Jan 26


Dave Smith who co-developed the DSI -120 integrated circuit that was used in the famous Prophet 08 in 2007 and the Mopho in 2008, amongst other achievements is also credited with the design of the award-winning small but powerful Tetra. The Tetra which has four DSI –120 circuits, provides us with an analog four-note polyphonic, four-part multitimbral programmable synth at a very affordable price.

The Tetra has a Polychain output so you could chain it to a Prophet 08 to make it 12 voice, or to Mopho to make a five-voice synth or of course to another Tetra to provide eight voices.


The Tetra is well packaged and comes with just the manual and a power adaptor with a generously long mains lead. It looks a sturdy piece of kit as you take it from the box, weighing 1.8 lb. (0.81 kg) (and with a size of approximately 8 x 5 inches). It has a bluish-grey metallic coat on its tough metal case and has 11 of those high quality black rotary knobs with chrome binding, similar to those on the Prophet 8 but smaller. These are used for Selections, Volume, Pitch, Cutoff, Resonance, Attack, Decay / Release and there are four assignable knobs. Eight of these knobs are the continuous type that are stepped for accurate setting of parameter values, while the Volume, Cutoff and Resonance controls are  normal and stop at the extreme of their travel. These also have a line on them so you know where your sound is set at a glance.

There is also the legendary “Push it” button included which has four back-lit indicators. This is basically a manual trigger for the Tetra that responds differently as to whether or not you are in Program or Combo mode. In Program mode, it can trigger a specific note at a specific velocity or a gated sequence, latch notes or sequences on and off, and manually step through a sequence. In Combo Mode, it cycles through the voices for polyphonic combos and plays all voices simultaneously when unison is on. Lastly there are six small buttons; a Selection button to select Program, Combo or Global, plus and minus to step up and down programs or parameters which can also be held to change banks, a Write button to write edited programs and combos, an Assign button for use with the four assignable knobs and finally an Edit B / Combo button which switches between program layers and in Combo Mode it is used to access various combo parameters. This leaves the LCD which is a readable blue back-lit LCD with 2 x 16 digits. Whilst this is clear for seeing the programs and combos etc, it is not really sufficient to carryout any serious editing. I would suggest you use the software editor for this. You can get a free editor for Mac OS or Windows with your purchase and download it from www.soundtower.com.


As I started to check the presets, my first impressions was “Wow”, these sounds really do damage your speakers. They have real squelchyness, phat and oomph! I recorded a synthy drum track into Sonar with a suitable acid bass sound. The Tetra recorded extremely well and the warm analog sounds contrasted perfectly against the clean digital piano that I added.


The Tetra has two Oscillators each with two sub-oscillators. Sub- Oscillator 1 goes down one octave and Oscillator 2 down two octaves. Both Oscillators have a variable waveform – Sawtooth, Triangle, Saw Triangle Mix and Pulse-Width. It has a Low Pass Filter with envelope, a VCA with envelope, a third envelope which has a useful repeat mode, four Modulators and four syncable LFOs. The Filter is a standard 2-Pole which can be switched to 4-Pole mode which means that it will self-oscillate. There are also two layers in the Tetra – Layer A and Layer B which you can stack or split across your keyboard. These layers can be used to great effect with the sequencer so that you can have two sequences running independently. This is best viewed on the Software Editor.


The preset programs are in four banks of 128 programs. The first two banks are identical to the Prophet 08. Each of the programs has two sound layers and can either have four-voice polyphony using two voices for each layer or can be played separately with editable separation points for each program. You will discover that the Tetra has all of the synthesis parameters of the Prophet 08 plus two sub-oscillators and a feedback loop. One of my favourite programs is:- Bridge Seq – this a loop and you can simply hold one finger down to let it play but I found you can create your own patterns by strategically taking your finger off stopping the loop and then make bass drum stabs between parts of the loop – great fun. The sounds are really classic sounds great phat basses, leads, analog strings, B3 simulations and great rhythmic patterns.

I remember reading in Sound on Sound magazine (and felt that what they had discovered was very unusual at the time) that although the Tetra had 512 programs, the 128 Combos that used programs did not take the programs from program mode but from an independent place within the Tetra. This meant that there were in fact 1024 programs. The good thing about this was that you could edit and change the programs as much as you liked in Combo mode and the 512 programs were unaffected. This is another one of those gems I wish all Synths had. Surely Dave Smith Instruments should have made everyone aware of this as a great selling point?


As I have already mentioned, there are 128 Combo presets and these make great use of the Tetra’s multitimbral capability, allowing four mono sounds to either be stacked in unison for massive sounds, stacked polyphonically or four different sounds and their sequences to be played via the “Push it” button. I love some of the Combos and they seem to sound very 70s/80s but also have an extra ingredient that adds a more up to date flavour.

Voicing Options

There are 14 voicing options in all on the Tetra for you to layer, stack and split sounds across your keyboard, 12 in program mode and 2 in Combo mode. This should keep you busy for quite some time. Obviously the maximum number of notes varies (up to a maximum of 4) depending on what option you choose.


Within Combo mode there is a basic arpeggiator that runs from 30 to 250 bpm. There are four basic modes –1) Up , where the Arpeggiated notes play in ascending order, 2) Down, where they play in descending order, 3) Up Down, where they play in alternately ascending and descending order and 4) Assign, where they play in the order in which they were struck.


I don’t know about you, but I love sounds that move and that is why I love the Tetra because it has plenty of modulations. It allows you to modulate almost everything in perfect sync with all the modulations controlled by the processor. There are four wide-range LFOs that are fully assignable and synchronizable to the internal or Midi clock and you will find all the normal waveforms – triangle, inverted sawtooth, sawtooth, square, and random. There are three fast ADSR envelopes with delay. The first two are assigned to frequency cutoff and volume. The third is fully assignable and can be looped.

The Tetra also has a modulation matrix with four connection options that allows you to route one of the 20 sources to one of the 47 destinations. The sources include LFOs, Envelopes, Midi controllers, and Noise. The destinations include the DCOs (pitch, volume, impulse width), sub-DCOs, filter cut-off and resonance, LFO parameters, envelope segments, and stereo width. You can also adjust the behaviour of each physical controller (wheel, pressure, breath controller, velocity, and footswitch) separately with one parameter in the destination list. The modulation matrix is great fun and I enjoy it here on the Tetra as much as I do on my Access Virus.


The Tetra’s sequencer allows you to program four tracks with up to 16 steps – just press the”Push It!” button and play. You can even proceed step by step with each keystroke. Each of the 4 voices has its own sequencer. Individual sequencer tracks can be routed to any one of the 47 destinations in the modulation matrix (for example: envelope, pitch, filtering, volume and position in the stereo field). Using VCA Envelope as a destination, for example will vary the volume of each step. You can mute a step and loop a track at any step of the sequence, regardless of the duration of the other tracks. This allows you to create complex sequences from a single program. Which means you can get four tracks of four sequences with four different sounds in multimbral mode – very impressive. The sequencer is a “gated” sequencer, so you will need to either play a note via the “Push it” button or via Midi so that your sequence can be heard. It will continue to play as long as you hold the note.


I expected the Software editor to be included on a disk in the box as it is a “must have” but you can download it easily and I suppose it does save on cost. The editor is very logical, well laid out and easy to use and it’s well worth having for your deeper programming needs. There is so much here to keep programmers happy with endless routing possibilities to bring the Tetra to life. When you make your own programs you really need to think about assigning controls that relate to your program to the four assignable knobs, so that it provides additional live control. In the past, I have found that depending on what you have created, this task can either be very easy or very difficult and sometimes you can create some fantastic controls to alter your sound live that you were not expecting to achieve.


On the connection panel at the back, you have four unbalanced audio outputs, a MIDI IN and MIDI OUT, the polychain connector (which doubles as a second MIDI Out) , a USB2 port and a power connector.

Interestingly you discover that the left Audio Output goes through a programmable-gain pre-amp which is controlled by the Feedback Gain parameter, then it goes through a VCA for feedback volume control, and finally to the filter input. You can get some great feedback, Distortion and Overdrive and make this baby “Scream”. If you turn up the Feedback Volume you will get varying amounts of the audio output mixed back in the pre-filter, individually per voice. I found that just small amounts of feedback produced the best results. When you try this I would suggest you start of with the feedback gain turned down and slowly experiment to find what you like. If you see the letters FB before the program name it means that this program has some level of feedback already programmed in.


This is a great little analog synth which is very portable and full of Prophet Charm. It is built like a tank, provides plenty of modulations, has some great filters and gives you a lot for your money including a very powerful sound that will shake your speakers. Its “crisp-sizzling” tops, real “punchy” mids and “down in your boots” low end, is just what everyone wants in an analog synth. On top of this, it sounds just like a Prophet 08 but it has the added Sub Oscillators and Feedback Routing, which makes such a difference. On the small negative side – it does not have a power button. This annoyed me at first but it soon became accepted to the point I did not even think about it. Editing sounds is definitely better with the use of the software editor. Apart from this the Tetra is an ideal synth to add some analog sonic character to your digital arsenal.

Leave a Comment

Please note: Comment moderation is enabled and may delay your comment. There is no need to resubmit your comment.