MicroDexed Teensy based DX-7

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paperCUT
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MicroDexed Teensy based DX-7

Post by paperCUT » Thu Sep 05, 2019 3:25 am

https://discourse.zynthian.org/t/microd ... to-go/1989

With the new teensy coming out this could be a really nice module, anyone investigated the project?

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mxmxmx
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Re: MicroDexed Teensy based DX-7

Post by mxmxmx » Thu Sep 05, 2019 4:10 am

paperCUT wrote:https://discourse.zynthian.org/t/microd ... to-go/1989

With the new teensy coming out this could be a really nice module, anyone investigated the project?
i did, briefly (see here). that was just using a suitable T3.6 + PCM1502a contraption that i had laying around; sounded promising (bit nicer than, say, preemFM 2, but maybe i was making that up). i basically just dropped in bits of the engine though, the tedious part ("UI") i didn't feel like doing. i sometimes use it as a user-unfriendly FM thingie...

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Post by DMR » Thu Sep 05, 2019 3:55 pm

Would the DX7 / Dexed really make a great module though? A polyphonic synth with a large number of parameters doesn't seem like it fits well with the modular paradigm, to me.

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Post by Kroaton » Fri Sep 06, 2019 4:08 am

Dexed's desktop VST interface is about as good as it gets for this sort of thing and it is free. I wouldn't bother running this on an embedded board just to have to somehow control 140+ non-intuitive cross-modulating parameters which affect the sound in mostly unexpected ways.

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Post by mxmxmx » Fri Sep 06, 2019 5:38 am

DMR wrote:Would the DX7 / Dexed really make a great module though? A polyphonic synth with a large number of parameters doesn't seem like it fits well with the modular paradigm, to me.
don't know. the greatness of the module, i suspect, would largely depend on 1) personal preference, and 2) the specifics of the implementation. the main potential attraction as far as can see is that one could conceivably CV the thing ("the modular paradigm"?) at decent sample rates, unlike, say, some OPL3-based module, or VST; whether that will result in a lot of sweet spots, or a nice UI, is probably a different question; but then eurorack shouldn't exist if that were somehow very serious criteria ... at the very least it'd probably afford (as they say) different kinds of usage, ie vis-à-vis running your favourite FM soft synth through an ES-8 or the like.

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Post by ranix » Fri Sep 06, 2019 6:54 pm

modular CV wouldn't help a DX-style synth, but a good interface with dedicated knobs for things like envelope parameters would. When you've got 6 envelopes with 8 parameters each (a,d,s,r with rate and level) setting up your envelopes is very frustrating. Even Dexed doesn't make it smooth imho, that's too much mouse clicking and takes way too long. The Jellinghaus and Dtronics programmers help but it sucks that the knobs don't adopt the correct position when you switch patches.

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Post by consumer » Sat Sep 07, 2019 12:47 am

I was just looking in on this forum specifically because I was thinking of a DX-style FM synthesizer... Imagining that one could develop an interface that chained operators... I had been playing with my PreenFM2's and imagining an interface that was more fun. (No slight intended to the wonderful PreenFM2).

First, let's assume that 1 single module can be 1 single operator. Should one want an eight operator synth, one must build eight modules.

I think in the modular realm, what we would want would be control to limit to range of modulation of each input. We typically do this by CV attenuators, and in this case let's imagine that we have dual operation; e.g. no input provides a 0 - 5v range (assuming that's the comfortable range of the chip), but with an input it's range is limited by the knob position. Sounds modular, right?

Theoretically with eight potentiometers and ten inputs this could be built into 8hp. 6hp is possible, but that would suck even more. But let's say 8HP per operator. That would be 64hp for an 8-op synth.

Doesn't sound bad to me, compared to other 8-op synths around... Those that I own that don't have CV input, nor immediate envelope controls.

I came here to re-read the FMOgre thread, so maybe I'm re-writing an already honed wheel.

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Post by ranix » Sat Sep 07, 2019 10:11 am

consumer wrote: First, let's assume that 1 single module can be 1 single operator. Should one want an eight operator synth, one must build eight modules.
If using a module like the Happy Nerding FM Aid, which takes an input sawtooth and produces an output waveform (sine, triangle, saw, square, your choice) which can be frequency modulated, you only need one FM Aid per operator you want to have modulated. So, you don't need to use an FM Aid operator to modulate another FM Aid operator if you just want to modulate it with a sine wave that's not itself being frequency modulated. You can just use a normal oscillator.

Often you'll want to modulate multiple operators with modulators of the same frequency, and in that case you can just use one oscillator to generate that frequency and mult it to several destinations.

The difficulty in complex FM in modular is dealing with frequency drift and the chaos that happens when your modulators don't have perfect (1:2, 3:2, 5:4 etc.) frequency relationships to the carrier. With just one modulator you have a lot of leeway but when you start stacking modulators in complex ways the desync causes chaos that sounds displeasing.

So I don't know how much value one would get from having CV control over the operators themselves. CV control over the envelopes would be awesome.

I don't know how I would handle polyphony in such a module, I think that would get confusing really fast.
consumer wrote: I came here to re-read the FMOgre thread, so maybe I'm re-writing an already honed wheel.
I don't think that's likely, there's a lot of unexplored territory here.

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Post by C0d3man » Tue Oct 29, 2019 4:16 am

Hi guys,

I am the one who ported Dexed to the Teensy. Currently we are working on the next step: Teensy-4.0 support, Support for OLED display, better menu, more FX (reverb, chorus), changing and loading sound parameters via SYSEX, storing sounds and parameters (like controller ranges and assigns) in separates configs, multi engine dual/split mode (like DX7II).

On the T_3.6 you get 16 voices when disabling the reverb (with reverb and filter only around 10 voices). With T_4.0 there is much more possible. Currently it works (single engine) with 16 voices and all FX at 50% CPU.

For T_3.6 there will be PCBs available soon (in fact kits are available but I am not ready with the assembly docs, so reading the circuit diagram is necessary).

T_4.0 currently lacks on USB-host support... so the next boards which will support T_4.0 and perhaps 8 free routable CV inputs will come at the end of 2020 or later. But you can build your own T_4.0-based MicroDexed because the source code is free on coderberg.org.

Regards, Holger

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