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What It All Means


This month we make sense of effects units and what the words say.

'It' being the manufacturer's spec sheet. What good are all those figures if you don't know what the words mean. This month MAKING MUSIC's regular dictionary of terms looks at...


ADA: (see digital delays). The analogue/digital/analogue convertor is the lump that takes your input, converts it to numbers the memory can store, then reconverts it to an output signal your amp can understand.

ALIASING: (see analogue delays). When an echo unit grabs part of the signal in order to delay it, it needs a clock oscillator to say when to release that piece and take in the next one. Sometimes the frequencies of the signal will be faster than the frequency of the clock - a bit like the BBC western where the wheels of the stagecoach turn round faster than the film in the camera. This is aliasing, and will produce unwanted twittering noises in effects, and backwards running Indians on BBC. For flangers and choruses, a filter at the front will take out the dangerous frequencies, and a filter at the back should extract the high whistle the clock itself can sometimes generate.

ANALOGUE DELAY: The old kind which uses the delightfully named Bucket Brigade Device. The signal (voltage) you put in is stored as a charge in a capacitor, which, once full, empties itself into another capacitor, which once full... and so on. It's like transferring a gallon of water along a chain of one gallon buckets. All this filling and emptying takes time, so the signal is delayed from reaching the output, and you get your echo. In real life some of the water would be slopped during the transfer, and so is the signal. It's usually the treble that gets spilt.

BATTERY ELIMINATOR: another name for an external power supply, most often giving you 9VDC from a 250V mains. Once plugged in, it disconnects the unit's on board battery.

CHORUS: (see flanging) another sound that devolves from using varying times - a few milliseconds longer than those for flanging (5 to 15ms, that's why flangers often double up the jobs they do). Imitates multiple voices.

A slap back echo would give you a second 'voice' from the original, but always the same split second later. In real life two people singing the same line would sometimes be spot on, sometimes 5ms apart and sometimes 10ms. That's how the varying delay of chorus adds realism to the effect.

DIGITAL DELAY: The new kind. The signal arrives and is immediately broken down into digital information, essentially being stored as a series of numbers in memory. The memory counts to itself, then, when the echo should come round, simply spits out the numbers and reassembles the sound. Digital delays have their own problems, but produce clearer results because the signals are not passed around so cavalierly.

DRY: dry is the original signal without any effect. If there were a wet bit, it would be the delay, fuzz, flange, etc without any of the original. You mix the two to give the sound you want.

DYNAMIC RANGE: the amount of room you have between your signal being lost amidst all the background noise at the low end, and shoving the circuit into distortion at the other end... headroom. The larger the figure, the better.

EIN: Equivalent Input Noise. Noise figures are easier to measure at the outputs of effects though the noise itself might occur at the input. If you take into account the amount of amplification between the two, you can work out the equivalent amount of noise you're getting at the input.

FEEDBACK: (see flangers) controls the amount of effected signal circled back to mix with the original.

FET: Field Effect Transistor. A breed of transistor much favoured because it uses little power and is quiet. FET switching won't produce an electrical click.

FLANGING: is produced using short delay times (1 to 10ms) that are varied from minimum to maximum by an LFO. When added to the original, unaffected signal these constant changes causes some frequencies to be cancelled out. The effect is that of a comb filter - as its name implies, the 'teeth' of the comb rake across certain frequencies. Flanging is different from phasing in that the notches (cancelled frequencies) are harmonically related - odds cancel and evens reinforce. A more distinctive sound, therefore. The title 'flanging' (legend has it) comes from studio engineers who produced the effect by playing identical tapes on two recorders in tandem and slowing one down by pressing on the flange (outside rim) of the supply reel. Silly boys.

INPUT IMPEDANCE: a measure of the 'resistance' a circuit will put up to an incoming signal. Unlike resistance proper, it will vary with the frequency of the signal. The higher the figure, the better, but you should ensure that for the best matching, the input impedance of your effect is higher than the output impedance of your instrument, mike, etc, otherwise you might begin to notice bass loss.

LCD: Liquid Crystal Display. A thin layer of this crystal will turn opaque when a low voltage is applied. Lay it down in the right shape (like a number) apply the volts, and you've got your readout, providing there's a reasonable light falling on it.

LFO: low frequency oscillator. The slow running part of a circuit that will cycle round the delay times in choruses and flangers, change the volume in tremolos, the pitch in vibratos, etc, etc, etc.

MINI-JACK: small version of the standard ¼in thick jack plug, often used (in plug or socket form) to connect external power supplies to effects pedals.

NOISE GATE: listens to your signal and when there's nothing there (you've stopped playing) turns off the effects output so you can't hear the background hiss and noise. Some will be adjustable so they won't mistake your very quiet playing or gradual fades for silence and chop them off as well.

PCM: Pulse Code Modulation. A system of sampling and storing sounds. Technically, the waveform to be sampled is converted into a series of binary codes by taking many, very fast, repeated measurements of its amplitude.

PHASE REVERSAL: often seen on reverbs or echoes, and is held by many to lend a greater realism and 'openness' to the final sound. We won't delve too deeply into the pyscho-acoustic reasons for this, but we concocted the following explanation, which nobody seemed capable of disagreeing with. Imagine you're in a room with sound bouncing back at you off the walls (otherwise known as reverb). The chances of these signals arriving at your ears exactly in phase with the originals are very slim. More likely, in the real world, that they'll be out of phase.

ROLL OFF: how frequencies fall off in level. Eg a bass roll off means the bass will decrease past this point.

THD: Total Harmonic Distortion (an old friend from last month; new readers start here) unwanted signals harmonically related to the input, and not just rlan'Sdom (sorry, random) noise. The 7th, 8th and 9th harmonics are where it begins to get unpleasant, but measuring devices can't easily separate the harmonics so that's why you get the total. Ideally, spec should specify THD across the entire frequency range as it can vary.

12BIT/14BIT: if you like, the power of the chip that samples your sound. The higher the figure, the better (in general) the quality.

UNITY GAIN: an amplification factor of nothing, squire. You get out what you put in.

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Making Music - Copyright: Track Record Publishing Ltd, Nexus Media Ltd.


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