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Design Labs Prologue and Prologue Plus

Design Laboratories is a one-man company within a company (the Synthesiser Service Centre) and offers just four products within its range. The first, launched in 1992, was a RAM cartridge that offered the equivalent of four Roland M-64Cs in a single package and cost little more than one of the originals. The DX version arrived a year later, and this offered a similar price advantage over the Yamaha cartridge. The same year also saw the preview of a far more exciting product: an eight-channel MIDI/CV converter that incorporated a 24dB/oct filter for processing audio signals. The projected price was just £299, and delivery was expected in mid-1994. It's now mid-1995, and the production models, the Prologue and Prologue Plus, have just appeared. During the wait the original specification was re-written, two models replaced the original idea, the hardware was modified, and the software was enhanced… So was it worth the extra year's development?

The Prologue

The Prologue packs a lot into its small case. The back panel is busy with no fewer than sixteen 3.5mm CVs and Gates, plus sockets for MIDI In, Out and Thru. There are also two ¼" jack sockets that provide audio IN and OUT for the Retro-Synth. Since the Prologue is not rack-mountable, the top panel features the minimalist controls. These are a numeric keypad, a decidedly retro LED display, and a schematic of the Retro-Synth menus. You control the unit using the keypad, four keys of which emulate cursor keys, and the LEDs display the parameter names and values. It's far from ideal, but it is cost-effective. The cursors take you through four master menus (five on the Plus) and the options contained within each control every aspect of the units' operations.

The Prologue has four MIDI to CV processors, each of which can handle four notes simultaneously. The first menu, General Control, allows you to assign to each processor a MIDI channel, one of five keying modes, LFO, clock and portamento rates, four MIDI controllers, and pitch-bend amount. The processors can be treated individually or stacked to give 8-note and 16-note polyphony, although you'll need a second Prologue if you want to play 16 notes simultaneously.

Moving on, the Gate Output Table allows you to assign any of eleven gate-type signals derived from each of the four processors to any of the eight output gate sockets. Similarly, 24 continuous-voltage signals can be assigned from any of the processors to any of the eight CV outputs. The pitch control CVs can adopt the linear Hz/V standard as sometimes used by Korg and Yamaha, or the logarithmic V/Oct standard favoured by Moog, ARP, Sequential and Roland, and each may be scaled or offset as required.

In use, the flexibility offered by eight pairs of CVs and Gates is staggering. The gates offer just two states, 0V and 5V, but each of the eight CV outputs is a source of continuous voltage, and the range of mapping options means that each of these can carry a pitch CV or any one of hundreds of controller CVs. This means that, in addition to driving up to eight monosynths with basic pitch and gate information, you can play a synth such as an Oberheim 4-voice or 8-voice with four note polyphony and four continuous filter/amplitude/PWM (etc.) controllers. You can also use spare CVs to add vibrato, tremolo, filter LFOs, or other modulators to patchable synths. Indeed, just two CVs will free up oscillator 3 on your Minimoog, and three will turn an ARP2600 with a monophonic 3604 keyboard into one with a duophonic 3620 with LFO.

If there is a problem, it's that the Prologue's trigger and gate pulses are only 5V. This will drive most analogue synths, but there are some insensitive beasties that require more. Of course, you can route a Gate to a CV output that you've set up to offer a higher voltage, but you then lose that CV for other duties.

The Wasp Buzz option

Some pre-MIDI synths refuse to talk to conventional CVs and Gates. Examples of these include the EDP Gnat and Wasp. The Prologue's optional Wasp Buzz Interface will control these - albeit to the limited extent that those instruments understand external controllers. Its 7-pin DIN socket is located on the side of the Prologue and, while there are situations where the side-mounting may cause problems, the back panel is already full.

Operation couldn't be simpler: the output derived from Register #1 of Processor #1 is always available at the Wasp Buzz output, so you just plug a suitable cable between the Prologue and the synthesiser. Simultaneously, you can direct the note information used to drive the Wasp/Gnat to a conventional CV & Gate, stacking the EDP with a conventional synth for some really fat or layered sounds.

MIDI Facilities

The Prologue features a simple MIDI analyser that displays the last six bytes received, but its channel filter and re-channeliser is far more interesting. This allows you to select a single MIDI channel and filter the other 15 from any data stream presented to the MIDI IN. The selected channel can then be re-transmitted on any desired channel. The Prologue is, therefore, a solution to the OMNI ON and MIDI Channel 1 limitations of early MIDI synths such as the Roland JX-3P and Prophet 600. Sure, Anatek offered a MIDI Filter that ended up being sold off for less than £30, but it had no power supply and had to be re-configured every time you turned your synths on. I've got a Prophet 600 and an Anatek. Give me the Prologue every time.

The Prologue Plus with Retro-Synth

The idea behind the Retro-Synth is becoming quite common: take the signal produced by a relatively sterile source and imbue it with some of the qualities and warmth of a good analogue synthesiser. You achieve this by passing the sound through an analogue filter which, for best results, will offer envelopes that can be triggered and dynamically controlled using CVs or MIDI data. Dedicated filter banks from Analogue Systems and Peavey accomplish some of this, as do a number of analogue synths with audio inputs, but probably the best example is the Prologue Plus's Retro-Synth.

Retro-Synth is a '70s monophonic synthesiser with a multi-mode resonant 24dB/Oct analogue filter, two envelopes, but no oscillators. The dedicated ADSRs (one for the VCA and the other for the VCF) may be triggered over MIDI but, unlike most monosynths, the VCF, VCA, and envelopes are also sensitive to velocity and aftertouch.

Using Retro-Synth couldn't be more intuitive. The Plus's fifth master menu selects five sub-menus that replace the knobs and switches of a true '70s instrument. Menus 1 and 4 are the VCF- and VCA- envelopes. Menu 2 adjusts the filter's initial frequency, resonance, ADSR amount and keyboard tracking. Menu 5 controls the VCA level, velocity and aftertouch responses; and Menu 3 gives access to the filter mode selector, and the filter's velocity and aftertouch responses. Hold on a sec... filter modes? There are 14 of these, offering low-pass, high-pass, notch and band-pass filters, each offering a range of Qs and roll-offs. Some include equalisation, some do not. All are fully resonant.

So how does it sound? To find out, simply connect the audio Out from your sound source to the Retro-Synth In, the MIDI Out to MIDI In, set the parameters, and play. The Retro-Synth envelopes are triggered each time a Note On is received, and all the velocity and after-touch information is interpreted and directed to the appropriate parameters. The result is similar, but superior, to that obtained when you play other polyphonic but single-filter synths such as the Polymoog, ARP Quadra and Korg Poly800. And it's magic. Taking the one of the most soulless synth in existence, I created resonant voices, punchy lead and bass patches... and the flexibility of the envelopes (10ms to 10s) and the almost ridiculous range of resonant filter effects will keep even the most demanding knob-twiddler happy for a long, long time.


At around £300, the Prologue demands attention. It has 16 assignable CVs and Gates. It will filter and re-channelise MIDI data. It features 24ppqn DIN Sync, which shares the MIDI Out and drives fashionable items such as the TR808 and TR909. It has a dedicated interface for the Wasp and Gnat synthesisers. Let's face it... it's excellent value for money. Another £120 also buys the Prologue Plus with its Retro-Synth which is, in this enthusiast's opinion, a must-have. There are, of course, compromises, and the Prologues' low costs are clearly reflected in The Design Laboratories' choice of hardware. The software also shows a number of short-cuts, though deficiencies such as the lack of configuration memories and SysEx could be rectified in a software update. Provided that The Design Laboratories achieve the right compromises between low cost, build quality, and reliability, the features of the Prologue and Prologue Plus make them winners.

Download the Prologue and Prologue Plus manual here.

Copyright ©1995, Gordon Reid.

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