Thank you Murray for explaining the complex workings of the JX-3P (and other DCO synths) so clearly and precisely!  

Out of interest, how do synths such as the Jupiter 8, Prophet 5 and Oberheim OBXa store their patches considering they are VCO rather than a DCO synths? I vaguely recall that the Jupiter 8, or the earlier models at least, were described as "12 Bit" so I assume that despite the VCO sound generation they are still using some form of digital circuitry for patch storage and tuning?  

On 2 May 2018 at 03:32, Murray Hodge yahoo@... [kiwitechnics] < kiwitechnics@yahoogroups.com > wrote:

 

Almost all synths that have the ability to save a patch use a MUX to control all the voltage controlled items in them and this part of the hardware is completely digital. These controls include filter cutoff, Resonance amount, VCA Levels etc etc. The big difference between 'digital' & 'analogue' synths is the way the note frequency is generated. The JX-3P for example uses digital dividers which output a square wave and the frequency (divide number) is written into them each time the note changes. This then needs to be converted into a Saw wave using hardware. The SH-101 for example uses an 'analogue' oscillator chip (CEM3340) and the frequency is still controlled via the MUX and the wave forms are done within the 3340 chip.

Unless the synth has a hardware ENV generator (for example the Korg PolySix, Korg Poly61 use a SSM2056 ENV chip) all envs are generated in software and output via the MUX to the various output parts that need control. Calculating the various control outputs is a very complex part of the code as there are many sources that need to be mixed together to make the final output for each control. For example the VCF cutoff may have LFO (various sources normal or plus), ENV level (various sources normal or inverted), Keyboard note (including bender & portamento) and note level, matrix output, control knob level and so on. Do this for each voice and each control and you can begin to see that the cpu is pretty busy. The JX-3P has 29 MUX control outputs and each of these has to be recalculated in real time and this takes up a lot of the processing time. When it is not doing this the cpu also has to scan the keyboard, scan the switches, scan the bender, send and receive midi and display all the leds.

In short the signal path from the DCO output to the synth output is analogue but everything else and all the controls are digital. Also if the DAC has a fault all the MUX outputs will also be faulty. If any of the 29 outputs are working then the DAC is working.

MH

On 2/05/2018 2:28 PM, Chas D 350ypvs@... [kiwitechnics] wrote:

 

Florian,

We appear to be getting terminology confused with each other.

The JX-3P uses digital CONTROL, but its actual sound generation is analogue (oscillators, amplifier, filter, chorus). I believe the envelopes are software generated. Many people incorrectly state that the 3P is a digital synthesizer, when it's actually analogue with digital control circuits.

A Yamaha DX7, Casio CZ and Roland D50 are fully digital, and use "digital oscillators", entirely different to "digitally CONTROLLED oscillators" as per the 3P. Many times I see the 3P incorrectly described as having digital oscillators or being described as a digital synth. A digital oscillator requires a digital to analogue converter to convert digital data to analogue audio, much the same way that a CD player uses D/A converters to convert digital information on the disc to analogue audio where it can be heard with the human ear.

This is what I took the OP's post to imply when he talked about D/A converters being faulty, because if it were a fully digital synth, then that would explain the loss of all audio. With the 3P, that wouldn't apply because of the 3P's analogue signal path. If the OP was talking about the 3P's digital control circuits with the digitally controlled oscillators, then my original comment wouldn't apply.

I guess half the problem with many people's misunderstanding of the 3P, along with other DCO synths, is that they take a hybrid approach by mixing digital technology with analogue sound production. The lines get even more blurred when you bring in the likes of the Korg DW series, which flips things over by using digital waveforms for fully digital sound generation, and then using analogue filters and amps!

Hopefully the OP's problem was solved simply by changing the internal key velocity parameter!

On Tue, May 1, 2018, 5:39 AM Florian Anwander fanwander@... [kiwitechnics] < kiwitechnics@yahoogroups.com > wrote:

 

Hello Chas

On 01.05.18 01:43 , Chas D 350ypvs@... [kiwitechnics] wrote:

You can rule out a digital to analogue converter

Though I think, that the OP has different problem: That is not true. The D/A-converter provides everything for the sound control. For example the envelope for the VCA. If the D/A is broken, then there is no envelope or gate for the VCA and so there would be no sound.

Florian