"FB01? WONDERFUL, BUT how can I take it seriously if I can't program it and it doesn't have an X in the name?" You can just imagine the reaction to that in Hamamatsu, the tearing of hair and cursing at the ingratitude of The Great Expander-Buying Public. However, those members of the design team who didn't commit seppuku or take up underwater soot juggling have stuck to it and produced Son of FB01.

Or should it be Distant Cousin? Because the TX81Z is a rather different machine. For sure it is programmable, has eight voices, is multi-timbral and uses FM synthesis with four operators. But eight different waveforms? Programmable program-change table? Programmable microtonal tuning? And all for less than £500? This is Yamaha product development in a feisty mood.

Those extra waveforms allow you to achieve with a single operator what on any other X-series synth could take a two-, three- or four-operator stack. Perhaps more important to all those musicians who have bemoaned the sheer inaccessibility of FM programming, making interesting noises is rather easier.

However, FM remains as non-intuitive as ever, and the TX81Z's user-hostile front-panel (viz. a handful of buttons to access over a hundred parameters) does nothing to help. Still, Yamaha have provided a neat little pull-out card to remind you what all the parameters are, and the sequence in which they appear in the backlit LCD.

Despite the extra waveforms, the sounds are still very FM: clear, sharp brass, splendid pianos and weedy strings, all enhanced by the stereo output. As with the new DX7s, overall sound quality has been improved with better digital-to-analogue converters (so less aliasing and general noisiness) and better resolution on the envelope generators. There's also a "pseudo reverb" which adds a bit of character, and three useful special effects: panning, chords generated from a single note, and transposed delay, all programmable for each voice.

The voices are stored in five banks of 32 voice memory locations. Only one bank is user-programmable, the rest containing the usual assortment of Yamaha presets. Each voice memory location holds a complete set of function data (pitch-bend range, portamento time and so on) to complement the voicing. Unhappily, there is no provision for a cartridge ROM or RAM, so you may find yourself making more use of the presets than you might like.

In multi-timbral mode, each grouping of up to eight voices is referred to as a performance; there are 24 performance memories, all of them programmable. When constructing a new performance, the TX provides four basic settings - single voice, dual, split and eight mono voices - which can be customised to your requirements. Each voice can be assigned to a different MIDI channel, and can occupy the full note range from C2 to G8. Each voice can be shifted by up to two octaves up or down in semitone increments, and can be detuned by up to seven increments either way. The volumes of individual voices can be balanced at the set-up stage, but subsequently overridden by a MIDI volume command. If you want to be deeply bizarre (man), you can assign some voices to one of the available microtonal scales and the rest to equal temperament.

Again, like the DX7IIs, there are 11 built-in microtonal scales and two user-programmable. In creating your own scale, you can either set up a single octave and then transpose it up and down the scale, or you can program every single note with a different interval.

The TX81Z recognises all four MIDI modes, and has a couple of extra goodies built in to make it more flexible: channels can be specifically assigned to receive system exclusive commands and controller commands; and voices and performances can be transmitted over MIDI, either individually or in groups of 32 and 24 respectively. More interestingly, you can transmit and receive all the other system settings, such as the program-change table, the two user-programmable scales and the data for the three special effects.

The program-change table allows you to reassign any incoming program-change command to any individual voice or performance memory. Program changes take a little time, so you need to be careful where you place the change commands in your sequences. Changing from one single voice to another takes about 1/16 second, which is very noticeable if it comes out of the first beat of a bar; changing from one performance to another takes up to 1/8 second. In both cases, anything sounding when the change command arrives is stopped dead, leaving a "hole" in the sound.

The manual is a gem. Each parameter is covered in detail in the same sequence as it would be programmed. There are overviews of MIDI and FM programming, and lots of diagrams and tables to help you find your way around. Yamaha are clearly very interested in getting software developers to create applications for the TX: they provide immense detail on all the system exclusive commands, and the datastreams which the commands create.

The TX81Z is bound to be an immensely popular instrument, that forbiddingly sparse front panel notwithstanding. It combines the power of FM synthesis with a very complete MIDI implementation at a rock-bottom price. What more could you ask for...? No, don't answer that, Hamamatsu already has its fair share of underwater soot jugglers.

Price £449 including VAT

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