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

cheater00 cheater00 cheater00 at gmail.com
Wed Dec 26 20:09:08 CET 2018


analog switch ICs are terrible, let's just skip them. You're not
making an analog switch ic based system anywhere near close a medium
sized modular, it's insanity and prone to shitloads of interference.
same with mod busses. the switch ICs are very proprietary. I haven't
found a digital multiplexer IC that was good, has anyone got any good
suggestions?

On Wed, Dec 26, 2018 at 5:16 PM Tom Wiltshire <tom at electricdruid.net> wrote:
>
> Why not make a number of “analog virtual patch cables” with analog switch ICs? Each cable has a switch at both ends, one selects between X sources, and the other selects between Y destinations. This is conceptually very similar to a genuine modular with hardware cables, but the control signals can be fanned out to however many voices you have.
>
> Alternatively, you could have a “mod buss” type system, where each module output could be sent to a particular destination buss, and each module input could be switch to tap signal from a given buss. Again, control signals for the switches in such a set-up can be fanned out to however many voices are required.
>
> For any polyphonic system (except the early oberheims?), the control panel is separated from the voice generation, so you can think about the interface separately from the audio-producing part of the circuit.
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
> > On 25 Dec 2018, at 22:40, cheater00 cheater00 <cheater00 at gmail.com> 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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