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

[sleepy_dog at gmx.de]

Ah, some interesting info on the waveform, thanks!
Btw., I already did this bottom-up oscillator plus "multiplicator 
instead divider" thing as this seemed to help easily / efficiently 
implement getting several octaves of phase-aligned sample indices from a 
waveform LUT.

- Steve

Am 11.02.2017 um 12:03 schrieb Gordonjcp:
> On Sat, Feb 11, 2017 at 11:44:53AM +0100, sleepy_dog at gmx.de wrote:
>> Howdy,
>>
>> so it's time to dig up one of the projects I started, and continue a bit ;-)
>>
>> STRING ENSEMBLE:
>> So, I programmed, in software, a at least not totally horrible Vox
>> Continental like transistor organ emulation.
>> I read that those Solina string ensemble things worked very
>> similarly. I know that one of the most important parts of the sound
>> was the chorus.
>> But before that: What was the sound source like? Did they also do
> Divider organ chipset, with the squarewaves passed through a highpass filter and clipped with a diode to only have positive-going peaks, generating a rather "narrow" sawtooth.
>
>> -> Where would I go from my transistor organ emulation to do the
>> string ensemble - what are the key differences?
>>
> What you absolutely must do is ensure that all the notes you generate start in phase.  In my string plugin I solved that by making a "bottom octave generator" and using that to set the phase of new notes - kind of the opposite of creating a top octave and dividing down.  This is something you'd need to do on a tonewheel emulation, too.
>
>> HAMMOND:
>> The other thing is, starting from the transistor organ, I made a
>> crude Hammond emulation, mainly by using only sine, changing the
>> tuning & drawbars, and making an extremely crude "leslie" effect.
>> (I'm not a DSP guy, so I first try to achieve some things without
>> getting really sophisticated)
>> But even without a leslie, from what I hear when I listen to some
>> hammond playing, the sound seems to be so alive, even single notes,
>> they seem to "breathe" somehow.
>> My software (not-really-)emulation sounds extremely sterile and lifeless.
>> Where does the variation in the hammond sounds come from? Is it
>> really that all the tonewheels are spring coupled, like I've read
>> someone speculate? I mean, all this mechanical (de-)coupling is
>> supposed to *prevent* irregularities due to the funky 1-phase motor,
>> right? I was thinking about introducing some slight phase modulation
>> in the clonewheels, but not sure randomly poking sticks in the
>> device is a good way to go forward ;-)
> The tonewheels are rigidly mounted to the shaft, and always have the same phase relationship.  If you're emulating this with a polyphonic synth you need to preserve that phase relationship when you create a new note, and the only real way I could make it work was with that bottom octave thing.
>
> Also, the output from Hammond tonewheels isn't particularly sinusoidal, but it's not far off :-)
>