In the world of multitrack recording, Fostex's X-15 recorder is the point where the majority of today's musicians probably start. Tascam's new Porta-1 (see last month's IT review) may well offer more facilities - but it costs more money, and the X-15 still looks attractive by comparison as the natural starting point in a home recording career; either through shortage of money or lack of confidence in being able to operate a bigger machine.

But where do you progress to when you've begun to outgrow the - admittedly rather limited - facilities of the X-15? The natural move might be to sell it to another beginner and look around for a more sophisticated 4-track cassette machine - but do you have to: especially if your wallet remains empty?

One answer could be to expand your X-15 with the ingenious Fostex MN-15 add-on mixer/compressor, with its very affordable RRP of just £45.95 inc. VAT. It could be a much better bet than trading your X-15 in for a bigger machine.

The MN-15 is a small but sturdy, black plastic-clad unit which considerably expands the X-15's abilities. On its own the Fostex recorder has only two inputs and features rather limited facilities for 'ping-pong" overdubs - which is where the MN-15 comes in.

The four fader/slider controlled input channels of the mixer (which is powered by either a single PP3 battery or an optional mains transformer, by the way) are connected to your X-15 via four 'tape in' phonos, along with an extra input channel which enables you to connect either mike or line level signals. This extra input is by either a standard 1/4" jack socket, for mike inputs, or a phono for line level feeds - electronic instruments, other tape recorders and so on. To set the ideal level for the type of input you're planning to use, a 3-position slider lets you choose between 'Mic', 'Att' (attenuated) and 'Line' settings, hence it should handle just about any source you're likely to want to use; 'Mic' and 'Att' selecting the phono input and setting the level for jack inputs, 'Line' connecting the rear-mounted phono socket.

Plugged in and wired up, the MN-15 enables you to take up to three individual tracks from the X-15, blend these with a 'live' overdub and mix them all down (via a single phono output) to one track on the recorder for more complex overdubbing effects than the X-15 alone can achieve. Given the X-15's lack of a noise reduction system, this could result, in theory at least, in annoying hiss levels - were it not for the fact that a built-in compressor is provided on the MN-15 - and (especially considering the price) it's a very effective one. Switchable either in or out, the compressor has a variable effect - a compression ratio of 6:1 being offered with maximum compression of better than 20dB. Attack time is quoted at 0.5mS, release time at 50mS-1 sec, variable - an impressive range on such a small mixer.

The main use of this effect lies either in holding back unwanted 'peaks' when you're mixing down your combined recorded and 'live' takes to a single track. It cuts out distortion from unwanted peaks and also enables you to 'tighten' or add 'punch' to your sound.

The compression effect is certainly versatile enough to allow you to experiment and get a sound suited to your particular needs at the time - and it's an easy one to govern, too, as red and green LEDs show min and max levels.

In practice, how you'd probably employ the compression (the amount of which is controlled by the fader on the 'overdub' input channel) is to set it so that the red LED flashes during peak level inputs from your 'live' signal. Having reached that point, you can then adjust the 'release' time (governed by its own fader) to dictate how fast the compression plays out. How you set release will depend very much on whether you're recording a vocal overdub or one from an instrument - and that's down to taste, trial and error.

Practically, we were extremely impressed by the MN-15's capabilities. The sample unit was well manufactured, the faders travelling nice and smoothly, the whole unit feeling tight and secure. Sound quality too was exceptionally good for the price. The compression effect, for example, operates both smoothly and progressively and adds a definite reduction to the levels of background noise which you'd get without it. It does this, of course, because it enables you to re-record your maximum of three previous tracks plus overdub at the highest possible level, without fear of overloads - thanks to the compressor. Our MN-15 didn't generate any noticeable noises of its own and performed flawlessly on (quite a long) test.

Any reader with a Fostex X-15 who's been considering upgrading to a more complex machine but can't really afford it, or anyone who, perhaps, has been put-off one because of its apparently limited facilities, really must look at the MN-15 before making any sort of decision. It works very well indeed - expanding the X-15's capabilities quite considerably. At the low RRP it seems to us like an exceptionally good buy.

Just one small criticism did occur to us, however. A lot of the owners and prospective buyers of both the X-15 and the MN-15 will be very unsure of themselves in terms of both recording terminology and practice. We felt that the MN-15 deserved a more detailed explanation than that offered on the double sided A4 sheet which came with it. A clearer explanation of what it does - certainly more about how to use it would really assist owners and potential buyers, and this is something which, possibly, either Fostex or Bandive (their U.K. importers) could have a look at. A bargain, nonetheless.

RRP £45.95 INC. VAT

More details from Bandive Ltd, (Contact Details).