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Yamaha DX-7 Synthesiser

FM isn't just for your radio. Yamaha take it to digital keyboards. Prof. Dave Crombie expounds (his case comes up next week).

Programmable Algorithmic FM Digital Synthesis is what this month's piece is all about. And without doubt this is the most exciting new development of the decade (even more so than the Austin Morris Maestro). (Never! Ed.) Yamaha have pretty well made a total commitment to FM synthesis, so they hope it will catch on in a big way; judging by the performance of this new DX-7, they shouldn't worry.

What is FM Synthesis?

We've come across FM Synthesis in earlier Yamaha products - the GS-1, GS-2, GF-20 and CE-25, but only with the new DX range have Yamaha made these instruments programmable.

FM stands for frequency modulation, and these instruments do not employ the more traditional (if that's the right word for technology that's been around barely 15 years!) VCOs, VCFs, and VCAs used by analogue synths. Instead they use sine waves modulating other sine waves to generate complex timbres.

If you're familiar with the conventional synthesizer set up, you've probably noticed that when you cross modulate one oscillator with another, (both running at audio frequencies) you get a very complex rich sound - often rather bell-like. Well, Yamaha, following considerable research, have used this concept of cross modulation to create a whole new technology. FM Synthesis uses sine waves acting on other sine waves as the cross modulating generators, and by accurately defining the amount of modulation and the frequencies of the two signals it is possible to generate a vast assortment of complex musical timbres.

So in essence that's how FM Digital Synthesis works. This might be a fine system for producing nice sounds, but programming them isn't so straightforward - that's why Yamaha originally released only preset instruments. The new DX keyboards are fully programmable, and in order that we musos might have a chance of controlling this new system, Yamaha developed a new concept in voice programming; and this is where the 'algorithms' come on the scene. Those familiar with computer programming should be aware of this term; an algorithm is basically a graphical representation of a signal or option path - you know the sort of thing:-

1) Take a playing card;
2) Ask for another card;
3) Add their numerical values together;
4) If they total less than 16 (say), then return to 2);
5) If they total more than 21 then BUST (end);
6) If between 16 and 21 then STICK.

This is a very simple algorithm for playing pontoon, and from it it is possible to write a computer programme more easily. With the DX machines things are a little different, as we shall see.

Figure 1: An algorithm of six operators

Take a gander at Figure 1. This shows one of the DX-7's algorithms. You will notice that there are six boxes each called an 'operator', and each operator consists of a sine wave generator and an envelope generator. All these operators are identical in format, but those along the bottom are known as the carriers (in this algorithm they're 1, 3, and 5) because they are the ones that actually make the sound. Operators 2, 4, and 6 are used to modulate the carriers, hence they are known as modulators. It might make things clearer if we consider this system in more conventional terms — so Figure 1b shows this algorithm as a series of sine wave generators, VCAs and envelope generators — although in fact the contouring of the sine waves is done digitally, and not with the aid of analogue circuitry. Remember that the modulators are modulating the frequency of the carriers not the amplitude.

So, we can see that we have three almost identical configurations for each pair of operators. (Don't worry about the loop of operator 6). And this corresponds to having three separate voices in parallel.

Figure 1b: Conventional representation

Let's consider one pair of operators — 1, and 2. It is possible to switch off any operator at the touch of a button, so as operator 1 is the carrier, let's look at that first. To get anything out of the instrument you must have at least one of the carriers 'ON' — makes sense doesn't it? If you modulate nothing you get nothing. So you select the pitch and envelope of operator 1, and you get a simple sine wave tone with the given amplitude contour. If we then introduce the modulator, operator 2, we find that varying its frequency produces a difference in the timbre of modulator 1 and by using the envelope generator to contour the modulation we can introduce a timbral variation during the course of the note. It's a bit like using an envelope generator on a VCF, but far more versatile. So we've managed to set the pitch of the sound by setting the frequency of Operator 1; the timbre by the frequency and envelope of Operator 2, and the amplitude contour by the envelope of Operator 1. Thus we've managed to determine the three principal elements, pitch, timbre and loudness, that are used to synthesise any sound. Simple isn't it?

So far we've used just two operators, other pairs can be used to construct other sounds, which can then be layered on top of the original one, providing a really full, complex, versatile... I've run out of adjectives... signal.

You may still be wondering about operator 6 with that loop. All the DX machines have one operator that can be fed back on itself. A consequence of this feedback is to produce unpitched noise like sounds, so an operator with feedback can be used rather like a white noise generator, although the feedback can be switched off.

Now you may be under the misapprehension that there are only six operators in the whole machine — you'd be wrong, because so far we've been dealing with just one of the DX's voices. The instrument is a 16 note polyphonic, and it is possible to arrange any of these programmed sounds using 16 note polyphony — which can't be bad.


We've been considering the basic fundamentals behind the DX's Digital Algorithmic FM Synthesis, now let's look at the DX-7 itself in more detail.

The initial knockout blow comes when you learn the price of this instrument. At £1299 it is ridiculously cheap. You couldn't have imagined that an instrument of this versatility and power could have been produced for anything like this price, even as recently as a year ago. The DX-7 is going to be a winner, and I reckon would be well worth the money at £2000. There is a DX-9 with just four operators at £899, and a DX-1 will soon be available at around £6500, but we at MUSIC U.K. reckon that the DX-7 is the proverbial "bee's knees". The unit is not as cosmetically pleasing as its performance. The casework is plastic (even the end cheeks), and Yamaha have gone more for the sombre black than the somewhat more fashionable grey look, although I suppose the control buttons are colourful. But appearance isn't the most important thing here.

The keyboard is, as stated, a 16 note polyphonic, and it is velocity and pressure sensitive, and the effect of these two sensors is programmable. The keyboard has a smooth silent action that is fairly light and well suited to the role of synthesis.

The control panel, like the terminology, looks complicated, but in fact isn't. To keep costs at a reasonable level Yamaha have used membrane switches as the main control medium. Generally these switches, which are basically touch pads forming part of the graphics of the panel, are a bit of a b***** to use, as you never really know whether you've actually activated the switch or not. But these ones actually move a little, and you do feel more confident when using them. There's a bank of 32 switches that adopt a variety of functions - some are used for up to four different jobs. In the centre of the control panel is a LED two digit display indicating which of the 32 different programmes is currently selected; and a 32 character liquid crystal display provides a mass of programming data, and guides you through the programming and sound creation minefields. Eight more membrane switches to the left of the display determine the functions of the 32 switches, and whether you are using the internal memory or plug-in cartridge facility. The DX-7 doesn't have a cassette interface, instead you receive two plug-in ROM (read only memory) cartridges with the instrument which contain data for 120 different preprogrammed sounds, and for a modest outlay you can purchase a RAM cartridge (which actually contains an EEPROM - electrically erasable programmable read only memory) onto which you can put 32 of your own sounds. The DX keyboards use incremental control for programming, thus you select a parameter that you wish to alter by activating one of the 32 membrane switches, and the value of it can be adjusted from 0-99 and displayed in the LCD window. So every parameter can be extremely accurately set.

Two performance control wheels are located to the left of the control panel for those who just love to 'choke' their keyboards. The pitchbender is centre sprung so it always returns to the correct tuning when released (personally I prefer the centre-detente/notch system). Both the pitchbender and the modulation wheel are programmable.

Figure 2: Sample algorithms

Figure 3: Envelope Generator Format

I don't have the space to detail all the DX-7's operational assets, but certain elements should be highlighted. We've mentioned the concept of the algorithm with an example; on the front panel are drawn 32 different algorithmic configurations - figure 2 shows a few of them. Any of these can be used to build up a sound, though it takes a bit of experience to know exactly which algorithm is best for achieving a desired result. But remember that the bottom row indicates the number of carrier operators, and consequently you can determine from this the number of individual signals that can be combined in a sound. For example algorithm 32 has all six operators running in parallel with no modulators. This could be compared to having six sine wave generators available, which could be set at any pitches. If you set them at harmonic intervals you would have a set up rather like that of a drawbar organ. Also depicted on the control panel in graphic format is the envelope generator. This is far more elaborate than the old ADSR system. Figure 3 shows it more clearly. You can set four level points, and four rates - ie, the time the envelope takes to move between the level points. This makes the envelopes extremely versatile (fig 3b shows some 'possibles') and also very accurately definable. A final diagram on this front panel is headed 'Keyboard Level Scaling'. The DX-7 doesn't actually have a splittable keyboard as such, but sounds can be balanced across the keyboard, so they cross fade into one another. This is quite a complex system to explain, but if I refer to one of the original preset sounds, 'Train', then the scope of this facility may become apparent. 'Train' uses the same algorithm as shown in figure 1 and has a puffing sound set across the entire keyboard (Operators 5 and 6), with a clanging bell (Operators 1 and 2) assigned to the top end of the keyboard and a whistle (Operators 3 and 4) to the lower. The bell has a fixed pitch whose amplitude dies as you move down the keyboard, whilst the whistle's pitch increases and amplitude decreases as notes are played moving up the keyboard. Pretty hot stuff.

Figure 3b: Possible envelope shapes

The DX-7 accepts Yamaha's BC-1 breath controller for yet further control over the sound, and a host of footswitch and pedal sockets can be used to control portamento, sustain, modulation, level etc. All the DX machines feature the new MIDI interface bus.


The preset voicings of the DX-7 are stunning. The Flutes have all the characteristic chiffs and there's a Fender Rhodes sound that responds to harder playing by dirtying-up and distorting just like the real thing. There are great String and Brass voicings, and sounds like Tympani and Clavinet have you completely fooled. But when you start programming the thing you realise the potential of the system, and when you get to such complex algorithms as, say, no. 18 - fig 3, you realise how much scope there is for an instrument of this nature.

Don't be put off by the initial complexity of the product - you've always got the presets to fall back on, and when you've finally mastered programming (the manual explains things pretty well), you'll never want for a sound. The DX-7 has no gimmicks such as an arpeggiator or sequencer - the MIDI bus gives you scope to expand along those lines at a later date. This is truly a musician's instrument that is incredible value for money, and gets my vote for instrument of the year (maybe even of the decade, but I should air a degree of restraint).

Likes: Dislikes:
Price Appearance
Versatility Plastic case
Sound quality No stereo facilities
Performance controls/touch keyboard
Control panel graphics
Cartridge memory
The concept

YAMAHA DX-7 Synthesiser. £1299


Awarding our second MUSIC U.K. STAR BUY in two months is, frankly, an odd feeling! Normally many months elapse between STAR BUYS — in fact we've only awarded six in almost two years. But what can you do when you are faced with two fabulous products in two months? Stick to your guns and give credit where credit is due is the answer. And credit is certainly due to the latest keyboard introduction from Yamaha - the fabulous DX-7.

As regular readers will know, the MUSIC U.K. STAR BUY AWARD is our way of telling readers about those very rare products which impress us as offering outstanding value in terms of quality or price. The DX-7 scores on both counts.

We award a MUSIC U.K. STAR BUY without any prejudice on account of advertising and regardless of commercial considerations. The product is allowed to carry the exclusive MUSIC U.K. STAR BUY AWARD swing ticket, supplied free of charge to the manufacturer or importer. They also have the right to use the MUSIC U.K. STAR BUY AWARD logo in their advertising and promotion in any publication or medium whatsoever. The logo may only be used on the product which has won it.

The idea behind the MUSIC U.K. STAR BUY AWARD is to single out products which, in our opinion, excel even at a time when there are many good products around. The STAR BUY winner is always something very special and we want to draw attention to it and encourage competition among manufacturers to produce better products at better prices. Competition to win a STAR BUY is intense - and that, of course, is the idea. If it makes manufacturers try harder then it's done half its job. If it leads you to consider better products, then that's the other half completed!

The Yamaha DX-7 is a worthy winner. The technological breakthrough achieved by Yamaha in making programmable digital FM synthesis available at such a relatively low price is remarkable and shows how their considerable investment in research and development has paid dividends - dividends which make the DX-7 a marvellous product at a very good price.

The Yamaha DX-7 is the first keyboard to be awarded a MUSIC U.K. STAR BUY and perhaps that's the best way of explaining just how impressed we are. Congratulations, Yamaha, your DX-7 is a fine achievement!

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May Competition - Winners Take All!

Music UK - Copyright: Folly Publications


Music UK - Aug 1983

Review by Dave Crombie

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