive patch cable then, but still a tiny fraction of the 
> price of any 16-voice module.
> Polysynths are hardwired for a reason.
> Roman
> W dniu 2018-12-25 o 20:49, cheater00 cheater00 pisze:
>> Hi everyone,
>> I was thinking again about how you could do a modular polysynth well,
>> and it occurred to me that you might be able to use frequency domain
>> multiplexing (FDM) to put several signals over a single conductor
>> pair. A quick search found the Si4710 which is a bit pricey at ~$12 on
>> digikey but it's a tiny 3x3mm QFN device that performs complete FM
>> transmission. In a 16 voice system, at about 5 output functions per
>> module, and 12 modules, you can easily use up ~1000 of those, which
>> drops the price to $4. I was wondering what everyone thinks about this
>> sort of scheme.
>> Given that metal patch cables could function as antennas and cause
>> both cross talk and external signal pick up, one could also use
>> multimode glass fiber and transmit signals this way. The question is,
>> does anyone know whether support electronics could be found that are
>> integrated enough (small in footprint) and inexpensive? The idea would
>> be to build an electronics module that takes 16 analog audio channels
>> and outputs a signal that can be then converted to glass media
>> signalling.
>> Merry Christmas everyone!
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