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Key Appropriate Pitch Spreader

Like a Clock Divider, only musically, for pitches
  (+6, -1)
(+6, -1)
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There's a particularly interesting group of instruments called Modular Synthesisers that lies directly within the intersection between electronics, signal processing, music and crazy. Some folks create self-evolving musical compositions that require nobody to play by wiring up complex racks of blinking hardware, others craft interestingly modulated space-noises or clinically obese beats, the likes of which are normally found only within the minds of deeply disturbed psychedelic warlords, long since disappeared into smoke.

Basically, various bits, or modules, are patched together with wires, so perhaps an oscillator is wired so that the flat amplitude of a basic waveform is modulated into an envelope, filtered to round out the sound, and triggered on receipt of a pulse from an expensive bit of kit called a sequencer.

A sequencer is a thing that triggers pulses in sequence, each of which can be used to play a note. A note who's pitch is controlled by a twiddly knob. Put a bunch of notes in sequence, and there you go, you're Mozart, tunes and stardom await.

A cheaper version of a sequencer can be created using a thing called a Clock Divider - basically, you send in a clock signal, a series of ticks, and the divider will send out a pulse on say every 1, 2, 4, 8 and 16 steps each pulse generated on a different output. Plug in voices on say 1 and 4 - and you've got the basis of a simple 4:4 rhythm. Normally each voice has its pitch set - but comes at a price - and you don't want to have to set up multiple voices just to supply different pitches - some tunes can have up to 16 individual notes (ask Mozart) which in module terms would very rapidly break the bank.

So here is an idea for a modular synth module, designed to generate a song's worth of pitches (or at least pitch-control voltages) that could be patched into a single voice and triggered by a simple Clock Divider to create simple but cheap beats.

The module consists of the following inputs: CV In, and outputs 0, 1, 2, 3, 4, 5, 6, 7. Additional controls include: A fine-tune pot, a {flat, regular, sharp} 3-position switch, and a {regular, 5th, 7th} 3-position switch. Optional extras for the delux version might include individual off-key modifier switches {flat, reg, sharp} for each output - but let's concentrate on the basic version for now.

So a control voltage goes in, and populates the outputs with chromatically pleasant output voltages according to the scale switches which define the musical key being generated. Each output 0 through 7 (or whatever number is deemed appropriate) can then be used as the pitch-control for a subsequent envelope/modulation thing.

Another way to think of it might be as a temporally parallel arpeggiator.

zen_tom, Oct 29 2015

Appropriate elevator music https://www.youtube...watch?v=YP_XG08JHyw
[FlyingToaster, Oct 29 2015]

Wilsonic http://www.synthtop...crotonal-harmonies/
review [Ian Tindale, Oct 30 2015]

Scalegen http://www.gestrument.com/scalegen/
[Ian Tindale, Oct 30 2015]

A recent project of mine http://mitxela.com/...everse_oscilloscope
[mitxela, Oct 30 2015]

A basic mock-up https://s3-eu-west-...ber/chordsource.png
Here we see the most basic configuration - basically, you set your starting frequency with the pot, dial in the key variables (major, minor, 5th, seventh etc) and calibrated output voltages are generated over ports 1-8 [zen_tom, Oct 30 2015]

Erv Wilson http://www.anaphoria.com/wilson.html
[Ian Tindale, Oct 30 2015]

(?) The Sonic Sky: Intro https://vimeo.com/29632431
must see [Ian Tindale, Oct 30 2015]

My tour of my Korg Mono/Poly https://www.youtube...JWaTJ7H1VBWGwX5effS
This week I have been mainly shooting and editing this video series, which is fairly synth educational as well as to do with the Mono/Poly itself. [Ian Tindale, May 22 2016]


       will it fill in the holes in my road>
po, Oct 29 2015

       I'd like the 2 people who bunned this to explain what the hell it is.   

       It sounds like you're going at something totally sideways, which I'm normally all in favour of when I understand it.
FlyingToaster, Oct 29 2015

MaxwellBuchanan, Oct 29 2015

       I await enlightenment.   

       And here's a little something while you wait <link>
FlyingToaster, Oct 29 2015

       You're talking about a modular analog sequencer with an insert point, bypassing internal/external clock or stepper, for direct playing of slots ? (even perhaps, output an average of 2 slots if the input voltage is between the voltage stepping)
FlyingToaster, Oct 29 2015

       Synthesizer technology of some kind...
RayfordSteele, Oct 29 2015

       I know a bit about modular synths, but nada about their sequencers.
FlyingToaster, Oct 29 2015

       The CV in, would that be to shift the whole sequence to a different key?   

       One of the best bits about control voltages in synthesizers is that they're logarithmic (usually one volt per octave), so if you take twelve identical resistors and place them in a line between a one-volt source and ground, you'll get an equally tempered chromatic scale on each of the connections. If you strung the resistors between your (buffered) incoming CV signal and a summing amplifier fed by the CV and a one-volt source, the whole octave would track the incoming pitch. Then just feed them all into your sequencer.   

       Switching in different resistors should be able to sharpen / flatten individual notes.
mitxela, Oct 29 2015

       The limitation would be the selection of the tonality intervals.   

       The description sounds like partly a description of a top-octave divider, which is the technology used in a lot of ’70s and ’80s string machines. The octave at the top was defined as separate polyphonic sources, the other octaves were divided down from that.   

       However, the description also describes beat division in a sequencer, much akin to a drum machine.   

       But what the description really results in is a polyphony generator that produces a set of intervals from an incoming control voltage signal. This is possible (typically by dropping down from the highest note), and in a modular you’d use an attenuator module (which really is as simple as it sounds — just a variable resistance). However, you’re restricted as to your a] number of notes (but you could build more attenuators) and 2) specific scale at any one time.   

       A better approach would be to use actual sequencers — many of them at once — to drive individual VCAs each individually scaled which drop down the voltage, allowing different intervals per sequence step. A further complication of this (and expense) (and therefore impressiveness) is to use a set of sequenced VCAs to drop down a further set of differently timebase divided sequenced attenuators/VCAs, thus making each step contingent on the steps of the first set. Thus, you could produce quite evolving soundscapes that pretty much don’t repeat exactly within the space of a piece of music (possibly not even within the same month).   

       But yes, all it amounts to is a set of parallel attenuators dropping down the highest CV to generate all the intervals in a scale. If that’s the case, I’d say what about c} changing the scale dynamically, and 4: what about microtonality?   

       I’ll put in a few links to a couple of iPad apps I use for microtonality experimenting in (which is always a good excuse for when people erroneously expect I’m working in a rigid and existing established boring accepted idea of a scale).
Ian Tindale, Oct 30 2015

       Did he just invent the DCO ?   

       sorry [zt] I can't seem to parse what you're going on about.
FlyingToaster, Oct 30 2015

       Not really, a Digitally Controlled Oscillator is not necessarily polyphonic in itself, merely integrates a DAC to allow computerisation of the sending of the notes as a byte rather than a CV, but the rest of the oscillator to be an actual analogue oscillator. They were a useful intermediary step (my Korg Poly-800 uses DCOs, but internally is mostly an analogue synth once you get past the computer control of all the parts) (well, I say ‘computer control’, you have to imagine the state of computer based products in 1983!). The DCO allowed a bit more stability and predictability in tuning (in theory — the oscillators themselves could still have drifted). Soon, however, the whole of the synth would become a digital emulation (typically by populating a wavetable either once or frequently (depending on the patch) and continually reading out the values, or by abandoning the subtractive model and going for FM, or by integrating pre-sampled ROM sounds giving rise to sample + synthesis techniques as in the more popular of the ’90s synths in most of the dance music of the era).
Ian Tindale, Oct 30 2015

       I'm pretty sure DCO's count ticks for oscillator timing.
FlyingToaster, Oct 30 2015

       Not in the ones I'm referring to, for example, in the Poly800. It’s literally an oscillator, controlled digitally (often using a resistor ladder DAC) and without the digital control it would free run by itself. But yes there are others that use a pulse train and wave shaping to become an ‘oscillator’.
Ian Tindale, Oct 30 2015

       The evolution of the DCO is a bit diverse, and by definition anything that was a controlled oscillator, not voltage controlled, but using some kind of digital control, counted as a DCO. The first and most obvious way was to simply bolt on a ladder DAC to an existing VCO design. This was preceded by the “Computer Controlled” sequencers such as the Roland CSQ-100 (had one of those) and CSQ-600 (still have one up in the attic), which used ram to store a voltage value in actual digital bits. I used mine on my Roland SH-09 synth (still have that, too). What came into it and out of it was ordinary control voltage (CV) though — the user never saw the ‘bits’. Bring the sequencer and synth together in one module or board, and you have what could be termed a DCO. Just as drifty, but more storable and sequence-able.   

       Other methods were to take the same type of tech used in string machines (and organs), the digital top- down divider. Giving out such a pulse train allowed greater polyphony but unless you wanted the sound of a pulse wave (which you might if Grime and Garage had been invented back in the 1970’s in Japan instead of in 2000’s London) you’d have to wave shape the pulse into something more like a sawtooth. This is an interesting distinction, as it is far more difficult to generate a pure sine or triangle from an incoming pulse train, but less so for a sawtooth, so a lot of the digitally controlled era only offers pulse and saw waves (e.g., a TB-303).   

       As I mentioned, the next step was to create the waveform once and put it into a small quantity of memory and simply read it out of memory at the rate corresponding with the pitch(es), and once we got to that stage, there was literally no need to have a real oscillator at all.
Ian Tindale, Oct 30 2015

       Not midi-ish. Not even timing related, really. Just a thing that you put a voltage into, and get eight other voltages out of (or the original plus seven others). The intervals between all voltages are musically related (assuming an 1V/8va VCO input (one Volt per octave)).
Ian Tindale, Oct 30 2015

       Great comments guys, I think it's going to be easier to explain by taking concepts each of you has identified and tying them all together.   

       [mitxela] yes, the CV in would allow for modulation of the key whose default value would be dialled in via the pot. Plus, loving the fact that you're already considering the circuitry!   

       [Ian] yes, I'm thinking of a polyphony generator, whose default is set by pot/cv adjustable source, and whose intervals are defined by the combination of two 3-position switches whose purpose is to pick different sets of locations from (I suppose) 16 possible semi-tones. I think I might need to change the initial 3-position switch from {flat, regular, sharp} to perhaps {Octave, Major and Minor} with the second one identifying sub-types of those three, resulting in a combination of 9 different pattern-sets.   

       Each of the voltage outputs would be constant, so we would expect to feed them into one or more oscillators as a tuning signal. An alternative might be to feed them into some kind of multiplexer, controlled perhaps by a Clock Divider signal. Gate and/or envelope would be triggered by a copy of the Clock Divider signal (or piped through the associated multiplexer) The multiplexer part is probably an idea for another day though! The main application I have in mind here is to create a relatively cheap sequencer alternative. In terms of the tonality component, I can't help feeling that something like this must already exist, but I've not found it yet. The simplest application would be to perform chord/chorus via driving multiple VCOs.   

       [Ian]'s idea of changing the scale dynamically, I like. Either by optionally feeding some gate inputs (3 of these would give us 8 options, which might be enough, and 4 gives us 16, which may be too many) or replacing the pair of switches with an array of options, and using a trigger signal (and manual toggle button) to step through each of the possible options.   

       I'm not sure I'm entirely ready for microtonality, I was thinking for special non-standard scales, we could add a 3-pos switch for each output, allowing adjustments for each output by semi-tones up or down.   

       I'm going to try and draw up how the plate might look, and maybe a possible patch arrangement to put it into context.
zen_tom, Oct 30 2015

       You may be interested in an electronics / synthesizer project I made recently. A few months ago I started playing with a chip called an ATtiny85, which costs 90p, and I wrote a square wave midi synthesizer for it. It's basically a midi-controlled-oscillator. It has an arpeggiator, pitch bend and modulation, and is small enough to be powered by the midi signal itself.   

       I used this midi-controlled-oscillator, combined with a ripple counter and a multiplexer, to build a very low resolution midi-controlled arbitrary waveform synth (link). It's great fun. It has many similarities to a sequencer. The whole thing cost maybe £5 in total.
mitxela, Oct 30 2015

       k, so ...   

       CV comes in one side,
it's split up and goes to the different pots,
the pots attenuate the voltage,
each pot sends out a CV.... all lower than the original which sucks.

       So add a global offset voltage at the input stage, equivalent to half the pot attenuation, so you can get outputs higher or lower instead of just lower. Or futz around with 8ve switches   

       And since the sequencer already has all those pretty pots, just sitting there doing nothing, and the only cosmetic change is giving individual outs to each stage...   

       (ya know at some point in time I really was capable of reading something and comprehending it, honest)   

       <reads the idea again>   

       Or do you mean a modular chorder, with enough twiddly bits that you can get perfect harmonic tuning (or other) out of it.   

       <and again, noticing "clock divider">   

       So the input CV is going to be (equivalent to) the fundamental of the output chord. A VCO which is controlled by the CV runs at a high enough frequency that it can be clock-divided down into all the partials, perfectly. These pulses are either used to run DCO's directly'ish or reverse-engineered into new CV's for VCO's and other nefarious purposes.   

       Like a one-note Hammond with a variable speed tone-generator motor.   

       Cool. Why didn't you say so ?
FlyingToaster, Oct 30 2015

       Clock divider is a red herring. There’s no clock involved to divide.   

       The chord intervalled set of voltages could be lower (easier) but also could be higher than the root note if instead of attenuators each used an opamp that tracked the input and output a constant offset. Either way, you have a set of voltages that are ganged to the input voltage.
Ian Tindale, Oct 30 2015

       I still think there's a divider in there somewhere.
Okay... if you want drawbar harmonics then you have
16 - divide the input CV by 2
8 - fundamental - the original voltage.
5 2/3 - multiply by 3 divide by 4 (or something like that)
4 - multiply by 2
et cetera.

       So no clock, just multipliers and dividers (no idea how that's accomplished, electronically)   

       nowait, that's linear.
FlyingToaster, Oct 30 2015

       I've put together (a nice brushed-steel) diagram in the links above. This unit really is about setting a reference voltage, and flicking some switches to get a series of tonally appropriate outputs. The basic version in the link is the static-interval version, though it does allow the starting pitch to be varied (modulated) via CV input.   

       The Clock Divider part is just me giving some context as to how/when you might use this module, setting the trigger of the divider to control when one or more voltages from this unit to pass to one or more voices - that's probably a more complex bit - the idea here is just to generate a pleasant set of voltages.   

       [edit] it's worth mentioning the links from others - the "Elevator Music" one from [FT] it seems I've watched before (enough to like it on YouTube anyway) and yes, it is quite proper. I've another couple of favorites on there somewhere which I might try and link in a bit. And I really like the Scalegen demo there, particularly the new-composition from old scale transformation, that's quite unique. And [mitxela]'s projects never cease to astound and amaze - I love the artistry, and honest write-ups, but can never get to the end before thinking "there must be money in this!" - and I'm quite sure there is. Particularly in the modular-component industry - run a few funky demos out there on YouTube and hook into some 8-bit, Moog, or other active fetish being talked about out there at the moment (be prepared to put in some soldering hours) and there's a few thousand to be made. I will solder for food if necessary (assuming you're not too bothered about messy/ugly joins!)
zen_tom, Oct 30 2015

       I’ve put in a couple more links all the way up there.
Ian Tindale, Oct 30 2015

       I’ve also put in a message down here, telling you that.
Ian Tindale, Oct 30 2015

       I put a perfectly pitched bun into your machine and got 8 harmonically resonant 1/16th buns out. [+]
absterge, Oct 30 2015

       zen tom; — have you seen the Intellijel Metropolis eurorack module?   

       By the way, I was a little inaccurate in my assessment of the Korg Poly800 as being a DCO synth. Last week I dismantled mine as it is now in a mode called “being dead” (needs a PNP power transistor and zener diode replacing) and I realised how it does what it does. It is quite an audacious design (in the bad sense of the word). The oscillator tone generation is all in one chip (followed by single analogue VCF and VCA). Not a synth chip, however, but a video game chip! The MSM5232 was designed for arcade video games. It has eight divide-down counters and bit shifters. I’ll have to do some more investigation on how it does wave shaping from an internally mixed set of square waves.   

       Also, I’ve posted a link up there to a ten part set of videos I made last week — a tour of my Korg Mono/Poly synth (be warned, it’s an hour’s worth to get through!).
Ian Tindale, May 23 2016

       Very nice, I watched one of the first ones where you demonstrate the tap-on/tap-off behaviour when the attack is set to zero, and thinking it was behaving quite "digitally".   

       These oscillator chips seem to have fanbases all of their own - I've seen multiple SID-chip (the SID was the sound chip from the Commodore 64) creations that generate a very distinctive sound indeed, and somewhere on teh intarwebs, I've seen a video someone's made of an electric bass-guitar whose pickups feed into one or more SID chips to create a stringed 8-bit bass-synth.
zen_tom, May 23 2016


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