[sdiy] Communications with voices in a polyphonic synth

[Carsten Toensmann]

Use a current loop hardware connection like MIDI uses. Current loop 
connections don't use voltages as 0 or 1 - transport but current differences 
and therefore are much less sensitive concerning influences of electric 
fields on long distance connections. I implemented a 1000 yards current loop 
data transfer connection between a UNIX host and a high rack warehouse where 
electrically driven automatic forklifts were driving around. So you had A 
LOT OF electrical influence.
This kind of connection is also used for data transfer processes in power 
stations. That is also one aspect why MIDI uses it in stage areas with all 
that cables, montor boxes and so on.
I use current loop connections for the module interconnection and 
communication of my new synthesizer project, see also

http://www.analog-monster.de/micronet_en.html

-Carsten

----- Original Message ----- 
From: "Tom Wiltshire" <tom at electricdruid.net>
To: "synth DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, March 10, 2010 8:15 PM
Subject: [sdiy] Communications with voices in a polyphonic synth


> Hi all,
>
> I'm currently tackling the above problem.
>
> I've already asked about SPI after encountering problems with it. It 
> seems to me that some of the problems that I'm having are because it 
> isn't really designed for single-master/multiple-slave communications 
> over distances of a couple of feet. I've used it to talk to DACs and  such 
> like, which is fine, because you've got a single master and  single slave 
> and they're more or less next to each other (distances  of a few 
> centimetres, not tens of centimetres).
>
> What I'm looking for is a way of talking to the voices. It needs to  be as 
> fast as possible (no-one likes latency), robust (there will be  other 
> electronic circuits in close proximity!) and as simple as  possible (but 
> not simpler).
>
> There are two aspects to this; the hardware level and the protocol.  I'm 
> currently not really sure where I'm at with either, and I'd like  to hear 
> people's views and experiences. Usually (I've found) there is  a wealth of 
> previous experience to learn from, both on this list and  by digging 
> through the circuit diagrams left to us by synth engineers  of old, who 
> have already faced these same challenges.
>
> Neil Johnson suggested RS485 to me as a possible hardware option.  This 
> seems like it would be good from the robustness point of view,  since it 
> is a differential signal, but I don't how it would do for  speed, and it 
> might require extra driver chips. I've looked at SPI  since it's what I 
> know best. I2C is the other one I've heard of. What  else is there 
> hardware wise?
>
> Protocol-wise, I need to be able to send parameter and control 
> information to single voices or groups of voices. How is this  typically 
> done? I can see easily enough how I can give each voice an  address, and 
> then send an address message ahead of a data message (or  group of 
> messages, I suppose), but how do I talk to a couple of  voices without 
> repeating the message for each?
>
> Sorry to be asking so many  questions, but this sort of stuff is  where 
> googling isn't so good, because (1) it's pretty specialised and  (2) I 
> don't really know what I'm asking.
>
> Any relevant experiences or pointers to useful material would be  greatly 
> appreciated.
>
> Thanks,
> Tom
>
>
>
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