Sonic LAB: DSI Tetra Four Voice Analog Synth

US Dave Smith packs the voice of the prophet X4      10/11/09

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    MP4 12:6 mins

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Tetra Pack

Dave Smith continues supply the world of synthesis with his wonderful machines with the release of the Tetra - which can be seen as either  four times a Mopho (I guess that would be a really Bad Mopho), or half a Prophet '08.

The form factor is pretty much identical to the Mopho, with LCD display,  four assignable rotary encoders, plus the five fixed assignment knobs: Pitch, Cutoff, Resonance, Attack and Decay/Release for shaping the basic characteristics of any sound. You've also got the PUSH IT! button surrounded by four orange LEDs for voice trigger indicators. Perhaps seen as gimmicky initially, this button is supremely useful for triggering  program voices (4 banks of 128) and especially Combo voices (1 bank of 128) where it can fire off an entire four-part sequence.

Connections are:  13-15v DC in, USB - for software editor and direct MIDI via the computer, MIDI in and out and a Poly Chain Out - this is for linking up voice expansion to another Tetra, Mopho, or even a Prophet '08. Four audio outs  and a dedicated phones out complete the picture. You'll notice that the Tetra does not feature any audio inputs for external processing.

There are six additional small buttons for inc (+) / dec (-) - also for Bank switching, Program/Combo/Global select, Write, Assign Params - for the four rotaries,  and Edit B/Combo - this one toggles between layer A/B params when in Program mode and steps through voices 1-4 when in Combo mode.

There's plenty of DSI synth goodness here, with the tastefull combination of two digital oscillators with 1 and 2 octave Sub oscillators respectively,  and true analog filters - courtesy of the Curtis chip, as found in many synthesizers from back in the day. It is worth mentioning that while the Curtis chip has a long history, it wasn't in some of the most sought after synths of the time, in fact it generally appeared in budget offerings, although it is true analog, it's not the beefiest of filters.

Three envelopes (VCF, VCA and assignable) envelope three can be used in trigger mode to provide an extra LFO function, should the four dedicated LFOs not be adequate. Eight modulation routing/matrix slots complete the basic building blocks. Each program comprises of two layers A and B - these can be split or layered on the keyboard, each layer is  complete Tetra voice. Each layer also has its own independent, four channel 16-step sequencer which really hots things up, with incredibly complex and sequencey possibilities. These are very ably shown off with the on-board programs and combos programmed by some kind of synth genius as far as I can tell. Each sequencer can be run in sync or completely off on its own with beat divisions adding to the creative possibilities.

A (very) simple arpeggiator tops off the features, though its of little use compared to the sequencer, which can be transposed via the keyboard.

In Use
As you might imagine with a synth of this complexity in a compact desktop form, an external editor is pretty much mandatory - sure you can access it all via the front panel - but frankly, life is too short for that sort of thing, so the Tetra Editor - which comes as an optional extra - $39.99 for the pro version (editing and librarian) or Free for the lite version (editing only) is a must.

Initially, I found the editor to be fine and work well, but I did run into quite a lot of miscommunication, lock-ups and general unpleasantness which was kind of frustrating. It seemed to have no repeatability so I can't tell whether it was my setup (MBpro, 10.5.6) or the software. When it does work, it's fine and does the job admirably.

A La Mode
As well as the standard program mode - two layers A and B poly, unison and various combinations of those, there's COMBO mode - this combines up to four, single layer Tetra voices into a monster patch - its capable of some really complex stuff when all four sequencers are utilized. Additionally,  Multi Mode switches the Tetra into a four part mono synth with each part on its own MIDI channel for use with the sequencer or multi-keyboard setup or whatever. While this is a great addition, it's probably the weakest area of the Tetra with fairly basic implementation - you cant tweak individual sounds via the front panel - the assignable pots are disabled and the fixed assign knobs are global - ie: they affect the sound of all four parts simultaneously. It is only possible to edit individual voices params via an external MIDI source.

Another cracking little synth from DSI. Not mold-breaking, but a good variation on a theme. I would perhaps like to have seen a multi-mode filter for more sonic variants, and the software editor  was a less than wonderful experience for me. When confronted with a synth that has so much to tweak, that's what I want to do, and while at this budget, discrete control is totally out of the question, part of me yearns for a Tetra with knobs on - lots of em.
However, Tetra has a lot to offer the curious synthesist who wants poly AND several mono synths.

Available Now

RRP £549.99 / $879


$799.99 at

$799.99 at


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