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WOK
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2093 posts since 24 Feb, 2004, from Germany

Postby WOK; Thu Oct 16, 2008 8:09 am Frequency-Divider in Synthedit ?

Old organs and string machines had there polyphony built up from frequency-dividers, driven by one master oscillator. This gives all notes played the same phase.
How to achieve this in Synthedit? I want to build a stringmachine, but with a standard schematic in Synthedit (MIDI-OSC-VCA), every new key pressed will start another voice oscillator at that moment, giving a varying phase.
Someone knows how to emulate a frequency divider in Synthedit or make all the "simulated" OSCs of Synthedit running in sync?
novaflash
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2041 posts since 21 Nov, 2003, from Mars, Solar System

Postby novaflash; Thu Oct 16, 2008 8:23 am

re-synchronize waveform by sending an event to the "sync" pin.
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WOK
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2093 posts since 24 Feb, 2004, from Germany

Postby WOK; Thu Oct 16, 2008 9:00 am

novaflash wrote:re-synchronize waveform by sending an event to the "sync" pin.

Synchronize with what? If I use the GATE output, I have the same behaviour like before (a new phase on every keypress). I use only one OSC in the structure, Synthedit creates virtual OSCs "on the fly" when more keys are pressed - but these are not in the structure and so can not be connect to be synchronized.
novaflash
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2041 posts since 21 Nov, 2003, from Mars, Solar System

Postby novaflash; Thu Oct 16, 2008 10:11 am

ok i understand what you mean, effectively the method described is bad.
sorry, i don't know how to do that.
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jupiter8
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9376 posts since 17 Sep, 2002, from Gothenburg Sweden

Postby jupiter8; Thu Oct 16, 2008 10:24 am

I don't see how you could to that in SE. The oscillators would be in essence monophonic and the rest of the stuff polyphonic. I really don't see that happening in SE i'm afraid.
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WOK
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2093 posts since 24 Feb, 2004, from Germany

Postby WOK; Thu Oct 16, 2008 11:16 am

My only idea is to eventually build a frequency divider with 12 synced OSCs - but how do I split up the incoming MIDI-events to the proper oscillator ?
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jobromedia
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4830 posts since 10 Feb, 2006, from Stockholm, Sweden

Postby jobromedia; Thu Oct 16, 2008 4:00 pm

I think SynthEdit does this allready. Just my thought.
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WOK
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2093 posts since 24 Feb, 2004, from Germany

Postby WOK; Fri Oct 17, 2008 12:19 am

jobromedia wrote:I think SynthEdit does this allready. Just my thought.

OK, to make the problem more clear, here is an .SE1 example:
http://www.service-1.de/music/Pitch_Divide_2.se1
A MIDI-controlled OSC with a divider for sub-octaves.
If you press a key, the suboctaves are phase synced with the main OSC - BUT: if you press a note several times, or you hold one key and press the next one ocatave higher several times, you will here how the sound slightly changes every time, because there are phase cancellations.
In polyphony, Synthedit creates "virtual OSCs" on the fly but there waveform starts with the key pressed, so they are not phase synced.
What I would need for an emulation is a frequency divider that
generates all notes for the keyboard (in sync) and a MIDI-splitter,
that seperates the pressed key notes to open the VCAs for the matching notes.
Or is there a way to make Synthedit run all "virtual polyphonic" OSCs
in phase?
rexman77
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52 posts since 10 Oct, 2010, from USA

Postby rexman77; Mon Nov 01, 2010 7:06 pm

I've been thinking about this as well, and it's one of the primary reasons I haven't started working on a string machine yet. The only way I can think to do this without using some kind of frequency divider module (which I haven't found) is to have a midi-CV and oscillator for each key and midi-filter each one so that pressing a key only triggers one oscillator. Then, you osc-sync all of the lower octaves to the top 12 to emulate locked phase and run the whole thing through a single VCA and ADSR.

I had also considered trying to get a free "octavider" guitar effect VST from the web and trying to work with that, but SE's VST hosting is a little buggy atm.

I'm not sure if these would work as I haven't had the time to test them out my self, except for the individual midi-CV and dedicated midi filtering per key, which works well.
The only thing we shouldn't know is what we can't do.
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antto
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2499 posts since 4 Sep, 2006, from 127.0.0.1

Postby antto; Mon Nov 01, 2010 7:37 pm

custom MIDI processing and oscillator into the same module
i'll be doing this soon
also, (as in the NovaChord) the master osc (for every key) are divided into every octave and thus - there is 1 path for each note already running and one VCA for every note
thus it's not like activating/deactivating voices, the voices are already running at all times you just open the appropriate VCA to make the note "on"
It doesn't matter how it sounds..
..as long as it has BASS and it's LOUD!

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rexman77
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52 posts since 10 Oct, 2010, from USA

Postby rexman77; Mon Nov 01, 2010 9:02 pm

antto wrote:thus it's not like activating/deactivating voices, the voices are already running at all times you just open the appropriate VCA to make the note "on"


Yes, this is how transistor organs and, to some extent, tonewheel organs operate. A constant signal generation method for each key with the keypress allowing the signal to pass through to the amplifier.

Does anyone know what the circuitry for an octave divider contains? I think a custom module may be what we would need.
The only thing we shouldn't know is what we can't do.
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osiris
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7137 posts since 20 Nov, 2003, from Lost and Spaced

Postby osiris; Tue Nov 02, 2010 4:52 am

This is VERY CPU intensive, though. I think CK had a freq divider in one of his packs I got & I tried it to make a supersaw out of a single oscillator. Blew CPU through the roof. Even compared to supersaw made with 6 detuned oscillators.
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antto
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2499 posts since 4 Sep, 2006, from 127.0.0.1

Postby antto; Tue Nov 02, 2010 5:14 am

it shouldn't be so CPU hungry if you know how to do it:

there are 12 notes (keys) in an octave, so you need 12 oscillators to run at all times
then, when you need a "voice" you check which key this is, and divide (up or down) and feed to the amp
if you want to cover 5 octaves, this means you need 5*12 envelope generators with VCA, and any per-voice modules after that

also, when you have to play D#4 and D#4 is already playing or not yet released - you simply reopen the envelope, you don't generate a new "voice" like in polyphonic synths

it goes like this:
12 oscillators (at either the lowest or highest possible octave)
from there, you divide up or down to get one path for every other octave and feed that to the per-voice path

the "dividing" itself is:
1) the VCOs generate the lowest octave and you use modulo operation (divide by powers of 2)
2) the VCOs generate the highest octave and you use a frequency doubler (not sure about this, maybe there are such circuits but i wouldn't do that in DSP, it might be easier in the analog circuit)
;P~
It doesn't matter how it sounds..
..as long as it has BASS and it's LOUD!

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rexman77
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52 posts since 10 Oct, 2010, from USA

Postby rexman77; Tue Nov 02, 2010 6:31 am

antto wrote:1) the VCOs generate the lowest octave and you use modulo operation (divide by powers of 2)
2) the VCOs generate the highest octave and you use a frequency doubler (not sure about this, maybe there are such circuits but i wouldn't do that in DSP, it might be easier in the analog circuit)
;P~


I hadn't thought of starting at the lowest octaves and using a frequency doubler. Old string synths and transistor organs start at the top octave and divide-down. When you divide a waveform period or frequency, you get a lower note.
The only thing we shouldn't know is what we can't do.
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antto
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2499 posts since 4 Sep, 2006, from 127.0.0.1

Postby antto; Tue Nov 02, 2010 6:38 am

sure, but i wouldn't do that in DSP
as.. a high octave - you're already very close to Nyquist and aliasing/rounding erros and similar evil are strong there
using this to make lower notes would make it worse (unless you figure some smart way..)
going the other direction is easier
It doesn't matter how it sounds..
..as long as it has BASS and it's LOUD!

irc.freenode.net >>> #kvr
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