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Casio CZ101

Programmable Phase Distortion Polysynth

At last, Casio come up with the pro keyboard goods. Paul Wiffen tests the first of a whole range of synth gear from the calculator people, and concludes that it's 'probably the best Casio of all time.'

Casio launch not only a new product aimed at a new market, but a new concept in sound synthesis - Phase Distortion. Can all this innovation really cost just £395?

Ever since the company's miniature VL-Tone took the electronic keyboard out of the specialist music shops and into the High Street chains of Dixons and Argos, the world and his wife have been waiting for Casio to produce a professional synth to turn that market on its head in a similar manner. Their first musical instruments - the CT201 and its successor, the 202 - were reasonable enough. For under £300, they gave the semi-pro keyboardist access to a variety of good-ish sounds, but both were short on - if not entirely lacking in - programmability. That was supposed to be rectified with the advent some little while later of the CT1000P, but for my money it retained too much of the 'preset' philosophy - certain waveforms only available at certain octaves, not much in the way of memory space, and so on.

After that disappointment, I was sceptical that the pocket calculator people would ever really cut it at the 'serious' end of the keyboard market, particularly after the domestic monstrosity that was last year's Symphonytron modular home organ. However, it would now seem that Casio have put these abberations firmly behind them: the CZ101 is the first of a whole range of pro gear that'll emerge during the course of 1985, and brings with it a new synthesis technique by the name of Phase Distortion.

The 101 has only a four-octave mini-keyboard and a rather awkwardly-placed bend wheel, but the fact that it's MIDI-compatible over five octaves means this will be a limitation only to the first-time MIDI buyer. And yes, a standard-sized keyboard variant - the CZ1000 - will be available in the Spring for about £50 extra, though personally I'd rather put that money towards another MIDI instrument with a five-octave keyboard span, since it's the sound of the 101 that's the really worthwhile thing (as we'll see later). Depends on whether you intend adding to your collection of MIDI keyboards, I suppose.

PD in Theory

That highly desirable sound comes from a new and Casio-developed synthesis process called Phase Distortion. How does it work? Well, imagine a simple waveform - a sinewave, say. Store it in ROM, read it out, and as you do so, alter the phase angle during each cycle so that a distorted version of the original waveform is produced. Figure 1 shows a cosine wave (generated when the phase angle is read out at a constant speed) between the values of 0 and 2π. Change the speed so that reading out is faster between 0 and π than it is between π and 2π (ie. faster in the first half-cycle than in the second), and distortion starts to become evident.

Figure 2. Phase angle no longer linear.
Figure 1. A cosine wave written into ROM and read out in linear form.

Figure 3. More of the same.

As you can see, the result of this distortion is to displace the position of the positive peak towards the front of the cycle, a process not entirely unlike changing the width of a pulse wave (but not entirely like it, either - Ed). The logical conclusion of this process tends towards a sawtooth wave, as the difference in readout speed is increased (Figure 3).

As you probably already know, a perfect sinewave consists of its fundamental frequency and nothing else. More complex waveforms add various harmonics of the fundamental, and one of the most intricate of these that succeeds in going about its business without actually losing the level of the fundamental is the sawtooth, which contains all the harmonics in inverse proportion to their number.

Now, the beauty of the Casio system is that these changes in readout speed can be implemented as you play the keyboard. This is accomplished by an envelope known as the DCW (methinks it stands for Digitally Controlled Waveshape), which can be considered the PD equivalent of a filter envelope. It operates like this. When the envelope begins, the waveshape is a simple one - let's say the sinewave again. As the envelope opens, phase distortion is increased to a user-preset level, so that the waveform produces an increasing quantity of higher harmonics in much the same way as a low-pass filter.

PD in Practice

What this means in terms of sound is that, unlike the FM principle by which filter sweep effects can be rather tricky to create, a PD synth can actually make an approximation of analogue-type sounds. However, seeing as digitally-stored simple waveforms of high resolution are still the basic building blocks from which sounds are created, the 101's outstanding sonic characteristic is one of cleanness and purity - the output lacks analogue harmonic distortion.

Any comparisons with FM are probably misleading, but sound-wise the CZ101 excels in the same areas as Yamaha's DX polys - natural 'acoustic' textures, especially those with percussive envelopes.

Full marks to Casio, though, for the way in which they've made their technique accessible to the musician. The layout of the panel is logical and easy to get to know, while a liquid crystal display gives a readout of each parameter value, these being selected by switches entirely separate from those used to effect program changes. Hence getting the synth to respond to your patch editing wishes is a lot simpler than it is on those instruments (DX7, Poly 800, SixTrak) that force you to keep switching between program and edit modes.

What makes editing more straightforward still is that the results of parameter changes are a lot more predictable than they are on the DXs. Within half an hour of seeing the 101 for the first time, I was altering values with total confidence in what the procedure would achieve.

"The voices were good enough to convince me there should be plenty of sonic mileage to be got out of Phase Distortion."

Two different modes allow the Casio's eight voice channels to be used for eight-note polyphony (one channel per voice) or four-note operation (two channels per voice). Each channel has entirely separate envelope and PD controls.

Figure 4. A typical DCW envelope setting, with points (a), (b) and (c) showing the wave output at that point of the envelope.

Eight independent waveforms are available in total (they're displayed diagrammatically on the front panel), and each DCO has two assigned to it, one to provide the sound source and the other to generate the Phase Distortion. Like all the other envelopes on the 101, the pitch envelope can have up to eight steps, each with its own variable rate and level (can't help thinking I've seen those phrases somewhere before). As I've already mentioned, the DCW controls the PD-induced harmonic content level, and is made up of two sections - a key follow to allow the effect to be varied up and down the keyboard, and a further eight-step envelope (illustrated in Figure 5) to control the amount of the effect. Use just four of the envelope steps and you can imitate a standard VCF ADSR, and Figure 4 shows how the effect of a filtered sawtooth can be induced. At the maximum point, the PD has turned the sinewave (ie. the fundamental) into a sawtooth, but as the filter closes again and the waveform turns back into a sine, the harmonics are reduced in number.

Figure 5. An envelope using all eight of the CZ101's programmable steps.

The DCA or amplifier section has the same key follow and envelope controls as the DCW, and these allow volume to be varied across the keyboard and complex envelope delay effects in addition to the standard ADSR variations. For instance, repeats can be triggered by reducing one of the eight levels to zero and opening the envelope again at a later stage.

If you're in four-voice mode, the two channels can be tuned apart in one of three amounts - fine, semitone, and octave. And, logically enough, each of the channels can be assigned not only different waveforms but also different DCW and DCA effects. This means that 'doubled' voices are easily created, and if you're really clever, you can manipulate the individual key follow parameters so that the 101's keyboard can be split with one voice at the bottom and another at the top, though be warned - the sounds will still merge in the middle.


The CZ101 holds 16 Casio factory presets (these are not erasable) and enough space for you to store another 16 of your own. The factory voices I found in the review sample are not, apparently, those that'll appear on machines when the model is properly launched in the UK towards the end of January. And a couple of good flute and piano sounds apart, that's probably no bad thing. Still, amongst the user-programmed sounds (courtesy of Casio demonstrator Richard Young), was an excellent clav that made use of the 101's built-in digital ring modulator (if I had my way, this facility would be standard on all synths, no matter what their country of origin), and the remainder of the voices in this bank were good enough to convince me that there should be plenty of sonic mileage to be got out of Phase Distortion.

And once you've exhausted the 101's program memory space (no, it isn't enormous, but how many keyboard players actually need the 128 memories provided by other machines?), Casio will be happy to supply you with cartridges that hold a further 16 - they're due to be £29.95 each.

Casio have also blessed their baby with an excellent implementation of MIDI. As I've said, five octaves of pitch are recognised (if you're using a very long MIDI controlling keyboard, the Casio duplicates its top and bottom octaves to avoid any dead areas), as are pitch-bend and program-change enable and disable functions. You can switch remotely between Poly and Mono modes (the 101 can receive and transmit on any of 16 MIDI channels), and I only wish other Far Eastern manufacturers had entered the MIDI minefield with the same dedication as the CZ's designers - it would have made interfacing life a lot easier for all concerned.


If there's one fact that almost escapes unnoticed about this new Casio - such is the degree of competence and innovation within the machine - it's that it is remarkably good value for money at only £395. It's probably the least unexpected aspect of the machine's specification, given Casio's reputation for offering consumers a little bit more for their greenbacks.

So yes, I more or less expected that when Casio produced a professional polysynth, it would carry an RRP calculated (no pun intended) to make some of the competition look very silly. What I wasn't expecting was that the synth would employ a completely new method of sound synthesis, and that its designers would succeed in making that method so easy to apply from the word go.

As I see it, the only problem facing Casio (apart from the possibility of the UK division experiencing supply problems) is one of trying to convince pro players to accept an instrument from a company with a somewhat tarnished serious keyboard reputation. Isao Tomita, who played the CZ101's prototype ancestor at Ars Electronica earlier in the year (see report elsewhere this issue), has blessed the production model with the name Cosmo. From where I'm standing, that's something that ought to be changed as soon as possible if the marketing strategy isn't to deter potential purchasers before they even get the instrument out of its box.

You'd be right in thinking that Casio have produced some decidedly unprofessional products in the past, but wrong in deciding that the CZ101 is one of them. Because this is the keyboard that changes everything.

Further information from Casio Electronics, (Contact Details).

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Simmons SDS EPB

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


Electronics & Music Maker - Jan 1985

Scanned by: Stewart Lawler

Gear in this article:

Synthesizer > Casio > CZ-101

Gear Tags:

Digital Synth
Phase Distortion

Review by Paul Wiffen

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