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

cheater00 cheater00 cheater00 at gmail.com
Tue Dec 25 23:40:24 CET 2018


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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