Australian company Cycle Instruments have burst onto the scene with a very interesting and highly ambitious debut, the Tetrachords sequencer. A substantial module at 36HP, the Tetrachords promises big: polyphonic sequencing over both CV and MIDI, four sequencer tracks that can work separately or together and bounteous options when it comes to customising scales and chords.
To best understand the Tetrachords’ philosophy, it’s worth taking a closer look at its name. The word ‘Tetrachord’ literally translates to ‘four notes’ and constitutes, for all intents and purposes, half a diatonic scale. Traditionally they’re bound by a perfect fourth — so the first tetrachord of a C major scale, for instance, is C, D, E and F, and the second is G, A, B and C. Of course, when it comes to modular, traditions are there to be broken.
The Tetrachords presents its workflow as two rows of four buttons. Depending on the selected mode — Arp or Chord — these represent notes in a sequence or notes in a chord. Alongside each row of four is an encoder for selecting one of six scales: ostensibly, with both rows set to the same scale and order, and all steps engaged, the Tetrachords will play through that scale from start to finish. I say ‘ostensibly’ because even at this rudimentary stage the Tetrachords starts to open its behaviour up to wildly variable customisation and performance.
Neighbouring Spread and Amount controls for each row can create octave leaps (of multiple octaves, if desired) and dictate the order in which these occur, labelled with little dots and lines and a little white LED meter respectively. A Reverse button switches the direction of travel; since there’s one of these for each tetrachord row, it’s possible to reverse the order of one but not the other. Ordinarily the forward motion of the transport is left to right on the top row (the first half) then left to right on the bottom (the second half). But a Path encoder on the right of the panel allows pretty much any route between these rows to occur: forwards then backwards, zig‑zagging between rows, hopscotching back to the first note of the sequence after each step, quasi‑random (with a re‑randomisation button) and more. If that’s not enough a Roland SH‑101‑inspired step‑sequencer mode allows user‑programmable custom sequences of up to 32 notes as well.
The Root encoder, with its handy ring of LEDs to show which notes are in play, can be used to change key or to change the starting note of a sequence within the confines of a scale. This might not sound particularly creative, but whistling through iterations of a sequence across one scale is essentially akin to creating chord progressions and is a fantastic compositional tool.
The last piece of the Tetrachords’ fundamental architecture is perhaps the most rewarding to play with, at least in the first instance. The Root encoder, with its handy ring of LEDs to show which notes are in play, can be used to change key or to change the starting note of a sequence within the confines of a scale. This might not sound particularly creative, but whistling through iterations of a sequence across one scale is essentially akin to creating chord progressions and is a fantastic compositional tool. It’s the closest thing I’ve come across to the tone‑row‑based workflow of the Eventide Misha sequencer, and if you have read my review of that module you’ll know what an accolade that is.
Now: all of the above applies when crafting one pattern. Above each of the eight main sequencer buttons is a little white ‘pill’ LED that represents the selected pattern, so program another pattern, or seven, and then use a pair of arrow buttons, or patch in some triggers, to cycle between them. In this sense, the Tetrachords offers a rather wonderful thing in an incredibly streamlined package: sequencing sequences. Fans of the Teenage Engineering OP‑1’s Finger Sequencer will be familiar with the creative delights contained in sequencing sequences — let’s dub it meta‑sequencing — and those delights are here in spades. Each pattern can have its own slew settings, play as a chord or a linear sequence, have a different order and the rest. I found particular reward in setting the lot to Chord mode and working through progressions in orders that I would never otherwise have thought of.
This leads us to the topic of polyphony: the Tetrachords can work over MIDI or CV, and interface between them, usefully. It has four tracks, all of which can work together or independently to various degrees. When using CV alone, these can be multitrack — that is, can output different sequences to different destinations — or they can be used to stack up to four oscillators polyphonically.
Whew! Fair to say the Tetrachords is a rather esoteric module on first impression, and in many ways its slightly congested faceplate doesn’t offer the most intuitive layout. This is a complex module, and it feels like not much has been done to mitigate that complexity or give much of a foothold. That said, spend a little time getting to know it and things get much more fluid. And after all, you might say it’s part of the territory with something so incredibly powerful. The manual, if you’re interested, is 167 pages long.
Interestingly, the Tetrachords has no onboard clock, which might come as a surprise. Instead it expects triggers, over MIDI or CV, which on reflection I think is a very good move. The message from Cycle Instruments is clear: this is a tonal, melodic module, and it’s ready to get to work with your other, rhythmic modules. In that capacity it truly excels, and Cycle Instruments have managed, somehow, to stretch the already well‑explored boundaries of sequencing in Eurorack. If this is their debut, I can’t wait to see whatever comes next.
£615
$795