Dave Smith Instruments Tetra - Poly Analog Madness for the Masses

January 1, 2010

Since releasing the Prophet ’08 (reviewed Nov. ’07), Dave Smith has been on the roll of a lifetime. His follow-up, the Mopho (reviewed Jan. ’09), brought massive analog sound to earth at a price almost anyone could afford, and still sells like hotcakes. Now, Dave has taken the monophonic Mopho, expanded it to fourvoice polyphony, kept the book-like size, and made the thing multitimbral.

Click here for audio example.


Big, fat, juicy analog sound. Direct USB control from computer yields very tight timing. Multitimbral mode means the Tetra is four Mophos in one box. Twopart splits/layers are savable per patch.


Four-part multitimbral mode is a global toggle, not per patch. Designing your own sounds from the front panel is a tad fiddly. No power switch.


$879 list/approx. $800 street, davesmithinstruments.com



0110 Tetra Main WEB

 Click image above for larger, numbered version.

1. Four dedicated knobs control cutoff, resonance, attack, and decay/release — usually the four most-tweaked settings in any patch.

2. These four knobs are freely assignable, and the factory patches do a great job of exploiting them.

3. What was a program/global switch on the Mopho now includes a third mode for the Tetra’s combo presets.

4. The “Push It!” button triggers sounds or sequences, and is flanked by a semi-circle of LEDs that indicate which voices are in use.

5. Tetra’s back panel ditches the Mopho’s audio input in favor of separate outs per voice, a Poly Chain connector for turning multiple units into one big polyphonic synth, and USB for connection to your PC or Mac.

6. An included universal AC adapter comes with plugs for every country — nice. Like the Mopho, there’s no power switch, so you unplug it to turn it off.


The Tetra is just a hair bigger than the Mopho, and side-vented for cooling. On the back are four discrete outputs for each of the voices. Outputs 1 and 2 are a stereo mix when nothing’s plugged into 3 and 4. There’s also a nicely-amped headphone jack and the wonderful Poly Chain connector for adding more Tetras (or Prophet ’08s) to increase polyphony. Tetra is also the first real analog polysynth to include MIDI-over-USB, and the timing is slammin’ — the improvement over using a regular MIDI cable and interface was especially noticeable when lining up Tetra sequences with parts recorded on soft synths in my computer. The USB port doesn’t stream audio, so you’ll need an interface to record Tetra audio into your computer.


As with the Prophet ’08 and Mopho, voices consist of two oscillators, a fully resonant lowpass filter, four LFOs, three envelopes, four step sequencers, and an arpeggiator. Oscillators. Each oscillator includes sawtooth, triangle, and variable-width pulse waveforms, along with a triangle-saw hybrid that sounds like a muted saw with a tad more beef. Like the Mopho (and unlike the Prophet ’08), each oscillator sports its own sub-oscillator, which gives it way more bass than the Prophet. There’s also a noise generator for whipping up whooshes and drum sounds.

You can hard-sync the oscillators for those metallic squawks the Cars made famous. Naturally, each oscillator includes coarse and fine tuning, but with an extra twist: oscillator “slop.” Turn this up, and the tuning drifts in real time for a more vintage analog sound. For more extreme pitch experiments, there are individual glide amounts for each oscillator as well. To ratchet up the heat even more, a feedback input in the oscillator section routes the audio from the left channel of each voice back into the filter section, and between the feedback gain and feedback volume settings, you can dial in everything from a touch of grit to a wall of filth.

Filter. This really defines the modern Prophet sound. Tetra’s filter is lowpass only, but it has two- and four-pole modes. In four-pole mode, it’s thick, warm, and creamy. In two-pole mode, it’s a bit buzzier, with more subtle resonance. There’s also an audio mod parameter that delivers FM based on the output of oscillator 1. This is great for everything from grit to squelchy ring-mod type effects.
Modulation. Three envelopes, four LFOs, four step sequencers, and a truckload of destinations make the Tetra extremely well suited for creating complex sounds with abundant rhythmic and tonal changes. Unlike some other analog synths, both vintage and new, the envelopes have a lovely snap to the decay segments, thanks to Dave’s care in designing their curves.

The four LFOs include triangle, positive or negative sawtooth, square, and random options, as expected. They can sync to tempo for rhythmic effects, which sound especially tight via USB. When the LFOs aren’t synced, their rates cover an extremely wide range, extending well into the audio realm, which delivers even more FM and ring-mod nastiness.

Step sequencers. These are a total knockout. Sure, they can embed TB-303- style note riffs in your patches, but that’s barely scratching the surface. Each of the four sequencers can drive almost any Tetra parameter. All the usual pitch, cutoff, volume, and pan options are present, but things get really interesting when you sequence changes to, say, pulse width, filter FM amount, LFO rate, or envelope segments. As if that weren’t enough, each sequence can have a different number of steps, so polyrhythmic madness awaits more adventurous players. Unreal.


With my Prophet ’08 and Mopho at the ready, I took the Tetra out for a spin to see how it handled. Comparing sound quality was easy, as all three units share quite a few presets. As mentioned before, the sound is identical to the Mopho, and when feedback or sub-oscillators aren’t involved, it’s the same as the Prophet.

Speaking of presets, the Tetra is packed with sounds ranging from legendary vintage patches like the ELP “Lucky Man” square wave glide and Van Halen “I’ll Wait” brass to modern, club-oriented sounds. These are equally satisfying, with stylistic emphasis on progressive, tech, and a smattering of electro-friendly patches.

Unlike the Prophet and Mopho, the Tetra also includes a bank of 128 combo patches, many of which are layered multitimbral sequences. Hit a key or the “Push It!” button and stand back — this is where the Tetra is in a league of its own. A sizable chunk of these multis are one-finger demonstrations of the versatility of this beastie, whereas others are massive unison leads. Click here for an audio example of this.

Each of the four voices can be its own independent synth, responding to its own MIDI channel, but only if the global multimode parameter is set to on. While we’d rather see this handled as part of each combo preset, that you get multitimbral mode at all in an analog synth at this price is tremendous. Plus, the limitation only applies to four-part mode; two-part splitting or layering (just like on the Prophet ’08) is available per patch.

0110 Tetra EditorTETRA EDITOR

Tetra’s editor (Mac or PC) makes designing your own sounds (or sequences) much easier than flipping through parameters on the hardware’s LCD. The LE version is included; a Pro version adds librarian features and other amenities for $39.99. At press time, both were standalone apps only, but Dave Smith is working on a plug-in version that’ll let you automate the Tetra from within your DAW.



It’s no secret that I love my Prophet ’08 and Mopho. Their sound has been a key component in almost every recent track I’ve done. The Tetra’s sound is every bit as deep, rich, and fat as the others. In fact, had the Tetra been available in 2007, I might have bought it instead of the Prophet. That’s not a knock against my baby, it’s just a testament to the Tetra’s unprecedented value. Any two-oscillator, polyphonic, true analog synth for around $800 would be a game-changer. One this good means that if you’ve been on the fence about buying an analog synth, there has never been a better time to jump. Dave Smith has hit another one out of the park — an obvious Key Buy winner.


Is it fully analog? Tetra’s audio signal path — the DCOs, filter, and amp — is fully analog. The LFOs, sequencers, and envelopes are digital, which allows for MIDI tempo sync.

Are DCOs really analog? Absolutely. Both VCOs (voltage controlled oscillators), and DCOs (digitally controlled oscillators) have analog guts, but voltage control is a tad less consistent than digital, so the latter provides better tuning stability.

What does the Prophet ’08 have that the Tetra doesn’t? Four more voices, lots more knobs, and (except for the rack version), a keyboard.

What does the Tetra have that the Prophet doesn’t? Sub-oscillators and a feedback loop back into the filter, so its sound has a bit more meat on its bones. Also, the Prophet is only twopart multitimbral; the Tetra is four-part.

How does it compare to the Mopho? Since the Tetra is basically four Mophos in a box, the sound is identical but the flexibility is vastly increased. On the downside, the Tetra omits the Mopho’s external input, so you can’t process external audio through it.

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