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Octave-plateau Voyetra Eight

Programmable 8-voice Synthesizer

From the seventh floor of a New York building, Octave-plateau Electronics Inc have conceived the Voyetra series as the 'next step in the evolution of electronic portable keyboards'. The basic idea is simply that the synthesizer comes as two separate units — a keyboard controller and a rackmounted package that generates your sounds. That's not really something new, as EMS, ARP, Korg and Roland have all produced systems with separate keyboards in the past.

Nevertheless, the Voyetra Eight does have one very big advantage over these earlier machines in that it is designed to be non-obsolescent. The sound generating system comes in a very strong, portable 19" rack-mounting case and contains a micro computer that controls eight synthesizer circuits, all on removable cards closely stacked vertically inside. This allows upgrading of the system as OEI introduce new circuits, controllers for other instruments such as guitar and home computer links. The current keyboard controller, the VPK-5 is cleverly connected to the Voyetra module by a standard microphone cable (up to 20ft long) that lets you get on with the playing and still control the whole range of different programmable effects in performance from its four-way joystick and velocity and pressure-sensitive keys.

The other important feature of the Voyetra Eight module is that you get much more than what you see. The front control panel consists of 42 switch buttons (including numerical keypad) and 18 small pear-shaped rotary control knobs, many of which have multi-functions accessed in complete panel groups called 'Pages'. Three large pairs of red LED alpha-numerical displays and numerous red LEDs serve as indicators to Pages and functions in use, for complete editing and complex programming of sounds, arpeggiation, as well as real time polyphonic sequencing.

Surprisingly, the synthesizer VCOs, VCFs and VCAs are all analogue, although the reason for this is to keep the sound quality free from digital quantisation effects. The rest of the module is digital, including the ADSRs, LFOs and Sample & Hold, and the built-in micro has almost total control of the calibrated monitoring of the instrument, enabling storage of 100 sound programs. In addition, a 100-stage program 'Stepper' allows panel settings to be stored and recalled in any order with virtually all the performance parameters you require for each sound. These and other functions can also be dumped onto standard cassette tape.

Internal circuitry of Voyetra module.


The Voyetra Eight module is of sturdy construction employing 3 mm fixing plates for a 19" rack, being quite heavy at 16.8 kg, and measuring 483W x 133H x 305D mm. It has open grilled top and sides for ventilation since it dissipates a fair amount of heat from its tightly packed boards. Each PCB card fits onto a motherboard across the base and can be removed for servicing. All sockets are standard jack except for the remote keyboard and MIDI sockets which are XLR types. The latter posed a small problem since it's the only MIDI instrument we've used without 5-pin DIN sockets! But they obviously keep the professional quality in terms of on-the-road usage. Actually, the review model had no MIDI interface built in — this presumably plugs into the multiway socket at the rear.

The case is finished in light grey with black/grey plastic/mylar front panel and windows for the large ¾" LED displays. Switches are all small micro types, colour-coded blue, white, grey or red. A stereo headphone monitor socket is provided and the main on/off switches are also brought to the front.


The VPK-5 keyboard is very well made, with strong light metal case and hardwood end pieces. The 4-direction joystick is finished in chrome with 'left', 'right' selected assignment buttons (according to the Page you are using) situated above. A pressure sensitivity pot control is an unusual but useful extra (no — we haven't lost its control knob!).

The key action is quite firm and springy and did make the velocity sensitivity to be a little variable for dynamic control. Velocity can also programmed for various modulation effects and different keyboard 'tapers'. Pressure control can be varied to be immediately on with each key depression up to requiring hard key pressure. The joystick is a spring-loaded return-to-centre type, with left/right directions programmable for specific modulation effects (through what is called the Poly-Mod Bank System) and forward/backward pitch bend up or down a fifth.


There are two stages in Programming. First, you shape your sound using internal 'Edit Pages' and then store it in a Left Program memory or Right Program memory — holding up to 100 different programs in all if required. (In other words, Left and Right Program memories may hold the same sound or any dual combination of 100 memories).

Second, you use the 'Stepper' (termed a 'Program Programmer' by OEI) which allows you to set and memorise 100 combinations of the following controls:

Program No, Octave, Volume, left/right Keyboard Modes
All Trimmer settings
Arpeggiator settings, left/right including speed etc
Pitchbend and pressure defeats, left/right LFO1 and 2 sync
Velocity controlled Volume, left/right

A most useful feature is that the Step programs can call up programs in any order, although in performance you'll be stepping through these 100 locations forward or backward (using the two keyboard switches or optional footswitches). Step memories can also be saved on cassette. An added bonus that provides on-board capacity for 300 sounds comes when you edit a Program and store this within a step. From a studio point of view, an external clock can be used and, in conjunction with a click track on your multitrack recorder, will allow complex layering of sound in sync.

Left hand side of control panel.


Each of the Voyetra's eight voices has two VCOs and a white noise generator that feed into a 4-pole, 24dB/oct low pass VCF and then into the VCA. Both VCF and VCA each have their own ADSRs and VCO1 may bypass the VCF to get a wider range of timbres.

Both VCOs have four waveforms that can be added together: sawtooth, triangle, variable width pulse, and sub-octave square. The VCOs can be synchronized for dramatic harmonic effects and independent volume controls are provided for each enabling audio outputs to be switched right off when using a VCO as a modulation source. Ring modulation effects are easily obtained by sending the summed waveform output of VCO2 to the linear FM input of VCO1.

VCO keyboard tracking can be switched off to use it as a polyphonic LFO and both VCO pulsewidths may be modulated by either of the two LFOs and ADSRs. As modulation depth is variable, it's possible to make modulation increase with keyboard pitch. No combination of routing seem to have been left out and both VCOs can be independently modulated from all four Poly-Mod banks.

Further refinements of control let the ADSR 'decay' and 'release' track the keyboard to give shorter times on higher keys, similar to acoustic piano and other traditional instruments. Key velocity can also control the attack rates. Unconditional and Normal modes for ADSR triggering give control of individual note decay and sustain can be switched out to give percussive ADR envelopes. Release times can also be switched out using panel or footswitch 'defeat'.

There are two LFOs, each having sine, sawtooth, triangle and sample and hold outputs that can be sent as modulation sources for all four Poly-Mod banks. LFO outputs can control VCO pulse widths and arpeggiator (Left Program) speed. LFO 1 has a variable delay and an additional square modulation output. Both waveform 'starts' from the keyboard can be sync'd, as well as left and right LFOs in Split Keyboard mode.

Poly-Mod Banks

Very comprehensive modulation is made possible on the Voyetra by the Poly-Mod banks, as they are called. The first important point to grasp with them is that its 8 modulation 'sources' are monophonic or polyphonic. 'Mono' sources are applied to all eight voices simultaneously and are DC (for bending and sweeping effects), LFO1, LFO2 and LFO1 square. 'Polyphonic' sources are ones generated individually for each of the eight voices in the system, and include VCO1 and VCO2 summed wave outputs, ADSR1 and ADSR2. Any source can be inverted for reversed sweeps and so on.

Each of the Poly-Mod banks 'sources' go to a 'controller' and then to any combination of 'destinations': VCO1 & 2 pitch control, VCF Cutoff and VCF Resonance. Mod depth can be set numerically from 0 to 255.

Performance Power

The real strength of all those modulation possibilities lies in the 'controllers': key velocity, key note control voltage, key pressure, joystick control, programmable foot pedal, ADSR1 and low frequency noise. Four distinctive modulation control situations can be created — not just a single complex one! With the Voyetra module's storage capability, you can call up the most spectacular mod arrangements in performance using the keyboard and a number of footpedals. You'll not be short on output volume either, as the Voyetra puts out a massive signal up to 20V!

Right hand side of control panel.

Panel Pages

With Octave-plateau's claim that the front panel would need to be 17ft long to provide a separate control for every function, it's no wonder that they devised the Paged Panel concept. Ten pages are currently available and more are likely to be provided in the future. The only snag with this arrangement is that the front panel legends only refer to the first 'Normal' page functions, so you have to keep checking the panel schematics for each page in the comprehensive instruction manual. But with continued use you certainly pick up the individual page controls as you go along.

Normal Page

This is the power-up page with functions as labelled and incorporates most performance controls for calling up programs and varying main parameters and arpeggiator settings using the buttons and rotary controls. The latter do not necessarily indicate the actual setting until individually operated to make an instant change to a parameter. Normally these temporary changes are lost once a new program (a sound 'patch') is called up on the LED displays in the Programmer section. Although the small pear shaped knobs feels rather inadequate, there appears to be plenty of control available - for example, Release and Decay times extend to more than 1 min 45 sec.

Alternate Page

Entering this and the other pages is by means of 'hidden' functions. For this page for example, you press 'A440' and 'Step Enable' buttons together. This page transfers programs within the Voyetra's memory banks. (A rear panel memory protect switch is provided and memory is stored on switch off by battery back-up). It's not just a swapping process, as you are able to edit a sound (jumping to other pages to do so if necessary), store it in a new location, and leave the original intact.

Other functions control the Arpeggiator, as well as VCA velocity, key pressure and VCO1 detune 'defeat' (left and right programs).

The Arpeggiator has the accepted Up, Down, Up and Down and Random effects. More interesting is that speed can be remembered in a program 'Step' and left and right programs can have different arpeggio speeds, plus keyboard retriggering of both clocks — and even auto octave shift! External clock in and out is available too.

The VCF is unusual in that not only can the Frequency Cutoff be modulated by the ADSR and Poly-Mod banks, but also the Resonance (Q) control. In effect, the latter will allow sweeping changes of harmonic emphasis to the point of self-oscillation — some pretty original stuff can be made in this way. Keyboard tracking of the filter is also variable.

ADSR1 goes to the VCF and ADSR2 controls the VCA — this VCA also receives velocity sensitivity voltages for playing loud and soft on the keyboard. Both ADSRs can be assigned to the four Poly Mod banks.

Velocity Taper Page

The 14 Program Parameter trimmers let you tailor the velocity control in a variety of ways. By striking a key yourself in this mode, a value of 0 to F (hexadecimal scale) will indicate the strength (or velocity) of your 'strike'. This can then be a guide for setting the trimmers (assigned 0, 1, 2 to A, B, C, D, E) so that a strike of 'A' intensity with trimmer A turned fully on will give full modulation of whatever you're controlling — dynamics, vibrato and so on. In this way, loud and soft playing can be reversed, or vibrato (or some other modulation) can be made to come on at only the loudest strikes.

This is an unusual facility and requires you to pre-plan all your programs carefully — if you don't write it down you're bound to forget what you set for one of your 100 program steps!

Poly Sequencer Page

This page will have a lot of appeal to real time players (as opposed to 'enter by music' musos). Rather than provide the individual 'tracks' to build up your piece, you can record sequences (poly or mono) on top of sequences onto two separate channels (rather like doing sound-on-sound taping).

Once again, it is worth considering carefully whether the poly sequencer offers enough note storage for the kind of music you compose. For example, the two channels allow two separate sequences of 850 'events' but that actually means 425 notes each. It's also possible to record up to 1700 events (850 notes) in one Record sequence and footswitch control of start/stop is provided. The displays show the number of events left and on playback you can still play the keyboard along with your recorded sequence.

The sequencer will operate in the various keyboard modes available. These are Whole 8 mode, playing Program Right sounds; Split Mode, playing Program Left and Program Right sounds on opposite sides of the split point (normally split two octaves/three octaves over the five octave C to C keyboard, but redefinable in performance). Unfortunately the split point is not programmable and will default as just stated. Only four notes are available on each side of the split. Similarly, in the next Layer mode four notes each have two voices — giving the most variety of sound. Despite the limitations of four notes, I preferred to use this mode most of the time.

Unison mode is another very useful assignment because it can be used in Split as a powerful four voice mono lead with a chord accompaniment. With Layer and Whole 8 you get 4 or 8 voices per note for thick cutting lead lines.

Glide (Portamento) and chromatic Glissando can also be used between notes and chords.

Back to the Sequencer! While you're playing away your sequence, you can be editing the sound and changing programs to vary the timbre, and looping is also possible, but relies on accurate use of the 'stop' switch at the end of the sequence — rather hit and miss in practice. Playback speed can be doubled, halved (from the keyboard buttons above the joystick if you want) or continuously varied.

Some very useful control routines are implemented: Auto goes straight into play after record: Overdubbing — bouncing from Channel 1 to 2 and back until the memory is full; Continuous Overdubbing — does all the switch over of both channels from record to play automatically: Auto-Continuous Over-dubbing — will keep going through the overdubbing process while you get on with the playing; Stevenson Mode — this is perhaps the most powerful function as it lets you record a passage, play it back, record another passage, playback, and so on, all from one footswitch.

Sequences can then be stored on cassette tape using Load and Dump functions.

Edit Pages

There are six Edit Pages which you can cycle through using forward/reverse switches on the module or keyboard. Here you can create your Program sound patch by setting VCO tuning, volume, waveforms, VCF and ADSR parameters, and Poly-Mod banks A, B, C and D. The latter have slight differences in order to accommodate extra modulation controllers.

Editing and Expansion

Quick editing is provided by the Normal page, including one octave up or down for left or right programs. A Master Tune control sets overall pitch and, besides the internal edit pages, it's possible to go into external edit through the MIDI to display and edit programs and probably do more extended sequencing. OEI intend to provide soft and hard interfaces for Apple II, IBM PC and Commodore 64 (what — no BBC B or Spectrum?).

Tape storage can be for programs, steps, user tapers for velocity, and sequencer notes. Individual programs can be dumped too. Tape Dump takes 1 min 20 secs and disables the keyboard.

And if you're worried about tuning you just press the Auto Tune button, which goes through a visual diagnostic check as well.

There's also an Auto Mute button for cancelling main audio output while you monitor on headphones.

Rear connection panel.

Rear Panel

This final audio output is sent to stereo left or right, and mono output sockets, the latter being a mix of left/right programs. In Whole 8 mode, voices are panned across the stereo field — set by means of a row of presets inside the Voyetra Module.

There are footpedal inputs for Pitch Bend, Volume and Filter sweep. Stereo footswitch inputs for Program forward/reverse, release defeat, hold, glide, arpeggiator pause, and there's an expansion socket for another Voyetra Module to be controlled from the same keyboard for 16 voice operation. There's also CV and Gate left and right outputs to drive two slave mono synths (1V/oct types), plus sockets for cassette interface and arpeggiator clock.

Voyetra Eight.


There's no doubt that this is a very desirable instrument by virtue of its extensive synthesizing capabilities. The sounds are still very much 'analogue' and retain the traditional warm, fat and punchy qualities we've come to expect from the analogue synths. Background noise is very low and the instrument is ideal for studio recording. The MIDI interface and software for Apple II is now available (an IBM version will arrive in late October), and is claimed to work on all other MIDI instruments!

The system is professionally built from beginning to end — but it is in the expensive class at £3,750 including VAT. If that doesn't deter you, then you'll enjoy an instrument that is very playable and highly orientated towards sophisticated performances.

The Voyetra Eight is available from Computer Music Studios, (Contact Details).

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Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Oct 1983

Review by Mike Beecher

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