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

[sleepy_dog at gmx.de]

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 
> <mailto: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 
> <mailto: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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