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Understanding the DX7 (Part 1) | |
Article from Electronics & Music Maker, April 1984 |
DX7-owner Jason Chapman and the first of a new series on how to find your way round these revolutionary Yamaha synthesisers. Part 2 next month.
Although Yamaha's DX series keyboards have received nothing but praise for the quality of their factory-programmed voices, they remain something of an enigma where user-programmability is concerned. Not to put too fine a point on it, there seem to be very few users indeed who have managed to exploit their DX to the fullest. DX7-owner Jason Chapman has worked his way painstakingly through his machine's workings, and in the first of a new series, guides us through a few simple experiments that should shed a little light on how the DX keyboards go about their sound-generating business.
What I am going to attempt in this article is to lead you through a few practical experiments to demonstrate how the basic building blocks of the DX7 - the Operators - are used and what Frequency Modulation does. I'm going to assume you've read through (or at least glanced at) the Yamaha manual and that you can read the legends on/above/underneath all the pressure pad-type buttons. Note that some of the keypads have up to four different functions (hence all the different legends!) - I will refer to a keypad by its colour and the legend in question eg. 'the purple 'EDIT/COMPARE' keypad' actually has the '-' symbol on it and the 'EDIT/COMPARE' legend in white above.
Most of our playing about is carried out in Edit Mode where the user can not only edit or change the voice parameters to create a new voice but can also view them at his leisure. By altering parameters in a controlled and logical fashion and observing how the voice changes, you should, with luck, learn how to exploit the incredible potential of the DX7 a little more fully.
To get into Edit Mode you simply press the purple 'EDIT/COMPARE' keypad which causes the display to change from showing voice identification data to showing information about the parameters of that voice.
To understand how the sound is built up from the Operators we first need to understand the Frequency Modulation technique used in the DX range. There is a good explanation in the DX7 manual so have a look at that and then try the experiments below to see the theory in action...
You should have gathered that sounds on the DX range are produced by connecting together Operators in various configurations called algorithms. In this demonstration we will use just two Operators (out of the six available on the DX7) and connect them in only two configurations, both of which are simple sub-parts of the Algorithms available. These two simple configurations form a complete basis for the usage of Frequency Modulation techniques.
OK, let's get to work. What is an Operator? Have a look at the diagram (Figure 1).
You might think for a moment things are beginning to look a trifle complicated but, fortunately, we can look on the Operator as being a sort of simple monophonic synthesiser with one module missing. The module the Operator lacks is the equivalent of the Voltage Controlled Filter - we shall see why it is not present shortly. Another difference worth noting is that the oscillator is only capable of producing a sine wave output, so no complex waveforms overflowing with rich harmonic content - well, not from one oscillator on its own anyway.
So, the first part of the practical work is to use one Operator and in doing so understand its capabilities by relating it to the design of a very degenerate monophonic synthesiser. In fact, to show how two Operators combine in the two basic configurations in the simplest way, we ignore envelope generation completely and concentrate on pitch control and, subsequently, waveform generation.
Single Operator Demonstration
The first thing we have to do is get just about everything switched off so that we are playing with only one operator. Try the following:
- press the yellow 'FUNCTION' keypad
- press the green 'VOICE INIT' keypad
- reply to the question 'VOICE INIT?' (in the display) by pressing the green 'YES' keypad
- reply to the question 'ARE YOU SURE?' in the same way
- press the green 'OUTPUT LEVEL' keypad
- press each of the green keypads 2 through 6 once to turn all but operator 1 off - your display should look like this:
- get into 'FIXED FREQ. (Hz)' as described above
- press the green 'FREQUENCY COARSE' keypad
- press the green '+1' keypad until the display bottom line reads;
- get into 'FREQUENCY (RATIO)' as described above
- press the green 'FREQUENCY COARSE' keypad
- slide the data entry slider completely towards you
- press the green 'FREQUENCY FINE' keypad
- move the data entry slider until the bottom line of the display reads:
In exactly the same way as we use two drawbars on an organ or two oscillators on a synth, we can mix the output of two oscillators (ie. Operators as we are using them at the moment), and by altering their pitch and amplitude relative to each other, we alter the overall harmonic content of the mixed output. On a normal drawbar organ we use the drawbars to alter the relative amplitudes of the harmonics but we cannot change the pitch of the individual drawbar outputs - on the DX7 we can!
The study of how the harmonics of a sound work together to create its timbre is beyond the scope of this article - I'll let another experiment explain things instead:
- do a 'VOICE INIT'
- turn Operators 2-6 off (press green keypads 2-6)
- press the green 'OUTPUT LEVEL' keypad
- you should have the basic one operator sound, ie. display reads:
This uses two Operators, the output of one Operator modulating the pitch control of the second. This method of using two oscillators is by no means unique to Yamaha FM - most really 'fat' sounds to be heard from synths such as the original Minimoogs are based on the same configuration. What years of Yamaha research has added to FM is the control that makes FM techniques of genuine practical use.
Let's get this part of the show on the road:
- do a 'VOICE UNIT' as above
- turn off Operators 3 through 6
- press the green 'OUTPUT LEVEL' key - you should have:
In the next few articles we'll analyse some of the Yamaha's pre-programmed voices in the hope of shedding yet more light on how to control the DX7. And we might even try setting up a voice or two of our own...
If you have any particular questions you would like me to (attempt) to answer on the wonderful world of the Yamaha DX series please write to me, care of E&MM, and I'll do my best to dig up some answers!
Read the next part in this series:
Understanding the DX7 (Part 2)
(EMM May 84)
All parts in this series:
Part 1 (Viewing) | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7
Fun in the Waves (Part 1) |
The Ins and Outs of Digital Design |
Constructing A Trigger Delay |
Technically Speaking |
Add Muting, Decay/Release Isolation and/or End of Cycle Triggering to Your 4740 |
The Lazy Guide To Good Synth Sounds |
![]() Loony Toons |
Music Modules for NON-Keyboardists |
Patches |
Back to Basics (Part 1) |
Sounds Natural - The Acoustic Guitar (Part 1) |
A Handy Way To Solve Sticky Control Problems |
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Feature by Jay Chapman
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