The previous version can be found here.

The name of this module is a play on its function. Put simply, it generates a series of semi-random or themed stepped control voltages, or if you prefer, white and pink control voltages. The pink function is probably better known as 1/f, and thus the name of “1l/lfinite melody”.

Assuming a 1 v/oct VCO is being driven by the module, in the 1/f mode, the size of a pitch step is inversely related to the frequency at which it will occur. In other words, the smallest steps are most common, steps twice their size occur half as often, and so on.

As well as the 1/f mode, it has a pure random mode, where no weighting is put on the selection of notes. A large step is as likely as a small one.

As well as having these two modes of operation, there are 4 CV outputs available. With the exception of the fourth, each successive output is a shifted version of the previous. In random mode, this is very much the same effect as produced by an Analog Shift Register (ASR), but in 1/f mode, it takes on a whole new feel, as each of the six shift registers involved shifts at a different rate, according to the 1/f weighting. As such, the second and third outputs are related to the first, but not identical to it. The fourth output is subject to the same shifting weighting according to the mode of operation, but instead of driving a D/A converter, it drives a bank of knobs, allowing harmonic relationships to be set up.

And if that wasn’t enough, the randomness used by this module is obtained externally, from a regular white noise generator, or other varying voltage source, allowing more structured themes to be created. The random values are loaded in series at a rate determined by an external fast clock. This can simply be a spare output of a VCO (even one in use playing melodies etc.) or it can be deliberately controlled, or slowed right down to gain even more effects. The sensitivity of the random input can also be controlled via CV, again giving more possibilities.

See Diatonic Converter for an alternate output for this module.

A little on how it works:

First, a very simple theory lesson – 1/f implies a weighted ratio between a level and its corresponding rate. A change in level of 1 will occur at the clock rate. A change in level of 2 will occur at half the clock rate, a change in level of 4 will occur at a quarter of the clock rate, etc., thus giving rise to the 1/f ratio. This means the larger the step in output level, the less frequently it will occur. On the other hand, random implies exactly that – there is no determination of how great a step will occur – any step size is as likely as any other.

As is shown in the schematic, the Infinite Melody consists of several distinct sections.

The first section is the clock and random or 1/f selector. The clock and reset signals are processed by the LM358. When the 1f/Ra input is LOW (below about 2V), the reset line of the 4024 will be held LOW, allowing it to count, and clock signal connected to the second input of each EXOR gate via the 10k resistor will be blocked by the forward biased diode. The output of the counter is then fed via the EXOR gates (inverted in the process) to the clock inputs of each of the 4015 shift registers. Each successive shift register receives it’s clock at half the rate of the one above it.

When the 1f/Ra input is HIGH (above about 2V), the reset line of the 4024 will be held HIGH, forcing all of the outputs of the 4024 to LOW. The clock signal connected to the second input of each EXOR gate via the 10k resistor will pass as the associated diode is now reverse-biased, and no longer blocking the signal. The clock signal is now fed via the EXOR gates (inverted in the process) to the clock inputs of each of the 4015 shift registers. All shift registers are now being clocked at the same rate.

The second section of the schematic is the random number processor. Each shift register in the chain requires a random level to be present at its data input when it receives its clock signal. Traditionally this would be achieved by having a series of six independent random number generators. Instead it was decided to clock random data in serially at a rate significantly higher than needed. This section is essentially identical to the Gated Comparator, so I suggest you investigate that article for more information on how it works.

The block diagram of the Infinite Melody.

Construction

Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.

When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC sockets if used, then moving onto the taller components.

Take particular care with the orientation of the polarized components, such as electrolytics, diodes, transistors and ICs.

When inserting the ICs in their sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.

The master level pot for the mix-out is optional. It can be omitted if the resistor marked 27k* is installed. If using the pot, do not install the 27k resistor.

Euro rack users can cut the PCB along the row of holes, and double the board back on itself. You will need to install links between the two parts of the PCB. Pads are provided for this. There are two mounting holes that match on each board, allowing them to be secured to each other.

Pad identification

Notes:

• This module will work on +/-12 volts.
• Make sure you use a standard 4000 series CMOS, not 74XXX4000 series, e.g. CD4015, MC14015, HEF4015.
  Markings such as HC4015, HCT4015 imply 74HC4015 and 74HCT4015 and are unsuitable.
• If you don’t care about power-rail noise, just use a link instead of the ferrite beads.
• PCB info: 6″ x 3″ with 3mm mounting holes 0.15″ in from the edges.
• Please email me if you find any errors.

Parts list

This is a guide only. Parts needed will vary with individual constructor’s needs.

If anyone is interested in buying these boards, please check the PCBs for Sale page to see if I have any in stock.

Can’t find the parts? See the parts FAQ to see if I’ve already answered the question. Also see the CGS Synth discussion group.

Eye started experimenting with generating random MIDI data ages ago
Recently some Wiggler posted topic thread searching for True Random MIDI
Therefore challenged myself as a fast refresher project

virtual static x2
VCO/LFO
BPM Sync LFO 8b to /32 range
my original white noise method kept crashing sampler causing hard reboot error
plus added external gate option
so it can be manually played or sequenced for Kaotic midi noise Blasts
no clue if that’s what you were saying
works for me

Eye will record some demo tracks when have extra time
made multiple versions
one that is safe for hardware samplers… doesn’t cause machine reboots
another that prime for using Midi CV/gate…. high speed midi bursts
The extreme Sampler crashing version is getting stuffed with features
such as 32b to 1/64th note host clock sync LFO
White & Pink noise Wave options
plus anything else that was forcing hard reboot on my Ensoniq sampler
because it works awesome with VSTi & MIDI to CV/Gate
Time for recording more Kaos Midi Fire Experiments!

heres some schematics for the comparators. type 1 is used for sync processing. feed any h or v sync signal in, patch the outputs to the sync input jacks on some vcos, and twiddle the knobs and flick the switch till you get sync lock. easy. no pcb layout for these as i built them on stripboard.

type 2 grounds the negative side of the threshold pot, and takes the +V side through a switching jack, so you can insert an external signal to be used as the threshold voltage. useful for making a pwm squarewave or various other patches. both circuits have hysteresis controls to clean up the output a bit.

both of the above circuits are run from plus and minus 12 volts. the 3k9 pull up resistor means the output swings rail to rail, so it can trigger either of the 2 vco designs (one syncs on a -12 volt spike, the other on a +12) with ease.