In this video I’m discussing my latest approach on a polysynth:
9 Likes
I might look at doing something like this myself
1 Like
The arp in the demo sounds incredible, wow
2 Likes
It’s connected to my Keystep37, it has this nice chord and strum feature.
1 Like
Really good,
On the MUXED control voltages where you have the capacitors, did you try it without? given that the Arduino is running at 16MHZ is it not fast enough for there to be no noticable effect on the controls?
2 Likes
New rule: From now on any polyphonic synth must also be polyhedral. Rectangular prisms don’t count. Bonus points for stellations of the icosahedron.
2 Likes
You need the caps, even with a T4.1 running at 600 mhz
1 Like
Good observation. Actually here I have the most problems to get DAC and demux into sync and not bleed into another voice. So the caps are really helping and buying me some time. Also update cycles might vary depending on what is currently going on. It seems MIDI is quite costly. Or it’s my poor programming. It’s still a long road ahead.
1 Like
A good demux is hard to make, I’ve agonised for days over differing setups. I started looking at interrupt driven demux which is what most polysynths do to get the timing more precise, like you say, other tasks can upset the timing. I even did away with the sample and hold completely and just used 8 channel DACs in 2 designs, this way way the best solution. 4 DACs will give 32 channels of CV and the rest I use 74HC595 shiftregisters for on/off switches. But it’s also quite expensive, if I didn’t already have stock of 10 DAC8568 chips in stock I probably wouldn’t have done it.
1 Like
One thing I noticed, you built a demux, but no mux input to read voltages from controls and switches, how are you controlling it? MIDI CC messages only?
1 Like
The sample and hold stuff has been very good timing, I had not considered there to be an issue and had started designing my demuxed DAC a few weeks back…
For my design ( presently ) the programmer MCU will only read and write the control voltages and be dedicated to that function, so less work to do and less timing issues.
In my design it has the read muxes are on the same address bus as the write, so it will read a value from a control and either write it straight back out again or ignore it depending on the mode ( Live/Program)
Cheers 
Rob
1 Like
Currently I only have MIDI CC messages. My plan is to build a control board with display and rotary encoders that is connected via i2c.
I currently keep the two seperate input and output, but I’m considering putting them both onto the same loop.