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Key Appropriate Pitch Spreader

Like a Clock Divider, only musically, for pitches
  (+6, -2)
(+6, -2)
  [vote for,

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]

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]


       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

       Did he just invent the DCO ?   

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

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

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

       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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