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Waldorf Microwave

The PPG Wave was one of the most powerful synths of the early Eighties, but it died a death along with so many other dinosaurs. Now its particular method of wavetable synthesis lives again in an entirely new rack expander, which combines the best of the Wave's original audio architecture with full MIDI control. Paul Ireson learns how to cook better sounds, faster.

When one is surrounded by equipment that sometimes becomes obsolete before you've saved sufficient money to buy it, it is reassuring to see tangible evidence that certain synthesizers have a value and quality that extends their useful life to positively methuselan proportions. The availability of MIDI retrofits, MIDI-to-CV convertors, and off-the-shelf MIDIMoogs and Obie Racks is testimony to this fact, and people aren't shelling out hard cash for nostalgia - the best of these analogue classics offer enormous sound quality and potential, in an easily accessible form, and that will never go out of fashion.

The Waldorf Microwave is another product that is in some sense reviving a classic instrument, but with an important difference - if the MIDIMoog is an instrument finding a product afterlife with the aid of some new voodoo electronics, the Waldorf Microwave is a clear case of reincarnation. The unit is a completely new set of production electronics, based on the circuitry of the original PPG Wave 2.3, squeezed into a 2U rackmount case. Now, for those who don't remember the PPG, it was one of the big instruments of a few years back - big in both the size and reputation stakes - and it came with a hefty price tag of around £5000 to match. The PPG Wave 2.3 and its predecessor, the Wave 2.2, offered a unique digital/analogue hybrid sound, a result of processing oscillators that played digital waveforms from complex 'wavetables' through analogue electronics, and it was generally regarded as an instrument of outstanding versatility and sound quality. The main reason that you won't find many PPGs in studios these days is that even the later versions with MIDI proved to be extremely sluggish in responding to incoming note data.

Designing new audio circuitry, more or less from scratch, gives the Microwave a clear advantage over its previous incarnation in that MIDI is incorporated in the voice and modulation architecture at the most fundamental level, and also that the instrument can be produced a good deal more cheaply - at £999, the Microwave costs roughly a fifth of what you'd have paid for a PPG Wave 2.3.


I think I'd admit to having a soft spot for any device these days that forgoes an abstract alphanumeric code for a real name. Purely by way of comparison, I tried cranking this Microwave up to full power - 650 Watts - for five minutes, and believe me, it cooks. It's about a thousand times more satisfying than a TV dinner, and it annoys the hell out of the neighbours!

The unit has an unconventional appearance - a blue front panel, a bright red alpha dial, a red OK/Cursor Locate button, and several silver Mode/Edit Page selector buttons. This particular styling seems to me to walk a fine line between Fisher-Price ghastliness and offbeat cool, and frankly I can't decide which side it's about to fall on - but at least it's different.

To get down to the all-important sound of the Microwave, it is essentially an 8-voice, two oscillators per voice synth with 4-pole lowpass analogue filter, two LFOs per voice, and three envelopes per voice. Although the later stages of the voice architecture are conventionally analogue, the oscillators use complex digital wavetables as their sources, and each wavetable contains a set of sampled waveforms with progressively changing timbral characteristics. By sweeping through a wavetable, each oscillator can generate a sound that has enormous movement and depth, even before further sound-shaping tools are brought into play - this is the basis of what Waldorf describe as Dynamic Spectral Wavetable Synthesis. Extensive modulation is possible at almost every stage of the voice architecture, using the envelopes, LFOs and almost any MIDI source you care to think of.

The analogue side of the Microwave enables it to produce fat bass and lush synth string sounds with ease, but it's the wavetable synthesis that makes it special. The effect of sweeping through a wavetable can be like adding a whole new dimension to a sound - it can be subtle, or totally gut-wrenching, and it needs to be used with care to avoid generating too many over-the-top and unusable sounds. The choice of waveforms in the wavetables gives the Microwave access to a wide range of metallic, bell-like, and just plain unearthly textures that would otherwise be out of the reach of analogue electronics. The only other contemporary instrument that employs this kind of synthesis is the Ensoniq VFX (which I feel is still the most exciting synthesizer available at present), but the differences between the two are more significant than the similarities - not least in that one is primarily a performance keyboard, and the other is a rack expander.

The sounds of the Microwave can be played in one of two play modes - Single and Multi. In Single mode, you can play any of the 64 Single patches, which are arranged in two banks of 32. A further 64 Single patches can be stored on optional ROM or RAM cards. In Multi mode you can play any of the 64 Multi patches, each of which combines eight Single patches into one, enabling such set-ups as multitimbral combinations for use with a sequencer, or performance arrangements using keyboard splits and velocity switching. Again, a further 64 Multi patches can be stored on ROM or RAM cards. All sound locations are fully user-programmable - there are no immutable factory presets.


The preset factory sounds of the Microwave are a very mixed bunch, and certainly don't give the good first impression of the unit that they really should. A handful are excellent, displaying the full potential of wavetable synthesis, but the rest are either weak and dull or go too far down the road of 'cartoon sound effect' gimmickry. Improving on many of the presets was a matter of a few simple tweaks, but it was when I commenced programming my own sounds that I really began to appreciate the Microwave's power. Perhaps the lack of good presets is a blessing in disguise, because it will force users to programme their own original, personal sounds, and it is here that the Microwave excels.

The Single sounds are based on two oscillators. Oscillator 1 can select any one of 32 wavetables as its source of waveform(s), and Oscillator 2 must also use waves from the same table. Each oscillator can be tuned over a range of two octaves up or down, with semitone and fine resolution, and the bend range for each set independently.

Two sources of modulation can be applied simultaneously to the pitch of each oscillator. It's worth explaining how these work in a little detail now, as the same system of two modulators is used throughout the voice architecture. Modulator 1 is the more flexible of the two, using a sidechain modulation system whereby the level of the Modulation Source is in turn modulated by a Modulation Controller. Both the source and controller can be any one of the following: LFO1; LFO2; Volume Envelope; Filter Envelope; Wave Envelope; LFO Envelope; Key Track; Velocity; Release Velocity; Aftertouch (monophonic pressure); Poly Pressure; Pitch Bend; Mod Wheel; Sustain Pedal; MIDI Volume; MIDI Pan; Breath Controller; Controller W-Z; Max; Min. Controllers W to Z are assignable MIDI controllers. You can also set an overall modulation amount for Modulator 1.

Modulator 2 is simpler - you can only set a source and amount, although it does have an additional quantisation parameter which allows you to 'coarsen' the resolution of the modulation data. If you've just programmed a whole set of modulation parameters for Oscillator 1, and can't be bothered to repeat the process for Oscillator 2, a Link Mod function allows the modulation parameters for Oscillator 1 to determine the modulation routing for both.


The waveforms played by each oscillator must be derived from the wavetable specified for Oscillator 1 in the 'Wave 1' edit pages. There are 32 wavetables, each of which contains 61 related waveforms, along with triangle, sawtooth and square waves. An oscillator can select a single waveform to play, or sweep through all or part of the table as a note progresses. In the former case, you could imagine the Microwave as being similar to a conventional analogue synth, only with over 1800 different basic waves to choose from; though, of course, it is the ability to sweep through a wavetable that makes the Microwave exciting. The supplied wavetables allow for the creation of some excellent sync sweep effects and metallic tones, as well as for much more acoustic textures.

Having selected a wavetable, you can then specify a Start Wave point for each oscillator. If no modulation is applied to the playback point, this will determine which of the 61 waveforms is played - if modulation is used, then it determines the point around which the playback point will be modulated. You can also set a Start Sample (0-127). This selects at which sample within each waveform playback begins - the point of this being that if the two oscillators are playing very similar waveforms and are not detuned from one another, then shifting the relative Start Samples for the two waves will affect their phase relationship, and will therefore create notches in the audio spectrum which may be quite noticeable.

Several sources can be used to modulate the wave playback point simultaneously: the Wave Envelope; Keytracking, Modulator 1; Modulator 2. A single Wave Envelope is used for both waves in a voice. The effect of the envelope can be positive or negative, and can be scaled up or down by velocity. Modulator 1 and 2 operate as described for pitch modulation. You can specify whether the wave modulation will be Smooth or Stepped, which determines how smooth the sound of an oscillator is when the Start Wave point is shifted relatively fast. On the Stepped setting, the movement between waveforms may be much more noticeable, and the overall sound a lot 'dirtier' as a result - whilst for some sounds this will inevitably be a bad thing, for others it gives the Microwave's sound a powerful, gritty character that is a welcome change from delicate, atmospheric digital textures. As with the pitch modulation of Oscillators 1 and 2, you can link Wave 2's modulation parameters to those of Wave 1. However, this ease of programming is generally bought at the price of a rather more static sound.

Any instrument that employs sampled waveforms as the basis of its sound can either be a closed system, and restrict you to one set of raw material, or open ended, and allow further waves to be added. The Microwave falls into the latter category - although I wasn't able to test this aspect of the unit, it should be possible to load a further 12 wavetables via a MIDI System Exclusive dump, and 12 from a plug-in ROM card. Third party developers are apparently working on new wavetables right now.

Next in the audio chain comes a simple mixer, where the two Waves are mixed with white noise before being passed through to the filter stage. The levels of each Wave and the noise source are variable from 0-7, and a total level of more than 8 can result in distortion, depending on the waveforms chosen. This enables some excellent distorted/overdriven sounds to be created. An overall mix level can also be set, to scale the output of the three mixed sources to a suitable level, and this is modulated by a dedicated Volume Envelope, Keytracking, and two further modulation sources as already described. MIDI Volume (Controller number 7) is permanently assigned to control volume, sensibly enough.


The filter section of the Microwave is nothing short of superb - a classic (sorry, there's no other word for it) 4-pole lowpass analogue filter with a 24dB per octave rolloff. Resonance is variable from 0-127, and around 80 the filter goes into self-oscillation. Filter Cutoff can be modulated by the Filter Envelope, and two additional modulation sources as previously described. In addition, the Resonance value can be modulated by any one of the standard sources. A filter like this really is a very powerful sound-shaping tool - it can be rather unsubtle, but it sounds very smooth, and the ability to control resonance up to and beyond the point of self-oscillation makes it extremely creative.


The three envelopes - Wave, Volume and Filter - are the principal means of shaping the Microwave's sound, and they are hardwired to their respective principal destinations as well as being available to modulate other aspects of the sound wherever a modulation source can be selected.

The Volume Envelope is the simplest, being a straightforward ADSR type. You can set modulation sources and amounts independently for each stage of the envelope. The Filter Envelope is identical, apart from the addition of a Delay parameter (and parameters controlling its modulation), which allows the onset of the filter envelope to be delayed by up to 36 seconds.

The Wave Envelope is quite different - it is an eight-stage envelope, with a Time and a Level set for each stage. Time and Level Modulation Source and Amount parameters allow the envelope times and levels to be universally modulated. A Key Off Point parameter specifies at which point the envelope's sustain stage is inserted, and a loop function allows you to set the Wave Envelope to repeatedly loop a section from any one stage to the end, which can create some interesting rhythmic effects quite distinct from any LFO modulation.


It would be a shame, given the range of excellent sounds that the Microwave can produce, to restrict yourself to only playing one sound at a time. Fortunately, Multi mode gives you access to up to eight sounds at once. Eight Single patches can be used in each of the Multi patches, and 64 Multi patches can be stored in the Microwave's memory. The arrangement is very simple - each Multi patch has eight parts, and you simply assign a MIDI channel and Single patch to each. You can also transpose and alter the volume of parts, and set note and velocity ranges within which they will respond, enabling keyboard splits and velocity-switched sounds to be created by assigning more than one part to the same MIDI channel.

Voice allocation between the parts is dynamic, which saves you having to decide where to use voices, but with only eight voices on hand, it can be very easy to run out of polyphony. As a result, the Microwave is not the kind of expander that will churn out several complex chordal parts at once, and is therefore not suitable as the main expander for a MIDI studio - a D110 or an M3R would be a better choice here - but it will deliver one or two excellent sounds in a mix, that will stand quite apart from everything else.

Each part can be allocated to one of the Microwave's four separate audio outputs, as an alternative to the stereo outs. The separate outputs are monophonic only, so although they are fine for isolating monophonic sounds (eg. for a bassline), they're unsuitable for outputting chordal parts.


In the name of user-friendliness, the Microwave provides facilities to speed up sound programming. Firstly, there is a set of Fast Access editing pages, which allow you to edit several parameters at once. So, for example, the Envelope Fast Access page contains four rather special 'parameters': Attack, Decay, Sustain and Release. Modifying any of these Fast Access 'parameters' will affect the relevant portions of all three envelopes in a patch, thereby providing a rapid means of controlling the broad time-variant characteristics of a sound. There is also an Envelope Amount Fast Access page, in which you can adjust the amount by which each envelope modulates its principal destination, and a Velocity Fast Access page, in which you can globally adjust the amount of velocity modulation routed to all envelopes, and as a Modulation Source, and as a Modulation Controller wherever it is assigned. Similarly, the Aftertouch and Mod Wheel Fast Access pages, respectively, allow you to universally alter the amount of Aftertouch or Mod Wheel modulation applied as a Modulation Source and as a Controller.

A second means of easing the programmer's burden is provided by the Macro function. This simply allows you to impose one of several sets of preset (non user-programmable) values on a particular group of sound parameters, to achieve a certain character in one aspect of the sound. Envelope Macros impose preset shapes on any of the envelopes, and the Modulation Macros create certain kinds of modulation effects. These basic envelope shapes or modulation effects then provide the starting point for your own programming.


There are certainly more details about the Microwave that I could delve into, but I think it's more important to get across the broad point that this is an extremely powerful and useful synthesizer, and one that is tremendously satisfying to use. Far from being merely a resurrected analogue classic, the Microwave is a well-designed, viable, and highly expressive contemporary MIDI sound module, with a unique sound. The only comparable instrument is the Ensoniq VFX, which in many ways is more versatile (partly through the provision of sampled sounds, built-in effects section, etc) and has the advantage in multitimbral operation of being up to 21-note polyphonic. But the Microwave scores in having more onboard wavetables plus the facility to add more still, a more powerful filter section, and a mixer section that can be deliberately overdriven - these last two features in particular contribute to a marked difference in the range of sounds that the two instruments can produce. A very significant difference is that whilst the VFX is a performance-oriented keyboard with stereo outputs, the Microwave is a rack expander with separate (albeit monophonic) outputs.

The Microwave sets itself apart from most of today's expanders in that, despite its name, it is not the hi-tech music equivalent of a ready meal - instant gratification and no real beef. The currently supplied presets fail to do it justice by a long shot, but once you've created a few of your own sounds you'll realise that this is an instrument with lasting appeal. Its method of sound creation is both comprehensible and versatile, and the sound is as capable of solidity and raw power as it is of encompassing delicate, ethereal textures. The modulation possibilities are a major factor in making the Microwave so exciting and so expressive - another feature that it could be said to share with the VFX.

Having just made that comparison, however, I have to finish by emphasising that in the final analysis the Waldorf Microwave is unique. Whereas most rack expanders seem to be striving to do everything - instruments, drums and effects - and therefore either fail to do anything particularly well or become partly redundant when another unit will do any single task better, the Microwave is the result of a clear intention to produce a modern classic. It could not be the main expander in a MIDI studio, but what it does - producing its distinctive, glorious sound - it does like nothing else available today.


£999 inc VAT.

The Bridge, (Contact Details).


  • 8-note polyphonic, 2 oscillator per voice synthesizer module
  • Dynamic Spectral Wavetable Synthesis
  • 4-pole, 24dB per octave lowpass analogue filter
  • 3 envelopes per voice (Wave, Filter, Volume)
  • 2 LFOs per voice
  • 32 internal ROM Wavetables
  • 12 Wavetables loaded via MIDI System Exclusive
  • 12 Wavetables on ROM card
  • 61 Waves per Wavetable, plus square, sawtooth, triangle
  • 12-bit sampled wave storage
  • 4 separate monophonic outputs
  • Stereo Left and Right outputs
  • 64 Internal Single sounds
  • 64 Card Single sounds
  • 64 Internal Multi sounds
  • 64 Card Multi sounds



Two of the Microwave's most important sources of modulation data are the two LFOs - LFO 1 is the more complex controller, and LFO 2 is a little simpler. You can set Rate (0-63), Shape (sin, triangle, pulse, random), Symmetry and Humanise parameters for both. Symmetry affects the precise shape that the triangle and pulse waves will take, varying the triangle wave from a positive to a negative ramp sawtooth, and pulse wave from a 5% to a 95% duty cycle. Humanise imposes a random variation on the LFO rate.

Whilst that is as far as LFO 2 goes, LFO 1 gives you several more parameters to play with: Rate Mod Source and Amount; Level Mod Source; Sync On/Off; Delay; Attack; Decay. Sync enables the LFO 1s for all voices to be synchronised, to recreate the sound of a single LFO poly-synth.


The Pan position of a sound in the stereo image is a further parameter that can be modulated in real time - you set a basic position (with a resolution of 128 steps, 0-127), and select a Modulation Source and Amount. With the Pan position of different notes being quite independent, some lovely spacious effects can be created with envelope or LFO modulation here.

The Microwave's Glide options allow for both portamento and glissando, and both can be operated in either a fixed glide time or fixed rate mode.

Also featuring gear in this article

Previous Article in this issue

Ian Boddy

Next article in this issue

Casio CSM-10P

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Dec 1989

Donated & scanned by: Mike Gorman

Gear in this article:

Synthesizer Module > Waldorf > Microwave

Gear Tags:

Digital Synth

Review by Paul Ireson

Previous article in this issue:

> Ian Boddy

Next article in this issue:

> Casio CSM-10P

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