Why is a fuzz box? No, not what... "why"? How is it that one arrangement of transistors, wires and batteries can sound like a distorting valve amp, while another ends up as a phaser? You nod wisely to yourself, the cosmic truths finally confronted and explained. Colbert, you say, has gone off his trolley.

Still, we shall persevere with an anatomy of effects pedals, and first under the scalpel is the aforementioned fuzzeroo.

Essentially it's an amplifier that doesn't know its own strength. Supposing it's fed a clear guitar note which, for argument's sake, we'll represent as a smooth, undulating sine wave drawn on a sheet of paper. One half of the circuit tries to boost the signal volume so magnifying that wave, but if the piece of paper remains the same size then the peak won't be able to fit on it. The line will go straight up, along the edge of the sheet then straight down a bit later.

It's now a square wave, more or less, with a completely different character. The harmonics, which determine the quality of any sound, have been rearranged. Of course it can vary in degree (fuzz strength) between just the top of the sine wave being shaved off—often referred to as the "onset of clipping" — or the full waveshape distortion.

Incidentally, square waves are particularly strong in second harmonics, that's the note an octave up from the one you're playing. In many fuzz boxes you can hear that additional note quite clearly.

Fuzzes I've liked recently have been the Guyatone Overdrive and Ibanez Tube Screamer, but you can get similar effects by overdriving the first stage of your amplifier. Many amps even have an extra pre-amp gain control to help you do it.

Valves distort in a different way to transistors (see our valve piece on page 76), but lately there have been developments in MOS-FETs (field effect transistors) which are said to share a similar harmonic profile to the old bottle.

Compressors, on the other hand, are almost fuzz boxes in reverse, they turn down your signal to prevent it overloading. The compressor has a final output level which it has to adhere to. An early section in the circuit senses the new incoming note, realises it's going to be louder than the permitted figure and rapidly dumps the excess.

All this happens so quickly that to your ear the change is instantaneous. All that leaks through of the original overloud input is a split second burst of power heard as percussive click. That's what produces the fierce attack and punch which makes compressors popular.

Badly designed compressors can be heard turning themselves up again ready for the next note. This is a problem created by "slow" circuits and they'll sometimes sound as if they're breathing.

Yamaha are making a versatile gadget at the moment, and the Frontline one is cheap, yet still effective.

It's a different kettle of silicon when we arrive at choruses, flangers and echoes. These are all effects based on delaying the signal — for a long time (at least 100 milliseconds) for echo and a much shorter time (say 3.5 to 14 milliseconds) for the other two.

One way into this maze is to look at automatic double tracking, which is simply the original signal, then that signal repeated once a split second later. The mind hears two identical notes that are far too close to be an echo and presumes there are two instruments playing at the same time. Easily fooled, is the mind.

One electronic method of delaying the signal is called a "bucket brigade". Imagine the incoming note as a gallon of water which fills up the first bucket, that one empties itself into the second pail, the second then disgorges its contents into the third and so on. All this takes time. If you then swap the analogy to a capacitor charging up with a voltage then releasing it, you'll see how the electronic method can work. Capacitors can charge and discharge at lightning speed, so you need a lot of buckets to produce a delay.

To explain the mystery of the chorus unit, you have to consider the psychology of sound a little more. With ADT, the mind decided there were two instruments always playing a few milliseconds out of sync. Supposing you could alter that delay so it was first 4ms then 5ms then 7ms then back to 4ms — maybe the grey cells would reckon there was an entire crowd all bashing away at their gear.

Thus we have a chorus unit. It contains a low frequency oscillator which gradually changes the delay time in a continual sweep. One further mental boost is that two identical instruments side by side will not only be fractionally separated in time but also in pitch. The squeezing and expanding of the delay time results in a small rise and fall in pitch so adding to the chorus effect.

All this goes on around delay times of 5ms to 14ms. Much above and the pitch shift becomes disturbing, much below and you lose the feeling of separation. It's in this lower area that you encounter flanging. The same principles apply, but instead of a movement in time there's a movement in harmonics. As the low frequency oscillator slowly goes through its paces, the original and delayed signals interact, creating the characteristic "sawing" sound. Many flangers that straddle the time barrier also have a chorusy feel to them and there are many pedals on the market that do both jobs, occasionally to the detriment of both.

One other problem you may encounter in cheap effects is the quality of the LFO. Ideally a sine wave oscillator would be best, taking the delay through the smoothest possible journey. Unfortunately it's much easier to build an approximate triangle wave LFO and if this is badly set up, the delay may accelerate to a maximum and rapidly fall away. It's this peaking which creates the lumpiness heard in bad chorus, flanger or even phaser units.

The Boss BF-2 is a powerful flanger, cold in sound perhaps, but unusually quiet and compact, and the similarly priced Ibanez (they're both around £80) is good at its job. Probably champion of the small chorus pedals at the moment is the latest Boss CE-3 which has two stereo modes.

Such a gadget will send the original signal to one speaker and its delayed half to the other. Since we started with a time difference and a pitch difference, that separation in space is the final clinching factor.

By ditching the LFO and greatly increasing the bucket length you arrive at a delay line. When your gallon of water is poured from the last in the chain it may be up to 300ms "late", but that's only one repeat. For real echo it has to be looped back to the beginning of the brigade. The intensity control decides how many times it will make the voyage. It can reach the stage where the signal is doomed to wander the buckets for ever, like a ghostly highwayman galloping the moors until his spirit is laid to rest, or the battery runs out.

I don't want to get too carried away with this bucket comparison, but there's one more useful analogy. Each time the water is moved, a little is spilt or left behind. At the end of a long trip it may be down to seven pints.

In the same way your signal will lose out, invariably in treble. How efficient the transfer is dictates the quality of the final sound. The Boss DM-2 Delay preserves the upper frequencies and supplies unusually long delays in such a small pedal. MXR are also famed for their delays and at a higher price range both the Ibanez DM1000 and Cutec CD-424 are fine value.

It's true that you can get duffers while shopping around for effects — noisy ones, lumpy ones, and so forth — but it's wrong to think there is the ideal for which all flangers and fuzz boxes should strive. They can be as different as guitars or keyboards and it's a matter of listening around until you find one that suits your ears and wallet.