Organ Tone Wheel development.
Comments
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Yeah, that makes sense. Pretty much how that other guy explained it on that link. Your explanation is much clearer though. I'm having trouble figuring out the foldback by the way he explained it. I think the info is there but it's vague. Random clicks makes sense, I can picture that sound, I always thought the notes and partials were picked up all of the time but went thru a relay or a transistor before the signals were sent thru the drawbar faders. You wouldn't think the pickups close to the teeth would move. Maybe they did use relays because transisitors are too fast to create a delay. Whatever, the signal still kicks in at random parts of the waveform so that's another source of random clicking. I'll have a listen to your wav file later on my other computer, this laptop has a broken headphone out and I can't hear the clicks. This is much better than blending in a sampled click with each key.
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Sound good, nice job! So you have 91 oscillators running all of the time and it's only 15 percent cpu usage so you did something right. I could use some help though, I'm still trying to figure out the foldback system. So far, I've crossfaded an octave stretch back into itself. So if your playing single notes and walking up the keyboard in semitones it sound like your climbing up an octave which slower fades out and the octave below slowly fades in. So if you play all 12 notes in succession the last note you play sounds like the first note you play. It's not that simple because the partials do that but the fundamental remains unchanged. The end result is reduced brightness on the high notes of the keyboard but it's not like a filter it just shifts the drawbars back down during the climb which seem to thicken those higher registers without the irritating high notes. The low notes do the same only in the opposite direction, it keeps deep tones out of the speakers. I guessed the starting points for the foldback and used a slider to globally shift the starting points up and down. It's probably close enough for government work, doesn't sound bad but might be better if I understood how the foldback really works and how they did it.
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Foldback is dead simple. Its just a compromise in terms of the number of tonewheels.
Every key has 9 leaf switches.
When you press the key, the each of the leaf switches connects the output of a tonewheel to the main output mix.
For higher notes, the upper partials are not available as natural harmonics, because those tonewheels don't exist, so instead the switch connects to a partial an octave lower (or even two octaves lower). That's all it is. Dead simple.
For example, note 41 (an E) uses partials: 41, 60, 53, 65, 72, 77, 81, 84 and 89. They are all in the correct place - no 'foldback', because the highest harmonic required - 89 - exists as a tonewheel. (that 53 after the 60 is a separate issue kinda weird, but not foldback related)
If we look at note 43, it uses partials: 43, 62, 55, 67, 74, 79, 83, 86 and 91. Again everything in order… but now the top harmonic is 91 which is the highest pitched tonewheel in the system. So what about the following higher notes?
note 44, is the next one, and we know there isn't a tonewheel for the highest harmonic required, so what did they do?
note 44 uses partials: 44, 63, 56, 68, 75, 80, 84, 87 and 80… ooh, see how itt uses 80 twice? once in the 'correct' place, and once again in place of the 9th partial… THAT IS FOLDBACK!
the next 4 notes do a similar thing with the 9th partial being a repeat of the 6th, until note 48 where 91 is the 8th, after that the 8th and 9th partials are repeats of the 5th and 6th…
by the time we get to the highest note, note 61, it uses partials: 61, 80, 73, 85, 80, 85, 89, 80 and 85, so here 80 and 85 are both used 3 times… thats the maximum 'foldback'….
That's all it is, just a way to limit the physical number of required tonewheels. It's also a consequence of a manufacturing limitation. For the size of the tonewheels, they got to 128 teeth, and the jump to 256 was not possible due to limitations of their machining technology, so the last group only had 192 teeth, and those very high partials are already tuned less accurately as a result, they couldn't go higher even if they wanted to without being so far out of tune that it would sound terrible (unless they redesigned the whole thing with larger wheels… and it was already massive and very heavy).
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Ahha dead simple, they used what they had and it ended up sounding fine or at least better than missing harmonics. In a way that does fatten up those high notes. Thanks
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I just posted a beta version of a more complete hammond model in the User Library - it doesn't sound just like the real thing :), but is capable of some nice noises. Also doesn't sound the same as Chets version, so maybe better or worse for certain things.
https://www.native-instruments.com/en/reaktor-community/reaktor-user-library/entry/show/15399/
Comments and suggestions welcome.
And sound examples would be good from a competent player. I'm no keyboardist!
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I like the split point, might come in handy with bass pedals. Crossfading between the two might work out good with a single keyboard. Maybe give the spread of the crossfade a variable distance. Maybe crossfade each drawbar with it's own crossfade setting instead of a global crossfade.
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The way the split point works is that any input note below the split value acts as if it was played by the lower manual and left set of drawbars, any note equal or above acts as if it was played by the upper manual and right set. The transpose is so you can choose an octave, then with one medium sized midi keyboard, you can play bass and treble, both with different settings.
The 'percussion' mode only applies to the upper manual (just like the real thing), so you can hold notes below the split, and when you play notes above, you still get the percussion effect even though it is a paraphonic envelope.
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Yeah, it's good for small keyboards like it is. No complaints, I guess if you had an 88 note keyboard then crossfading on the sides of the split point might help. Mabey just turn down the overtones on the low side only. Then as you walk up the keyboard and leave the bass area the high tones will fade in as you approach the split point. This way the upper notes will sound brighter than the low notes and have a fairly smooth transition around the split point.
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Quick mock-up for a GUI base. The big empty space will eventually be a lot smaller, height-wise, depending on the lay-out of the toggles / controls / graphics. In the end the GUI should be more rectangular as a whole.
Happy to continue working on it, if you like.
Greets,
Bolle
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That looks great!
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kinda late to the party here but how much of the 91 voices are getting utilized to get sinewaves spanning multiple octaves?
because phase locked sine octaves are freeeeeeeee and with none of the hassle of divide down
one low frequency sine as the base you simply square and subtract to double the frequency. rinse and repeat all the way to the ceiling0 -
The ensemble actually has 91 voices. That's the exact amount of pickups in the organ. So basically when you play a note, every tone is available. That's pretty nice because the entire keyboard is polyphonic and you can play as many notes as you want. That was Chet's doing there. I think each voice is what is pickup up as the tonewheel turns. So it's basically 91 syncronized sine waves running all of the time. It runs about 15% cpu on my machine. I haven't analyzed it yet but I assume the octaves are all attached to the same ramp. They probably use a flip flop to divide the clock by two followed my more to get all octaves. Adding them all up makes 91 simultaneous tones. That's perfect for an organ otherwise having say 10 voices running for 10 note polyphony; the octaves rarely stay in sync and you will never know what you'll end up with when you play octaves on the keys. If that makes sense.
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It's possible that there are some nice optimisations available, but maybe not quite so obvious.
The current model I'm using is single drive motor with some modulation, so not completely smooth… into the gearing ratios, so that modulation from the motor effects individual tonewheels differently depending on their gearing. It acts like parasitic FM.
(in a Hammond, the drive motor generates 6 drive pulses per rotation, not a smooth/regular drive torque, this is damped by springs)
It might still be possible to optimise somewhat, because many of the gear rations are re-used. Really not sure though.
However there is more 'context' to consider…
The drive modulation is currently complete guesswork, and simplified to a sinusoid, the reality of the spring damped pulsing motor is likely to be more complex than a sinusoid FMed by another sinusoid at 6x frequency.
There is also a per tonewheel 'wobble' factor that is a randomly selected amplitude modulation to model the slight imperfections of construction and material that mean no tonewheels are completely 'true'
There really is no point in building a simplified model based on pure sines, there are loads of them in the UL, and even more in VSTi format.
I think maybe the biggest opportunities for improvement are the frequency response curves (in the pre amp and the per tonewheel resistances), and the scanner model which is really nothing like the real thing.
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One other area that would be easy to implement, but difficult for me to test is velocity based variation to the key click.
The key click is predominantly a combination of switch bounce, and slight timing variation between the switches for the individual partials for each key… pressing slower/softer causes the klick to be longer because it exaggerates the timing difference between the different switches.
It's modelled in a way that makes it easy to implement the variation… the problem is that I can't play hammond licks on keyboard, so I can't tell if I'm getting it right or not… so no point really :)
I think this would be noticeable to a player doing all those virtuoso atonal hits and glissandos that hammond players do.
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You can get fairly decent mid files online. This one has it's own separate organ track, same with the other instruments. https://freemidi.org/getter-13293
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