Dimension C? Isn't that where Doctor Who occasionally goes after being zapped by one of his scaly interplanetary foes? Or maybe it's a technical drawing term? Or a new wonder drug? Or... no, wrong in each case.

According to Roland, it's a "compact version of the Dimension D; a rack type unit that creates an excellent chorus effect". So now you know. Lookwise, it's in the standard Boss footpedal box, with precious little in the way of knobs, sliders and dials — just four small silver buttons and an LED to indicate battery status.

Oh, and one last thing, before you rush out and compliment Roland on their tasteful simplicity. It's the colour of a Ribena bottle, a sort of violet hue that went beautifully with my green Portastudio and yellow guitar. The dog was sick almost instantly.

As for the sound, it's unlikely to evoke such strong reactions. It's pretty subtle, and with only four 'modes' to choose from there's nothing you can fiddle with to bring the effect into the realms of over-the-topness. Not the most psychedelic of things, then.

So what does it do? Through one amp, in mono, it gives the sound an edgy, chorussy chime which does more or less what a chorus pedal would but without the churning, cyclical sweep that runs through a chorussed sound.

In stereo, it really opens up the sound of the instrument but again without that side-to-side seasickness that chorus brings. It's a wide, spacious and full sound that comes out, broadening the stereo image without any real spatial movement (man).

But it's when you plug the doobrie into a recording device of some kind that it comes completely into its own. It makes the noise you always hoped a chorus would, but without the irritating boingy swirl that sounds so horrible when it gets out of time with a track. It simply puts the instrument into a very clean (it has built-in noise reduction circuitry) very glossy wrapping, giving your tatty Strat copy the mistaken idea that it's a vintage Fender being played by a top LA sessionman. On keyboards, it gives string sounds a lush presence and brings tinkly synth or piano lines into sparkly close-up. Lovely. Even vocals could benefit from a touch to give them a zingy, spacey and slightly double-tracked effect.

It's very nice, in other words. I wouldn't complain if Roland gave me one. But at One hundred and thirty greenies they're hardly giving them away. It's a lot of money for so subtle and, let's face it, so inflexible a pedal. You get a choice of four modes of slightly different delay times and degrees of subtlety, but that's all you get. No finer adjustment, no facility to create your own personal settings or adjust mid-set if it's too much one way or the other.

It boils down to the value you place on that 'big' sound; Pat Metheny fans (come on, I know you're out there) will love it, and devotees of that smug, fat, LA guitar sound could put it through a compressor and maybe add a touch of overdrive to achieve the guitar sound of their dreams.

Keyboard players may find it rescues their muddy presets from the doldrums, and even solo acoustic guitarists might like it for the way it gives depth without obliterating the natural sound in a welter of up-and-down modulation.

But even so it'll have to be a well-heeled musician that forks out £130 on a pedal that adds so subtle a refinement to their sound. It gives you a big, expensive sound. But it should do, because it is expensive. You battle it out with your bank.

Robbie Blunt (Robert Plant band): "I only use one effect as a rule — that's the Roland Dimension D, which is a rackmounted effect. I use it with two Mesa Boogies and it makes the guitar sound clean but glassy and it's stereo."

As for the Hi Band Flanger, it isn't particularly pricey. These days £89 isn't a huge pile to part with for a good quality, versatile flanger (I remember the days when you could get four Cry Baby wah-wahs and still have change from a farthing, mumble mumble... ) and there's no doubt that this is one of the best I've tried.

The reason it's called a 'Hi band' flanger — and not, for instance, an 'Ironing Board' or a 'Guacamole Dip' Flanger — is that it apparently yields a flanging effect "at one oct up than in conventional flangers". Roland's obviously hardworking translation department also say "The new circuitry sounds more clearly and briskly", which is certainly true.

Whatever the reasons for its different sound, this unit definitely does have a much more toppy, resonant edge to its sound than most others, which in contrast sound like they're stirring porridge. The flipside of this is that it's very easy to go overboard on the flanging effect and sound like a succession of F1-11 fighter planes passing overhead at low altitude. Whooshes a-go-go, if you're not careful.

Turned to a minimum setting, the pedal gives a clean, clear chorus in the classic style, and when you start to wind it up you can get virtually every sound in the flanging repertoire from the sweeping pseudo-phasing stuff to the wobbly space-age and well beyond into areas where only an acid-crazed chimpanzee would attempt to use the resultant effects.

A good pedal, though to take the flanging idea much further it would have been nice to have had stereo outputs. Surely it wouldn't have cost much more, either. Maybe next year's idea? But for a mono flanger, Boss have gone at least one step beyond anybody else's efforts. You may find you still prefer the more 'traditional' type of effect, though, so it's worthwhile testing an old-style one side-by-side with it.

Oh, and it's an even more psychedelic colour than the Dimension C — sort of cerise pink. Next — the first green-and-orange Paisley overdrive unit?

One expensive success, one well-priced well-built improvement on a tried and tested principle. Boss haven't lost their knack for good sounding, soundly constructed effects, but these two seem to be more treading water than really breaking new ground. Maybe a cheap Dimension C (Dimension B?) or a stereo flanger would have been more of a boon to the starving masses than these two, pleasant though they are.

Except for the colours.

Dimension C pedal: £130
Hi Band Flanger pedal: £89