Distortion Explained Part 1

Distortion Explained Part 1

It is hard to think about the sound of an electric guitar without thinking about distortion. There was a time when electric guitars were always clean. Hard to imagine now.

Traditionally distortion was an unwanted feature in amplifier design. Distortion only occurred when the amp was damaged or overdriven. Possibly the first intentional use of distortion was in the 1951 recording of “Rocket 88″ By Ike Turner and the Kings of rhythm.

Chuck Berry liked to use small tube amps that were easy to overdrive for his trademark sound and other guitarists would intentionally damage their speakers by poking holes in them, causing them to distort.

Leo Fender then started designing amps with some light compression and slight overdrive and Jim Marshall started to design the first amps with significant overdrive. That sound caught on quickly and by the time Jimi Hendrix was using Roger Mayer’s effects pedals, distortion would forever be associated with the electric guitar.

Not just for guitars
When you're recording and mixing, you can use a bit of distortion to give any sound more edge, grit, energy and excitement. Drums, vocals, bass, samples - they can all benefit from a touch of distortion at times. Understanding the different ways distortion can be created and how they sound can help you get better sounds and make better recordings.

So What Is Distortion?

The word distortion means any change in the amplified waveform from the input signal. In the context of musical distortion this means clipping the peaks off the waveform. Because both valves and transistors behave linearly within a certain voltage region, distortion circuits are finely tuned so that the average signal peak just barely pushes the circuit into the clipping region, resulting in the softest clip and the least harsh distortion. Because of this, as the guitar strings are plucked harder, the amount of distortion and the resulting volume both increase, and lighter plucking cleans-up the sound. Distortion adds harmonics and makes a sound more exciting.

Amp Distortion

Valve Overdrive

Before transistors, the traditional way to create distortion was with vacuum valves also known as vacuum tubes. A vacuum tube has a maximum input voltage determined by its bias and a minimum input voltage determined by its supply voltage. When any part of the input waveform approaches these limits, the valve’s amplification becomes less linear, meaning that smaller voltages get amplified more than the large ones. This causes the peaks of the output waveform to be compressed, resulting in a waveform that looks “squashed”. This is known as “soft clipping”, and generates even-order harmonics that add to the warmth and richness of the guitar’s tone. If the valve is driven harder, the compression becomes more extreme and the peaks of the waveforms are clipped. This adds additional odd-order harmonics, creating a “dirty” or “gritty” tone.

Valve distortion is commonly referred to as overdrive, as it is achieved by driving the valves in an amplifier at a higher level than can be handled cleanly. Multiple stages of valve gain/clipping can be “cascaded” to produce a thicker and more complex distortion sound. In some modern valve effects, the “dirty” or “gritty” tone is actually achieved not by high voltage, but by running the circuit at voltages that are too low for the circuit components, resulting in greater non-linearity and distortion. These designs are referred to as “starved plate” configurations.

Transistor Clipping
Transistor clipping stages, on the other hand, behave far more linearly within their operating regions, and faithfully amplify the instrument’s signal until the input voltage falls outside its operating region, at which point the signal is clipped without compression, this “hard clipping” or limiting. This type of distortion tends to produce more odd-order harmonics. Electronically, this is usually achieved by either amplifying the signal to a point where it must be clipped to the supply rails, or by clipping the signal across diodes. Many solid state distortion devices attempt to emulate the sound of overdriven vacuum valves.

So that is basically how Tube and Solid state amps create distortion. Let’s talk about some different types of distortion sounds as found in effects pedals.

Tape Saturation

Another way to create distortion is with magnetic tape. Magnetic tape has a natural compression and saturation when you send it a really hot signal. Even today, many artists of all genres prefer analog tape’s “musical”, “natural” and especially “warm” sound. Due to harmonic distortion, bass can thicken up, creating the illusion of a fuller-sounding mix. In addition, high end can be slightly compressed, which is more natural to the human ear. It is common for artists to record to digital and re-record the tracks to analog reels for this effect of “natural” sound. While recording to analog tape is likely out of the home studio budget, there are tape saturation plugins that you can use while mixing that simulate the effect quite well. Most tape saturation effects are modeling both the magnetic tape and overloading of electronics.

Part 2 will cover the differences between various types of guitar distortions - Overdrives, Fuzz, hi-gain and more.