FIRSTLY, the price at the top of the page is no joke. Yamaha's new FM synthesiser — which effectively encapsulates two DX9s, a chorus unit, a MIDI switching unit and half a DX7 in one box — will set you back less than seven hundred pounds.

Secondly, it will be in the shops almost as you read these words of wisdom — no lengthy waits to wrap your eyes, let alone your digits, around one.

And thirdly, you're wasting your time looking for a list of compromises such as those which characterised the DX9. The DX21 has hardly any.

Well, a few compromises. But we'll get on to the fine detail shortly.

This is going to be a very important synth, a big seller, so let's do something special for it. Let's pretend that Dr Robert Moog, the father and grandfather of all conventional synthesisers, never existed (sorry Bob) and that his place was taken by Dr John Chowning, the nice gentleman who gave the world FM. Thus all synthesisers to date have been based on the FM process, with which we're thoroughly familiar (there — that's saved a few thousand words of explanation), and the DX21 is just another semi-pro synth which has squeezed through the OTT letterbox for review.

First thoughts are that for £699 this is going to be an ideal first synth. Maybe not a very first keyboard, but a definite follow-up to a Casio portable or a monophonic synthesiser; £699 is cheap considering the facilities the DX21 offers, and what with all the flexible friends being handed out these days, the synth lies in an accessible price bracket.

Second thoughts are that it's nice and compact, although its all-metal casing still gives it a healthy weight which, however, doesn't strain a decent flight bag designed for one hand too much. Taking into account the state of my musculature at the moment, this means that experienced roadies could probably carry two under each arm and another one in the teeth.

Size savings have largely been achieved by removing the pitchbend and modulation wheels from their time-honoured position to the left of the keyboard and putting them on the left of the control panel (à la Moog Rogue or Bit One). This probably saves a lot of money — one circuit board fewer to assemble — and I didn't find it a problem in playing. Some people might. The profile of the synth is almost flat, so there's no chance of contracting OSCaritis (battered fingertips caused by repeated impact on large rubber end cheeks).

The DX21 has five octaves of full-sized keys; to the right of the performance wheels are three sliders for Volume, Balance and Data Entry. Before we go any further, the big secret. The DX21 is eight-note polyphonic in Single mode but can produce two sounds simultaneously in Split mode (up to four notes on each side of a programmable keyboard split) or Dual mode (a slightly limiting four-note polyphony with two different programs sounding simultaneously).

Basically, the voicing is identical to the DX9, with four FM operators available to give sounds with plenty of detail and life. Additionally there's a chorus unit with a simple on/off option, accessed through the function mode which we'll examine in a moment.

The memory facilities on the DX21 are, to say the least, different. It has 32 RAM memories which you can edit, restore and dump to tape (there's no cartridge port). You get at these memories with 32 green switches arranged in two banks of 16 marked A and B; these aren't the slightly over-subtle membrane switches of the DX7 and DX9, but rather pleasant low-profile pushswitches with a small but definite click action — an enormous improvement on the earlier DX switches.

Of course, the memory switches each have some alternative functions, and these are accessed with the function (brown) or Edit (purple) switches. Functions include: master tune; detune for the Dual mode; MIDI send and receive channel (independently programmable); MIDI data content; voice transfer; and performance parameters such as pitchbend and modulation depth, breath control sensitivity, and so on.

There's a lot to go through in the function mode, so let's take it a bit at a time. The MIDI spec is increased over that of the DX7 and DX9: you can transmit on any channel and receive on any channel or all channels (Omni mode). Key information is always sent when the MIDI port is enabled, but you can choose whether or not the DX21 responds to patch changes, key velocity, modulation, breath control, portamento and data entry from outside. The fact that the DX21 can respond to key velocity from outside is a massive advantage; it makes the synth ideal as an expander for a DX7 or for a MIDI sequencer which is being programmed by another velocity-sensitive keyboard.

On to the Edit parameters. As on the earlier models, you can actually alter the sounds by giving different frequencies to each FM oscillator by arranging them in different patterns (the eight Algorithms displayed at the top of the panel), controlling their pitches, and deciding the overall volume envelope with eight-stage envelope generators. One improvement is the fact that once you've selected a facility such as the chorus, you can toggle it on or off by pressing the chorus button; you don't have to return to the data entry controls (although you can if you want to). Parameters with variable values step upwards if you push them repeatedly; this saving of one keystroke may not seem very significant, but every little helps in the light of the complexity of the DX designs.

Other improvements. The LCD display has additional functions marked around the outside so some of its modes aren't quite so obscure. For instance, there's a pitchbend Mode select function which can go to Hi (only the top note held bends), Lo (bottom note) or K On (all notes held bend). The simple fact that these parameters are marked Pitch Bend next to the display is a great help.

So as far as the sounds are concerned, the editing is fractionally easier than on earlier DX keyboards, but there's no major difference from DX9 sounds apart from the chorus, dual mode detuning, and the ability to control by velocity from outside. There is one major advance, though. The so-called Performance Parameters (mono/poly mode, portamento, breath control response etc) are all programmable as part of every patch, as opposed to the earlier models' single performance memory. Pressing Function and Edit together gets into Performance Memory mode, and you simply have to set up one sound or a pair of sounds and save everything to have all your patch information, key split mode, dual mode detuning, pitchbend mode and so on stored together.

This means that your String Bass is automatically monophonic and has Fingered portamento, sliding the note all over the place only if another key is already held down, while your Breath Control Brass already has a good level of response set, and your split Electric Piano/Schmooh patch has a good level of whang to it.

So what's a Schmooh? In fact it's one of the 128 ROM sounds hidden beneath the DX21's RAM sounds. The ROM sounds can be called up at any time in groups of eight — eight Pianos, say, or eight Strings, or eight Basses. They can replace the ROM sounds in four banks; 1-8, 9-16, 17-24, or 25-32. You have to make sure you have any RAM sounds you want saved on tape before overwriting them — the Group-to-Bank procedure takes a few seconds, but at least gives you a fine selection of sounds and some good effects including diesel, Hole In One (for golfers), Zing Plop (name invented by Paul Morley) and three basic synth waveshapes, Square, Pulse and Sawtooth, as well as White Noise.

As for the other sounds, you'll find imitations of a brand new Fender Rhodes piano and an old knackered Fender Rhodes piano; various Hammond organs; lots of brass, including some very sharp and bright effects; various plucked sounds such as folk guitar, kotos, and basses; plenty of eerie sound effects; lots of clavinets and other keyboard sounds; and the usual novelties such as Pan Flute, Rubber Band and Sample&Hold.

The DX21 doesn't skimp at all on external controls. The back panel has stereo outputs, sockets for a portamento and sustain footswitch, volume pedal and tape dump to MSX-style or standard cassette player, MIDI In, Out and Thru, breath controller and headphones. If your knowledge of different keys isn't up to scratch you can transpose the whole keyboard by any amount. As before, patches (and now performance memories as well) can be named by allowing the 32 main switches to double as alphanumeric selectors, and all changes can be compared with the original using the Edit/Compare function. There's a small improvement here as well: the LCD display flashes up a little "e" when you've altered a sound in any way.

The DX21 comes with two manuals — an Owner's manual and a Play Book.

Criticisms of the DX21? Difficult. In fact it's astonishing to see what Yamaha have squeezed into the package. Whereas the DX9 could be described by the things that were missing from the DX7 (no velocity sensitivity, no fifth and sixth operators, no cartridge loading), the DX21 combines some of the same budgetary compromises with a host of plus points which aren't available on the DX7. Result — massive sales, not only (as we mentioned) to those of us moving up from a Casio portable or a monophonic synth to our first semi-pro machine, but also to the professionals and multikeyboardists amongst us who are looking for more FM sounds, a pair of inexpensive expanders which will respond to velocity information, or a high-quality keyboard which will dump sounds to tape rather than the expensive DX RAM cartridges.

The DX21's trick lies in the fact that, while acting as all things to all players, it hasn't fallen into the trap of being a jack of all trades and a master of none (that's enough homilies — Ed). It's almost impossible to fault the machine, even though I formed most of my opinions about it under the delusion that it was going to cost around £900. At £700, the DX21 is mega-biggie.

YAMAHA DX21 FM synth: £699

Contact: Yamaha Musical Instruments, (Contact Details).