[sdiy] String synth (solina) and Hammond organ questions

[Michael E Caloroso]

Using info pulled from the AH archives, I emulated the Solina chorus
ensemble effect successfully on my Korg SDD-3300.  Square waves from a
top octave combo organ system through a highpass filter (resulting in
a narrow pulse) completes the emulation.

Variations of that string ensemble effect can result in wonderful
choir ensemble effects.

MC

On 2/11/17, bill bigrig <billbigrig at yahoo.com> wrote:
> On the Solina, have you seen or heard about Jurgen Haile triple chorus PCB?
> It would give you some reference if you look it up.Rig
>
>     On Saturday, February 11, 2017 10:06 AM, "sleepy_dog at gmx.de"
> <sleepy_dog at gmx.de> wrote:
>
>
>
>  right, but no I won't forget that, it's on the list (and implementation
> ideas) :-)
>  And the percussion mode of course, is also on the list. That definitely
> adds some of the sound characteristic.
>
>  - Steve
>
>  Am 11.02.2017 um 17:09 schrieb bill bigrig:
>
>   don't forget key click. Rig
>
>       On Saturday, February 11, 2017 7:29 AM, Tom Wiltshire
> <tom at electricdruid.net> wrote:
>
>
>
>  On 11 Feb 2017, at 14:08, Gordonjcp <gordonjcp at gjcp.net> wrote:
>
>  > On Sat, Feb 11, 2017 at 11:42:18AM +0000, Tom Wiltshire wrote:
>  >>
>  >> On 11 Feb 2017, at 11:03, Gordonjcp <gordonjcp at gjcp.net> wrote:
>  >>
>  >>> What you absolutely must do is ensure that all the notes you generate
> start in phase.
>  >> <snip>
>  >>> This is something you'd need to do on a tonewheel emulation, too.
>  >>
>  >>
>  >> Why? The Hammond tone generator is free-running and the pitches are fed
> straight to the busbars. While the frequencies themselves might have a fixed
> phase relationship, it's not related to note onset in any way.
>  >>
>  >> Or am I misunderstanding what you meant?
>  >>
>  >
>  > Okay, pull out the 8' bar and play C3.  Holding that down, play C4, on
> and off a few times.  You'll hear it key on and off, great.
>  >
>  > Now pull out the 4' bar as well, and play C4 again.  What's the phase
> relationship between the fundamental of C4 and the 4' stop of C3?  Can you
> see a situation where you might end up with the two cancelling?
>  >
>  > If you were generating all 91 tones, you'd just be gating them on and
> off.  But in a typical software synth you'd generate each voice individually
> with fixed polyphony.  If you're not careful with it you could easily end up
> with some notes out of phase with others and odd random shifts in tone
> colour as a result.
>
>  Aaah! Yes, ok, absolutely! I see what you mean. Thanks Gordon.
>
>  This is a very good point he's making - since the Hammond uses the same
> tone generator for every/any note, there's no danger of phase cancellation.
> The same is true in the TOG organs/synths. Any "voice based" implementation
> needs to ensure that it copies this effect. This isn't too difficult if all
> the voices are produced on the same DSP, but it makes processor-per-voice
> implementations a bit awkward to do.
>
>  I'd be inclined to run NCOs simulating the correct Hammond pitches for the
> driving/driven gear combinations, and then use shifted versions of the phase
> accumulator to generate the waveform indexes for the required number of
> octaves. With only a dozen notes, that's not a lot of work.
>  To adjust the pitches for the standard TOG division frequencies would then
> be a case of tweaking the twelve frequency increments.
>
>  Tom
>
>
>
>
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