With the release of the RX21, Yamaha aim to take the lead in the affordable drum machine stakes. But have inevitable economies resulted in an instrument that's worth taking seriously?

One of the strengths of digital technology is that it keeps getting cheaper and cheaper. And for today's musicians, this can only mean that the instruments they buy that make extensive use of this technology (synths, samplers, drum machines, sequencers and now the new generation of digital signal processors) are going to go on getting cheaper as well - and at a rate which wouldn't have been dreamed of even three years ago.

Yamaha's latest drum machine, the RX21, is a case in point. At all but £250, you can now get what amounts to a professional drum machine at less than a semi-pro price. Inevitably, there have been compromises at the design stage in order to get the price down this low - but not as many as you might at first suppose.

First, to the drum voices themselves. You'll not be surprised to learn that the RX21 follows the Japanese drum machine tradition of presenting a closed system when it comes to voicing - that is, it offers none of the expansion possibilities the Americans are so fond of (the Sequential TOM's plug-in cartridges, for instance). I guess that in these days of MIDI modularity, it could be argued that the production of cheaper units the musician can add together as finances permit is a better route to take, but it's by no means a one-sided argument.

So what you get here are nine PCM-encoded voices comprising the familiar kit sounds, plus the ubiquitous handclaps. A year or two back that would have seemed a decent enough selection, but now that Roland and Korg have started freeing impecunious musicians from the restrictions of kit drums, it might have been wise for Yamaha to follow suit. It remains to be seen whether an 'RX21 Latin' is on the stocks.

In case you might be thinking that the RX21's budget price has resulted in a lowering in quality of the voices, I should stress they're actually the some sounds used by the company's RX15 drum machine - it's just that there are fewer of them. And if there's one thing that characterises all these sounds - bass, snare, three toms, open and closed hi-hats, crash cymbal and handclaps - it's presence. They're all crisp and punchy, with the bass drum and low tom in particular having plenty of 'oomph' behind them. No danger of any of these sounds getting lost in a mix, I'd say. If it's blitzkreig attacks on the sensibilities that you're after, you'll be happy to know that the 21 is capable of playing all its nine voices at once... well, almost: Yamaha have bowed to tradition in not allowing the open and closed hi-hats to sound on the same beat..

Along with the overall volume level, it's possible to set individual levels for each voice, though these levels aren't programmable per pattern - more evidence of cost-cutting by comparison with the RX15, on which they are.

What has been retained from Yamaha's more expensive machines is the more useful facility of being able to program an accent for any voice on any beat. Thus you can reinforce a four-to-the-bar (or the downbeat on some odd time signature like 7/16), turn a beat around, or give some sizzling syncopations some extra bottle. Accentuation is also useful for giving added interest to sustained cymbal sounds that are being played repeatedly - on the RX21, it's particularly effective applied to the open hi-hat. The problems start when you realise that the 21's accent is programmable for each step, rather than for each voice. So if you have two voices playing on the same step and you want to accent one of them, the other will be accented as well. You can vary the amount of accentuation you give to each voice (though again, this is not pattern-programmable), but it's still not an ideal situation.

So much for the voices. What of the RX21's memory capabilities? At first sight the RX21's budget price doesn't seem to have affected its provision of patterns: a creditable 100. However, it transpires that 44 of these are preset rhythms, safely tucked away on ROM so that you can't get rid of them. This still leaves you with as many programmable patterns as you get on Roland's TR707, but the patterns Yamaha have provided on ROM are neither as varied nor as interesting as they could have been, and I kept finding myself wanting to get in there and muck about with them.

Talking of changing things a bit brings us on to the actual operation of the RX21. Patterns can be recorded in real and step time and freely passed between one mode and the other. Thus you can record some parts of a pattern in step time and some in real time, or perform step-time edits on parts recorded in real time — a nice degree of flexibility that's made possible by the fact that all input, whether in real or step time, is quantised to one of four values (only one of which can be active per pattern, of course). These are 12, 16, 24 and 32 (ie. triplet quavers, semiquavers, triplet semiquavers and demisemiquavers). And you'd better decide whether you want triplet or 'straight' type quantisation before you start recording, because you can't change from one to the other once finger has been laid on pad. More of an irritation than a limitation, though.

The maximum length for a single pattern is 16/16, and this can be reduced to as little as 1/16. Real-time recording gives you the usual metronome beat on each crotchet, accented on the first beat of the bar. In time-honoured fashion, the pattern loops continuously until you exit record mode, so that you can add to it at whatever point and time you want. Any beat you don't like can be deleted by judicious application of the Clear button in conjunction with the appropriate voice pad, though if that beat is also an accent, you need to find a third finger for the Accent pad.

The 21's version of step-time writing allows you to enter one voice at a time on each quantisation step (rests are input by means of the all-purpose '+' key). As with real-time recording, the steps keep looping until you exit record mode, so you can build up your pattern gradually. As you move through each step, the voices already recorded on that step are played back to you - if only every step-time system did that. And as I mentioned earlier, you can move to real-time writing at any time and carry on recording your pattern, should you wish.

"Sounds - They're actually the same voices used by Yamaha's own RX15 machine — it's just that there are fewer of them."

But Yamaha have done a bit more with the step-time system. Specifically, you can view a step-time representation of your patterns (one voice at a time, of course) in the LCD window, where a system of dashes and dots gives a clear indication of each step while small blobs (they look a bit like hand grenades) show where a beat has been placed. Not even Yamaha's costliest digital drum package, the RX11, has a visual display of this kind, and it's certainly a useful inclusion that's as educational as it is informative. In fact, my only major grouse is that, like so many LCDs, this one isn't backlit, so that unless you look at it straight on in decent light, you have to use it 'at a stare' rather than 'at a glance'.

Like any decent programmable drum machine, the RX21 allows you to combine patterns into songs. In all, the memory can hold four of these songs, each of which can be made up of as many as 512 patterns. My own feeling is that more songs with fewer steps would have been far more useful, both for live work per se and for using the RX21 in conjunction with a MIDI sequencer. To give the memory eight songs of 256 steps each, or even 16 songs of 128, would surely have cost very little extra in software terms.

In song mode, the RX21 gives you the basic editing facilities of inserting and deleting steps, but what you won't find are any of those useful facilities that give you real flexibility in song programming, such as tempo changes and pattern repeats. Again, you have to look to a more expensive instrument such as the RX15 for features like these.

On a more positive note, one area where Yamaha deserve much praise is in front panel design. Not for the rubber buttons and pads that they've endowed the 21 with (the triggering pads are OK, but the control buttons are a bit on the dinky side), but for the ease with which it's possible to find your way around the instrument. For any newcomers to the world of drum machines, the RX21 shouldn't foster any phobias - the control layout makes it a doddle to use, even if the scaled-down facilities must also be partly responsible for this.

As on the RX15 and RX11, Yamaha have provided a facility for copying a pattern from one position into another - useful if you want to take a pattern and adjust it bit by bit for inclusion in a song, for instance - and you can clear both patterns and songs at a touch of the appropriate button. There's also a Repeat on/off function which affects patterns and songs alike, while tempo is continuously variable from crotchet=40 to crotchet=250.

When it comes to conversing with the outside world, the RX21 is strictly MIDI-only, with one each of MIDI In and Out sockets on its rear panel. The machine can be set to read either its own internal clock or incoming MIDI timing bytes, allowing the RX21 to control or be controlled by a sequencer or another drum machine.

And yes, you can play the 21's voices from a MIDI keyboard, though not vice versa, it seems. The MIDI receive channel for this purpose can be any one of the 16, which gives you maximum flexibility if you want to run the RX21 off a MIDI sequencer. However, voice-to-pitch allocation is fixed and you can't actually record patterns into the RX21 from a remote source. What this facility is rather handy for, though, is playing the drum machine voices from a MIDI keyboard or sequencer without regard for how the RX21's internal configuration puts together its rhythms.

It'll come as no surprise to all but the inveterate dreamers among you that audio output on the RX21 is confined to left/mono and right outputs (and headphones, of course). For the delights of individual audio outs, your cheapest bet is still Roland's TR707 or its Latin percussion equivalent, the TR727 - but just remember the RX21 is half the price of either of these. There may well come a time when affordable multitrack facilities make individual outs de rigeur on all drum machines, but in the meantime, there's no reason why the average Portastudio owner on the lookout for an affordable drum machine shouldn't be fairly content with stereo outs, whilst perhaps wishing Yamaha had included user control over stereo panning of the RX21's voices.

"Programming - To have more songs with fewer steps would have been a lot more useful, both for live work and for running with a MIDI sequencer."

External storage of the 21's data can be to either cassette (with the familiar array of save, load and verify functions - a complete dump takes 15 seconds) or via System Exclusive MIDI dump (though this, of course, requires a computer and appropriate software at the receiving end).

Chances are that if you're prepared to read a review of a drum machine that sells for £250, you're unlikely to dismiss the RX21 out of hand. It certainly offers enough in terms of voice quality, memory and programmability to satisfy a good number of people, and it has to be said that at roughly half the price of any other MIDI drum machine currently on the market, it offers more than half the capability.

The problem lies in the fact that the further down the price scale you go, the smaller price differentials become - so that whereas there's a fair old price difference between the new DX21 polysynth and its illustrious elder, the DX7, the difference between an RX21 and an RX15 is rather less. Thus it may be that a lot of musicians will pass over the 21 in favour of its more facility-laden colleagues, spending more money but getting a more expensively specified instrument in the process.

On the other hand, the idea of a MIDI drum-and-sequencer combination for around £500 (something the RX21 and the Casio SZ1 sequencer, reviewed elsewhere this issue by yours truly, make possible) is certainly an appealing one. Neither machine is the pinnacle of achievement in its marketplace, but both make a lot of economic sense.

The RX21 makes musical sense, too. For unlike some budget instruments, it's been designed with care and built to standards that are higher than some machines costing twice as much.