[sdiy] Best AVAILABLE OTA for building new designs?

[Mattias Rickardsson]

Sounds like we are starting to overdesign things a bit here... :-D
Btw the "counting notes and keeping total volume constant" idea reminds me
of one of the Unison modes in Roland Jupiter-4, where you depending on the
number of depressed keys get 4-voice unison, 2x 2-voice unison, 3-voice
poly or 4-voice poly. The level loss in this mode is remarkable and not
very nice, especially when playing a 3-note chord and getting only 3 voices
playing compared to playing 1 note and getting 4 voces playing.

Anyway, I don't think the all-polyphonic voice summing issue should be too
over-thought, but just try to combine
- a summing where everything fits without clipping
- a level control that can gain even more so that clipping could occur but
a melody player would have enough output level.

One of the trickiest bits is that resonant filters make peak levels vary a
LOT more than you first might think, so you'll have to count with a peak
voice level that is much higher than many typical sounds.

Hopefully this is less of a problem in a true PS3100 voice where resonances
are very moderate. In the gainstaging of polysynth designs in general,
there is a huge advantage if you manage to keep filter resonances limited -
everything level related gets easier, but on the other hand it's hard to
make a firm resonance limiter without adding unwanted distortion or side
effects to the filter sound.

/mr

On Tue, 13 Aug 2024 at 08:49, Gordonjcp <gordonjcp at gjcp.net> wrote:

> On Tue, Aug 13, 2024 at 07:54:24AM +1000, Adam (synthDIY) wrote:
> >
> >
> > > On 12 Aug 2024, at 11:38 PM, Mike Bryant <mbryant at futurehorizons.com>
> wrote:
> > >
> > > I think you need to watch some videos of the late Keith Emerson.  He'd
> happily have twenty or more keys pressed on a Hammond, some of course held
> down with knives :-)
> >
> > David, you might be able to use this as a "feature"...  have a front
> panel control labelled "Knife Factor" that switches in a compressor with
> auto-make-up gain...
>
> Given that compressors work by controlling their gain based on output
> level - a negative feedback loop - I have this feeling that you could
> probably sum all the VCA CVs to give a "total output demand" voltage, which
> could be fed back to the DAC Vref (taking us back around to the multiplying
> DAC question) to depress the output voltage and keep the total level
> approximately constant.
>
> "Approximately" because you'd want it to have a bit of dynamics, you
> wouldn't want one note to be as loud as ten, but maybe five should be as
> loud as ten.
>
> --
> Gordonjcp
>
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