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

[Richie Burnett]

I'd definitely take a look at digital multiplexing options.

The "FM transmitter/receiver for every signal" approach sounds like an expensive and complicated way to add lots of noise, distortion and cross-channel interference to your signals on each modulation/demodulation cycle. Not to mention any potential FCC/Ofcom wranglings if you end up radiating significant RF energy from the metal enclosure or your RF-tight patch leads, and cause interference to a some nearby FM radio listener!

-Richie,

---- cheater00 cheater00 wrote ----

>I want to make this work for an all-analog synthesizer, but rather
>than use crosspoint switches I want to use patch cables which makes
>things much less annoyingly complex and expensive. The thing is, where
>on a monosynth you have a single patch cable, on a patchable polysynth
>you have n patch cables, one for each voice. So I am currently trying
>to work out how to do this using a single patch cable, and frequency
>domain multiplexing came to mind. I'm 100% certain an FPGA cannot do
>FDM, since almost all of this is analog, so I'm looking at dedicated
>radio transmitter chips. At $4 per chip, it's not so bad. The question
>is how to make the chips talk to a single medium without fighting each
>other.
>
>On Tue, Dec 25, 2018 at 11:24 PM Ben Bradley <ben.pi.bradley at gmail.com> wrote:
>>
>> What you're describing sounds all-digital.
>>
>> It seems to me a crosspoint switch would be the thing to have on each
>> (analog) voice, and have them controlled by the usual microcontroller
>> for a polyphonic analog-signal-path synthesizer. Of course, this is a
>> woefully incomplete description.
>>
>> On Tue, Dec 25, 2018 at 4:58 PM oren levy <orenlevysticky at gmail.com> wrote:
>> >
>> > You can use the FPGA to combine all the data you are trying to transmit into a single stream that you can transmit over a single cable.
>> > MADI interfaces are expensive as a unit. There are various ways to implement MADI at a board level with microcontrollers and FPGAs.
>> > Other options would be to make your own protocol. Using a TRRS cable should be able to provide enough bandwidth at more manageable speeds that won’t require you to think about transmission line theory.
>> >
>> >
>> > Rock & Roll,
>> > Oren Levy
>> >
>> > > On Dec 25, 2018, at 11:13, cheater00 cheater00 <cheater00 at gmail.com> wrote:
>> > >
>> > > The objective is to be able to create a way for a single patch cord to
>> > > carry 16 voices. I'm not sure how an FPGA in itself will help me, have
>> > > you got any ideas?
>> > >
>> > > MADI interfaces are prohibitively expensive.
>> > >
>> > >> On Tue, Dec 25, 2018 at 9:19 PM oren levy <orenlevysticky at gmail.com> wrote:
>> > >>
>> > >> I think you’d be better off using FPGAs so you can mux the signals however you want along with data. Either a bunch of small ones or one big one per module.
>> > >> If you just want to share audio and don’t want to mess around with FPGAs, you can probably use a protocol like MADI. Not sure if MADI has a DC coupling requirement but if not, CV could also be passed.
>> > >> You’d probably want a very stable clock to sync all the modules to and optimize clock phase delays so everything can mux/demux in sync.
>> > >>
>> > >> Rock & Roll,
>> > >> Oren Levy
>> > >>
>> > >>> On Dec 25, 2018, at 10:01, Mike Beauchamp <list at mikebeauchamp.com> wrote:
>> > >>>
>> > >>>
>> > >>>> 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.
>> > >>>
>> > >>> So there's $4000 worth of just one IC in a single complete polysynth?
>> > >>>
>> > >>>
>> > >>>
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