The new FM synthesis
Mark Jenkins expounds on the delights of FM synthesis.
The DX7 is destined to be one of the keyboard classics along with the Fender Rhodes, the Mini Moog and the Wasp. In addition to joining this hall of fame the synth is going to overturn the conventions of instrument design, because it uses the latest generation of FM sound production, and so differs in many ways from the run-of-the-mill analogue synthesiser.
FM technology was developed for the GS synth range, which reflected the cost of the R&D involved and in addition to being expensive were bulky, relatively limited and programmed by computer-prepared magnetic cards. The sound quality was outstanding however, and Yamaha thought it worth the effort of making the FM system a more commercial proposition. The DX7, smaller DX9 and the larger forthcoming DX1 are the result of that development.
The FM system was described by John Chowning, patented by Yamaha and licensed to NED for the Synclavier. Conventional analogue synthesis relies on filtering down simple waveshapes and so cannot progress much beyond these shapes, but the FM system uses two simple waves — sine waves — and uses one to modulate the other. The product is a complex waveform which can't be obtained on an analogue synth and which can only be stored in larger computer synths by using large amounts of expensive memory. Frequency Modulation therefore depends on using two waves, a Carrier and a Modulator. The DX7 has six sine wave generators or Operators, each one being capable of use as a Carrier or a Modulator, and so three simultaneous sounds (or one complex sound with three main components) can be created.
The six Operators can be arranged in various ways. For instance it is possible to modulate a carrier more than once at different frequencies. The ratio of the Carrier and Modulator frequencies helps to define the tone of the sound produced. Each different way of arranging the Operators is known as an Algorithm. If you want a thick, complex sound, choose an Algorithm with three Carriers each only being modulated once. If you want a thinner sound with more different types of control, use an Algorithm with only one or two Carriers being modulated several times.
Because the FM system produces complex waveshapes it is much better at simulating acoustic sounds than an analogue synth could be. Yamaha have capitalised on this capability by adding various performance features and musically useful effects, which turn the initially imposing DX7 into a real keyboard player's keyboard. Although initial reactions to the DX range sounds have been very good, the fact remains that keyboard players having just mastered analogue sound creation are now being asked to come to terms with a completely different method of playing and programming. One common belief is that it's impossible to create a new sound without some kind of computer analysis of the original, but fear not; it's all much simpler and more logical than it seems, and with the potted explanation of FM above and the following fine details it should be possible to program a DX7 to sound like a didgeridoo in a darkened room with one hand tied behind your back.
Yamaha's Martin Tennant gives a guided tour of the DX7's membrane-switch control panel which dispels most of the remaining difficulties. The top row of switches above the 5-octave plastic weighted keyboard are devoted to system control, and the bottom 16 to modulation. Once a parameter has been selected it is adjusted with a single left-hand Data Entry slider, which has fine control Plus and Minus buttons next to it. The remaining buttons are for editing sounds and for controlling the cartridge, which carries alternative sounds and slots into the right-hand side of the machine. The cartridge system is far superior to cassette dump because it is instantaneous, and individual sounds can quickly and easily be moved about in memory. The disadvantage is that cartridges will cost about £36. The remaining features of the top panel are the Master Volume slider, the sprung Pitchbend and Modulation wheels, and the central LCD display. This display informs the user which programme number has been selected, the name of the programme, which parameters are being altered, the amount of alteration, battery status and various other useful facts.
The controls are roughly as follows, remembering that each one has a different resolution or possible number of settings on the Data Entry slider. 1—Tune. 2—Poly/Mono, with two versions of each with different release characteristics. 3—Pitch Bend maximum. 4—Pitch Bend stepped (chromatically), or smooth. This control only has two possible positions, as do several others. 5—Portamento Mode (four choices with different release characteristics). 6—Glissando select (stepped portamento). 7—gliss/port time. 8—MIDI bus control, switching various functions to the MIDI output. 9—Edit Recall, will store the last edit change even after the machine has been switched off. 10—Voice Initialise, into a 'default mode' with standard settings from which to create a new sound. 11, 12, 13, not used, as the idea of setting a 'secret code' on cartridges has been abandoned. 14—Battery Check. 15, 16, Load and Save to cartridge. A cartridge protected with its built-in switch cannot be erased.
The lower 16 controls, as mentioned, control the modulation functions. These include depth parameters for the Modulation wheel, the optional foot controller, and the Breath Controller first seen on the CS-01. This can be used to bring in completely different effects under a basic sound, such as brass under a piano chord. The sensitivity of the Keyboard Touch Modulation is also controlled on the bottom row.
One of the separate group of switches to the left, Operator Select, activates an alternative set of functions concerned with the Operators, the Envelope Generators, the Keyboard Scaling and the LFOs. Individual operators can be switched on or off and can have a complex 8-part envelope assigned to them which can be copied to other operators if all the envelopes need to be identical. Keyboard Scaling is the method of producing different sounds at the top and bottom of the keyboard.
Creating a new sound can be time-consuming, but it's not too difficult if an existing voice is used as a starting point. The DX7 is unique in its ability to create more than one sound on the keyboard with each shading into the next, and one preset has a very good representation of a steam engine complete with bell, steam and whistle!
The DX1 may be available by Christmas and will offer more memories, more algorithms and a more comprehensive RAM dump facility. The smaller DX9 is already available, and although it has fewer options than the DX7, a slower tape dump system and no touch sensitivity it comes in a lot cheaper (£899 as opposed to £1299 plus pedals and switches) and can produce many of the same acoustic-like sounds.
Yamaha are following up the inclusion of a MIDI on the DX machines with a computer link and MIDI sequencer, so it's obvious that this is only the start of the FM revolution. It takes a few weeks to get into the DX system, but those lucky few who've had a chance to do so swear that it's worth the effort. Whether DX-type keyboards will ever replace the often heavier-sounding analogue designs is open to question, and for a time it's possible that those who can afford it will want a DX as well as their Prophet or Juno, and not instead of. Only time will tell, but when the mew Yamahas hit the market in quantity it's going to tell pretty quickly.
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Review by Mark Jenkins