One popular solution is the shift register, such as the Music Thing Turing Machine or as a mode in the Expert Sleepers’ Disting Mk. 3. These can certainly yield perfectly fine results – I use Disting’s shift register all the time. But what if you don’t have a shift register, or maybe want a bit more control over how the sequence behaves and evolves over time?
Over the next three months I’ll be taking a look at what has over time become the basis of my entire rack. I’ve dubbed it the Melody Machine: a “sequencer” that does its job using a phase-resettable LFO fed through a quantizer. Adjusting the LFO’s frequency or shape changes the melody, while resetting the phase every, say, 8 steps fixes the pattern to that length. This month I will cover the basic ingredients you need for the patch. Next month we’ll go over items you can use to further control (or lessen control if you prefer) your
sequence, and after that we’ll conclude with a rather involved two-voice patch taking
advantage of the technique to generate both a bassline and a higher sequence.
What you need
The basic elements for a Melody Machine are for the most part pretty common in Eurorack, perhaps excluding the quantizer. They are:
•A clock. For the most part, a sequence isn’t much of one without a rhythm. Pretty much any old clock will do – the clock out of a “real” sequencer, a channel of Maths, you name it. I use ALM’s Pamela’s Workout.
•A clock divider. To make your sequence repeat, you need some way of resetting the pitch (that is, the LFO) after a fixed number of steps (generally 8 or 16). Suitable modules include 4ms’ Rotating Clock Divider, the Doepfer A-160-2 and the Make Noise Tempi. My Pamela’s has several channels that can function as clock dividers, so I stick to that.
•An LFO. The backbone of this machine, your LFO will generate the initial control voltage that will, after some processing, become the pitch of your melody. Some way of
CV-controlling the LFO is a bonus, be it frequency or waveshape. As hinted at above, the LFO must have a “clock,” “sync,” or “trigger” input which resets its phase. This excludes the ever-popular Maths but does include many others, including the Mutable Instruments Peaks, Xaoc Devices Batumi and Doepfer A-147-2. I generally use a Mutable Instruments Tides with the Sheep firmware, but occasionally I’ll use a Pulp Logic Cyclic Skew despite its lack of frequency CV. I’ve also used an Intellijel Dixie II+ but found its reset input kind of wonky in that the waveform will sometimes start going downwards after a reset rather than
upwards, in a way I haven’t figured out how to control.
•An attenuator/offset module. The output of a typical LFO is 10 volts peak-to-peak. In
Eurorack-land, this translates to 10 octaves, which is far too large a range for most sane melodies. Further, you probably also want to constrain where in the musical scale the
sequence takes place, such as A to A or D# to D#. For this, you need some sort of
attenuating-and-offsetting module. Items fitting the bill include the Intellijel Triatt, Mutable
Instruments’ Shades or Blinds, and Befaco A*B+C. I have a couple little Pulp Logic Att-Off tiles right under my tiles for the job.