About Saturation

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Saturation is a key effect in rock music. People started using it in the early sixties, by means that had very little chance to give an interesting musical result: push the amps beyond their nominal limits. Well, it worked, so let’s forget history, and focus on facts.

Saturation is only one of the many distortions that can occur in an audio set-up. As a matter of fact, distortion applies to any process which is not strictly faithful to the original signal. With this audiophile definition, every instrumental piece of gear is a source of distortion.

Saturation refers to pushing a device beyond its normal limits: a speaker can be saturated (mechanical saturation - it doesn’t last long), the output transformer of a tube amp can saturate (that’s magnetic saturation), and of course, all the active components of an electronic circuit can saturate (the passive components can burn out, but do not saturate).

Saturating active components causes signal clipping. These components have, by definition, a power supply that can provide a limited amount of energy. Ask more energy, and it won’t respond: the signal is clipped. That’s what happens in an overdriven tube amp.

An overdriven solid-state circuit (transistors, FET’s, OpAmps, etc…) can give similar results, and can be used to obtain the same sound as a tube amp – provided you can control the result with the proper filters.

Clipping can also be obtained without active saturation: you can use diods to achieve clipping, because their natural behavior is to clip one half of the signal. Diods are actually in-between components based on the same technology as transistors, but they are used as passive components.

That’s a brief recall about saturation and its objective: clipping. We want to clip the signal to obtain a sound that has some musical qualities.

Oh, I was forgetting something critical about saturation and clipping: they don’t only alter the dynamics of the original signal. They just suppress it! In other terms, a saturated signal has the same dynamics than a hyper-compressed signal – though the principle is totally different.

So what? Losing the dynamics makes a guitar sound absolutely different, as if it was another instrument. And that’s what makes it attractive for rock music: this new instrument – saturated guitar – has its own identity, its own culture, and even allowed creating new styles of music: hard rock, metal rock, heavy metal, arena rock, wouldn’t exist without saturation, or should we say, clipping.

So, what does clipping, exactly? Clipping does two things:

  1. Saturation and clipping suppress the dynamics of the signal: the amplitude variations (the envelope) are erased, gently first, then strongly if you increase the input signal level (that’s the “gain” pot).
  2. Clipping adds artificial harmonics. The more you saturate, the more harmonics you get.

Great, but we already had natural harmonics, hadn’t we? Yes, we had, and they are still here. So a saturated guitar signal is made both of natural harmonics and artificial harmonics… Merging the two families (artificial and natural) of harmonics (they all have the same frequencies) will cause complex inter-modulation effects. Some interactions are pleasant to the ear, and some are not. Moreover, the possible number of combinations is simply huge – and this explains why there are so many types of saturations, distortions, fuzzboxes, overdrives, etc…

All these effects are based on the same structure. All. They just differ by the filters placed before the clipping stage, that control the input signal harmonics distribution, and the filters placed after the clipping stage, that control the result – natural and artificial harmonics. You can of course, make things more complex by placing several clipping stages in the circuit, but the final result will not really change.

As for the clipping technique, each manufacturer has his favorite approach: FET’s, OpAmps, regular diods, tubes, bipolar transistors, MOS-FET, etc…

Tom Scholz has selected the LED clipping technique, probably after a long series of tests and prototypes, and, why not, because LED’s light up when they clip!

“I don’t use tubes or transistors as overdrive elements; I use LED’s […] It doesn’t matter if it’s tubes, transistors or LED’s, if you do the right thing with them. On Third Stage, for instance, I started off using tube amps for several of the songs. I went back later and changed some of the parts so that some songs had pieces of tubes and Rockman. Nobody can tell which is which: I can only tell you because I was here (Guitar World, Feb. 90).”

The clipping element is a basis, the component that will create these artificial harmonics. As a standalone circuit, a clipping diod, transistor or tube sounds horrible. The art of distortion doesn’t stand in the choice of this clipping basis: it stands in what you connect before and after it to get something musical.

And what you place before and after are filters.

Copyright Rockman.fr 2007