Effects and Signal Processors - Distorsor

It is not a distortion of the truth (excuse the shakespearian pun..!) to state that this effect has literally changed music history. The birth of rock music in fact owes a lot to this effect, which was discovered by chance as a result of a wrong amplification. The functioning principle of the distorsor is very simple. When the amplitude of a signal goes beyond the maximum threshold-level at an amplifier's input, a phenomenon called saturation takes place. This means that when the input-signal is lower than this threshold, the amplifier works correctly and at output it reproduces an amplified wave-form. However, when the input signal goes beyond the threshold, the amplifier has, indeed, reached its threshold, and thus cannot further amplify the wave-form. This in practice means constant output at the amplifier's threshold-point during the time-span in which the input signal remains above this threshold-point. When the input signal comes back below the amplifier's threshold-point, the amplifier begins to work properly again. The following diagram illustrates the amplifying-curve of an amplifier, and its action on a sinusoidal input signal whose maximum levels surpass the amplifier's threshold-point.

Effects of the saturation of a sinusoid

So, at the output we have a "saturated" signal. Saturation introduces a sudden variation of the signal, which no longer follows its natural sinusoidal behaviour, which in turn means that the new signal contains new frequencies which are higher than the original ones. Let's now explore this fact from a signal-theory perspective, by referring to the notions we introduced in its pertaining section [Distortion by saturation ] .

We have often spoken about how any complex signal can be recognized in sums of sinusoids at different frequencies (and phases). The more sudden the transitions presented by the signal, the more frequencies are necessary to reproduce it in terms of sinusoids. If we take a look at the saturated sinusoid in the diagram, we can see that some very sudden transitions have been introduced into it and there must therefore have been an addition of new frequencies to the spectrum. It is these new frequencies that generate the typical sound of distortion. So, distortion at its purest is obtained by lifting the gain level of a pre-amplifier in such a way that part of the signal which will then reach the final amplifier [Amplification curve ] . can go beyond its threshold-value. A good Marshall valvular amplifier generates a marvellous distortion sound. If you don't have one, you can use an effect which simulates saturation, even though, clearly, the quality of the effect won't be quite the same.

The following is an example of a sound to which various distortion effects have been applied.

Table 7.3. Distorsor 

AC30 Crunch Light [Track 32] Marshall Heavy [Track 33] Mesa [Track 34]