Audio Effects Explained Series: Part 7 – Distortion
Sunday, January 18th, 2009This is the final installment of the Audio Effects Explained Series. Originally written for THRS episode 17.
Distortion Explained
I find it hard to think about the 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.
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.
Distortion Pedals
Overdrive Distortion
Overdrive distortion is a well-known distortion. While the general purpose is to emulate classic “warm-tube” sounds, distortion pedals can be distinguished from overdrive pedals in that the intent is to provide players with instant access to the sound of a high-gain Marshall amplifier such as the JCM800 pushed past the point of tonal breakup and into the range of tonal distortion known to electric guitarists as “saturated gain.” Some guitarists will use these pedals along with an already distorted amp or along with a milder overdrive effect to produce radically high-gain sounds. Although most distortion devices use solid-state circuitry, some “tube distortion” pedals are designed with preamplifier vacuum tubes. In some cases, tube distortion pedals use power tubes or a preamp tube used as a power tube driving a built-in “dummy load.”
The Boss DS-1 Distortion is a pedal with this design, this is what that sounds like.
[Listen to the Boss DS-1 Distortion Pedal]
Overdrive/Crunch
Some distortion effects provide an “overdrive” effect. Either by using a vacuum tube, or by using simulated tube modeling techniques, the top of the wave form is compressed, giving a smoother distorted signal than regular distortion effects. When an overdrive effect is used at a high setting, the sound’s waveform can become clipped, which imparts a gritty or “dirty” tone, which sounds like a tube amplifier “driven” to its limit. Used in conjunction with an amplifier, especially a tube amplifier, driven to the point of mild tonal breakup short of what would be generally considered distortion or overdrive,
or along with another, stronger overdrive or distortion pedal, these can produce extremely thick distortion. Today there is a huge variety of overdrive pedals including the Boss OD-3 Overdrive.
[Listen to the Boss OD-3 Overdrive Pedal]
Fuzz
Fuzz was originally intended to recreate the classic 1960’s tone of an overdriven tube amp combined with torn speaker cones. Oldschool guitar players would use a screwdriver to poke several holes through the the guitar amp speaker to achieve a similar sound. Since the original designs, more extreme fuzz pedals have been designed and produced, incorporating octave-up effects, oscillation, gating, and greater amounts of distortion. The Electro-Harmonix Big Muff is a classic fuzz pedal.
[Listen to the Electro-Harmonix Big Muff Fuzz Pedal]
Hi-Gain
Hi-Gain is the sound most used in Heavy metal. High gain in normal electric guitar playing simply references a thick sound produced by heavily overdriven amplifier tubes, a distortion pedal, or some combination of both–the essential component is the typically loud, thick, harmonically rich, and sustaining quality of the tone. However, the Hi-Gain sound of modern pedals is somewhat distinct from, although descended from, this sound. The distortion often produces sounds not possible any other way. Many extreme distortions are either hi-gain or the descendants of such.
An example of a hi-gain pedal is the Line 6 Uber Metal
[Listen to the Line-6 Uber Metal Distortion Pedal]
Power-tube pedal
Power tube distortion is a unique kind of saturation when tube amps output stages are overdriven, unfortunately this kind of really powerful distortion only happens at high volumes. A Power-Tube pedal contains a power tube and optional dummy load, or a preamp tube used as a power tube. This allows the device to produce power-tube distortion independently of volume.
An example of a tube based distortion pedal is the Ibanez Tube King
[Listen to the Ibanez Tube King Distortion Pedal]
Moving away from guitars there are a couple more ways to distort something.
Other Ways To Distort
Tape Saturation
One way 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.
Here’s a bass guitar with a bit of tape saturation from the Ferox vst plugin.
Digital Wave Shaping
The word clipping in recording is usually a bad thing. And generally it is, unless we’re trying to distort something on purpose. In the digital world we can use powerful wave shaping tools to drastically distort and manipulate a sound. Rather than subject you to the technical explanation of how it works, just listen to Nine Inch Nails, they use this a lot. It’s perfect for really harsh, aggressive, unnatural and broken sounds.
Here’s some examples of Ohmforce Ohmicide on a drum loop.
Why Is This Important?
Alright, so why did I just explain those different types of distortion sounds? Because knowing those sounds can help you be a better musician, engineer and producer. It will help you make decisions on what gear to purchase and what is appropriate for a song.
What Else?
Besides guitar what else is distortion good for? Well, pretty much anything, as long as it’s appropriate for the song.
- Slight distortion can make something sound more exciting, too much can sometimes make it really tiny sounding.
- When recording electric guitars, you can get a way bigger sound by using less gain and recording the same part multiple times, double or quad-tracking.
- Distortion can sound really cool on drums, but you may have to heavily gate the drums, the sustain can get out of control.
*Note: All the samples except the last two were copied from various internet sources, mostly manufacturer websites.
