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

Tom Wiltshire tom at electricdruid.net
Wed Dec 26 17:16:28 CET 2018


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?
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> Synth-diy mailing list
>>>>>> Synth-diy at synth-diy.org
>>>>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>>>> 
>>>>> _______________________________________________
>>>>> Synth-diy mailing list
>>>>> Synth-diy at synth-diy.org
>>>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>> 
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org
>>> http://synth-diy.org/mailman/listinfo/synth-diy
>> 
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy





More information about the Synth-diy mailing list