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It's Cee Zee! (Part 1)

In Part One of this two-part Programmer's Guide to the Casio CZ range of synthesizers, Phil South maps out the territory beyond the factory presets.


In Part One of this two-part Programmer's Guide to the Casio CZ range of synthesizers, Phil South maps out the territory beyond the factory presets.

You'd probably not be surprised if I told you that around fifty percent of all Yamaha DX7s returned to the factory for repair, still have their factory preset sounds intact after many months of use. But what might raise your eyebrows, and indeed anything else you might care to lift in surprise, is that in quite a few cases the same can be said of Casio's CZ range of synthesizers. The reason for this lack of adventurous spirit on the behalf of the CZ owners is odd, because the whole point of the Casio digital synths, I always thought, was that they were easier to programme than the FM type, being more like the kind of analogue machines that aged synthesists (yup, me too) were used to!

But it seems that you can't please some of the people all of the time, and the Casios do suffer from a lack of the 'twiddle factor'.

'Twiddling' is the technical term for when somebody moves a tangible control knob on a device and on hearing the resultant squeal says, "Hmm, fascinating Captain, but I think it's logical to add a little more ring modulation." It's a question of feedback, and it's how we all learned what we know about synthesis. Now being able to twiddle a knob and produce an effect is something we're unable to do in quite the same way on a Casio synth (the same goes for 99% of all digital synths), and constructing a sound from scratch requires forethought, and more attention to the digits on the LCD display than to those on the end of your arms!

In this article, and the one to follow next month, I shall be taking you through the basics of sound generation, with specific emphasis on how this relates to Phase Distortion Modulation, the method of sound production used in the CZ synths. If you think you've seen all this before, just hold it right there. Don't be put off by what looks like familiar territory, because you might just miss the pertinent fact, or way of working, that stands between you and full control of your CZ synth. Think of it as a sort of foundation course for what is to follow. Okay, let's roll up our mental sleeves and see what's under the hood. Here, pass me that wrench...

WHAT IS PHASE DISTORTION?



Your understanding of Phase Distortion Modulation (PDM for short) depends on the kind of thing you're used to. As a method of sound synthesis, PDM shares some common attributes with FM synthesis (yes, even the DX7) and all the old analogue synths. The way different parameters are programmed on a CZ synth is almost identical to the way they are programmed on FM synths (and for the sake of argument, for 'FM' let us read DX). In a DX synth you've got a whole bunch of 'operators', which you programme digitally by stepping each parameter up or down, digit by digit, say from 0 to 15. From then on it's the manner in which these 'operators' are lashed together in different combinations ('algorithms', to the aficionados) which give you the rich and complex timbres we know and love as 'the DX sound'. So, the two synths use a similar programming method, but there are far fewer parameters to set on a CZ, because the two instruments create their sounds in very different ways.

FIGURE A

In order to better understand the creation of sounds using PDM, we have to first look at waveforms and at how their shape is meaningful to their sound. Study, if you will, Figure A. Represented are two simple waveforms - the simplest of all, in fact - a sine wave and a cosine wave. It's common practice amongst the physics and electronics fraternities to measure waveforms using a standard method that isn't dependent on time, or on the individual frequency of the wave in question. (With me so far?) What this means is that you can accurately measure, and therefore categorise and study, the shape of any waveform without having to mess around with finding the right scale to work on if the wave has a very high frequency. The method utilised by these clever people, and now by us, is a mathematical one. (Now I know the very mention of maths in polite conversation is enough to send anyone off for unexpected country walks, but relax! It's very simple stuff, I promise.)

We refer to points in a cycle of the waveform in degrees, like the increments of a circle, with a full cycle being represented by 360 degrees. So, 180 degrees is exactly halfway through a cycle (see Figure A) and 90 degrees is a quarter cycle, and so forth. Right, so now that we have a way of measuring chunks of a waveform, what are these chunks called? The correct term is the 'phase angle', and this brings us to the nub of the question "What is Phase Distortion?". Simply expressed, Phase Distortion is altering the position of these points along the waveform, distorting them out of shape.

FIGURE B

The way the Casio synths perform this miracle of maths is quite interesting. A cosine waveform is loaded into ROM in the synth (I bet you didn't know that the CZs were fine little computers too!) as a set of numbers, representing the points in just one cycle. These are then read over and over to the CZ's amplifier, forming a seemingly continuous oscillation. (This is a clever trick, often used in digital oscillators!) Now all the computer in the synth has to do to output different pitches is to read the information at a faster or slower rate, just like sound samplers do. Tricky eh? Now where Phase Distortion really comes into its own is that when you are reading out the waveforms, you can also make changes to the readout speed within the waveform! Let's see what this means practically...

Notice the cosine wave in Figure B. This is an undistorted cosine, containing no extra harmonics and no artificial flavouring, just the naked fundamental frequency. The phase angle is a dead straight line, due to there being no change in the speed of readout during the cycle. Now shift your attention to Figure C. This is what happens to the wave when you read out data faster between 0 and 180 degrees (the middle of the cycle) than between 180 degrees and 360 degrees. As you can see, the phase angle has distorted, causing the waveform produced to take on more of the shape of a sawtooth wave.

FIGURE C

The distorted waveform now contains many harmonics not present in the original. So as you can see, the greater the effect of the phase distortion, the brighter the sound, due to the addition of more harmonics.

MAKING A SOUND



The single most significant advantage of Phase Distortion Modulation over Frequency Modulation (FM) is that it gives you ease of access to the harmonic content of a sound, and ease of control over the harmonic structure. Using envelopes to dynamically change the phase angle during a sound, enables you to vary the timbre (tone) of a note while it is being played, imitating changes in timbre that appear in natural sounds. In fact, this process is very similar to the job done by the filter envelope in an analogue synth. The CZ series have been designed to function like analogue synths, and the similarity is evident in the layout of the separate control elements. Although digital in construction, the way you take an oscillator, treat it and then amplify it using envelopes is oddly familiar. These three phases corresponding to pitch, timbre and loudness.

The pitch, as we've seen, is a straight reading of the waveform information faster or slower for a higher or lower frequency, respectively. The timbre is affected by distorting the initial waveform to produce a more complex harmonic series, and this can be done over time, where the timbre changes through the duration of the sound. The amplification, or loudness, of the note is governed by a simple amp envelope generator (EG). These, then, are the primary elements of the CZ sound.

So the first thing you must choose, when building a sound from scratch, is the initial waveform. There are eight basic waveshapes to choose from on the CZ synths, and here is a quick reference guide to them:

Sawtooth: By far the most common waveform, in which all the odd and even harmonics are present. As such it has a bright sound, making it very good as a starting point for the creation of brass or string sounds.



Square Wave: This has only the odd numbered harmonics present, like the 3rd, 5th, 7th, 9th... On its own, it has a hollow, tube-like quality, best suited to synthesizing woodwind instruments.



Pulse: Like the pulse wave we know and love from our analogue days, this is the little brother of the sawtooth wave. All the harmonics, but lacking the strong fundamental, having the effect of making it thin and reed-like.



Double Sine: This is the first of the CZ's hybrid waves, being kin to the pulse but with a stronger fundamental. Not as rich and fruity as the sawtooth, because it is missing some middle harmonics.



SawPulse: Just to confuse the issue still further, here is the sawpulse, a hybrid of the sawtooth and pulse waves. Brighter than the sawtooth, but more powerful than the pulse. Very brassy.



Resonance I, II, III: These waveforms imitate the resonance you used to get on Moog synths when you turned the filter way up! As the CZs don't actually have a dedicated filter, these waves digitally recreate the sound of accentuating those very high frequencies. Their effect varies in proportion to the amount of DCW envelope you give them.



So these are the basic waves you can start with, before you begin distorting them. But wait a second, there's more!

You can also use combinations of them. For instance, you might like the sawtooth, but think it needs a bit more of the characteristics of the sawpulse. Well, all you do is combine them, in the Waveform menu in the DCO section. But, further than this, you can do the same in the second DCO, making the total combination of differing waveforms up to four, and just blend them using the '1+2' mode in the Line Select section.

WHAT'S THIS BUTTON DO?



Now that we've covered the creation of sound on a theoretical level, let's move on to the actual way you, as a programmer, can do it for yourself. For the purposes of this article, we are taking the simplest synths - the CZ101 and CZ1000, as our examples, but the principles apply equally to the whole of the Casio CZ range.

The CZ front panel is divided roughly into three parts: the Program Section, the Effect Section, and the Parameter Selection Section. (Hard to say that with a mouthful of crisps!) Let's look at each in turn.

Parameter Section: This is where you actually programme your sounds. Like the old analogue synths, the controls are easily divided into oscillator, filter and amplitude functions. Only in this case, since they're digital, they're called DCO, DCW and DCA, instead of the voltage controlled equivalents - VCO, VCF and VCA. As there are two digital oscillators, so you have two banks of controls marked DCO1, DCO2, DCW1, DCW2, DCA1, and DCA2. Attached to these controls, and routable through them, you have three other controls: Vibrato - which does just that; Octave - which switches the available range up and down, giving you six octaves to play with; and Detune — a way of altering/offsetting the pitch of the two digital oscillators, giving you a method of producing chorus/flanging effects. There is also a Line Select button, which determines which oscillators are active (either 1, 2, 1+2 or 1+1), meaning you can play each oscillator on its own, with the other one, or play DCO1 doubled up on itself. Attached to this section are two other controls probably better suited to the Effects section - Ring Modulation and Noise. These can only be heard when you select either 1+2 or 1+1. But more about them next month.

Program Section: Located here are the controls for selecting the different voice programs (sounds) stored in your CZ. But then if you've spent the last couple of months selecting the factory presets from here, you already know what this section does. But for the sake of completeness, let me say that these buttons select which sound you want to play, from either Bank, and from either Preset memory, Internal memory (this is where your own sounds should be stored), or a ROM cartridge ("here's one I prepared earlier!").

Effects Section: Arranged in an L-shape around the Program Section are the keys which programme the effects and amount, or lack, of them in your sound. The most interesting feature is the Tone Mix, where you can blend two sounds together and play them as one - a bit like adding a monophonic expander to your synth! There are controls here, too, which define the amount your pitch wheel will bend, whether the vibrato is on or off, as well as keys for precisely tailoring the amount of time it takes to glide, or portamento, when you change notes.

SUMMING UP



So that's about it. We've covered the theoretical and the physical aspects of the problem, which neatly leaves us with the aesthetic and technical considerations for next month, when we'll take more of a 'hands-on' approach to programming CZ synths and show how you can come out with an original sound. As far as programming is concerned, the CZ range are the perfect instruments for synthesists used to analogue machines who want the range of timbres offered by digital equipment.

In our next episode we'll delve deeper into the ways you can use these glorious synthesizers to make your own sounds, and explain why their above-average MIDI capability makes them a worthwhile choice for even the most advanced synthesist.


Series

Read the next part in this series:
It's Cee Zee (Part 2)



Previous Article in this issue

The Holistic Author

Next article in this issue

Oberheim DPX1 Sample Player


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 - Jul 1987

Topic:

Synthesis & Sound Design


Series:

Programmer's Guide to the Casio CZ

Part 1 (Viewing) | Part 2


Feature by Phil South

Previous article in this issue:

> The Holistic Author

Next article in this issue:

> Oberheim DPX1 Sample Player


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