Outside the Box
Physically, Tetra is similar to Mopho, with four assignable parameter controls per program and a row of controls dedicated to the most commonly used performance parameters. All of the parameters can be accessed from the front panel and Tetra is fully programmable. A free, downloadable editor is available for Mac OS and Windows to facilitate more comprehensive tweaking.
Most of the rotary controls are detented encoders, but Cutoff and Resonance are potentiometers, allowing full sweeps with a single turn. The Push It button is a manual trigger to play notes and latch sequences on without the need for a MIDI controller.
Audio is output in mono, stereo, or per voice, via the four audio output jacks. There is also a headphone out. MIDI communication is by standard MIDI in and out jacks or USB. Poly Chain Out is a special, dedicated MIDI output to chain multiple instruments for increased polyphony.
Under the Hood
The voice architecture is based on the Prophet ’08, but with the addition of a sub-octave generator for each oscillator and a fully programmable feedback loop for each voice. That breaks down to two DCOs, a resonant low-pass filter, three DADSR envelope generators, four LFOS, deep modulation routing, an arpeggiator, and a 16 x 4 analog-style step sequencer per voice. Feedback is capable of producing effects ranging from mild distortion to fairly extreme harmonic instability. (That’s a good thing.) The possibilities are nearly endless. And the audio signal path is 100% analog.
Tetra a la Mode
In Program Mode, Tetra is a four-voice, polyphonic synthesizer with four banks of 128 programs. As with the Prophet ’08, each program contains two layers—each layer is essentially a separate patch—that can be used to create keyboard splits or stacked sounds. Banks 1 and 2 are the Prophet ’08 factory programs; banks 3 and 4 are a combination of Mopho and new programs.
In Combo Mode, a different program can be assigned to each of the four voices. Combos can be used for mammoth unison patches or for triggering up to four different 16 x 4 sequences—each with its own program—simultaneously. Combos can also be used to create “modular-style” polyphonic patches, where each voice plays a different program, with a slight variation on the same sound or even a drastically different sound.
In Multi Mode, Tetra becomes a multitimbral sound module capable of playing four monophonic parts on four MIDI channels, with separate outputs for each voice. Coupled with a MIDI sequencer and DAW, Tetra can play complex arrangements or analog drum parts with each part individually processed and recorded to its own track.
This One Goes to 12…and 16
Up to four Tetras can be poly chained for eight, twelve, or sixteen voices total. When used with a Prophet ’08, up to two Tetras can be poly chained for a maximum of sixteen voices. In addition, the Prophet’s front panel controls map directly to almost all of Tetra’s parameters, so the Prophet acts as a programmer and control surface. And a Mopho can be connected to Tetra’s Poly Chain Out for five-voice operation.