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About this Article
Written by: Russell Myers
Written on: February 1st, 2002
Tags: entertainment, electrical engineering
Thumbnail by: Kieff/Wikimedia Commons
About the Author
In Spring 2002, Russell Myers was a junior at the University of Southern California pursuing both an electrical engineering degree with an emphasis in digital signal processing, and a minor in music, studio performance guitar. Originally from Texas, he enjoyed wrestling bulls and overdriving amplifiers in his quasi-free time in college.
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Volume III Issue I > Engineering Rock and Roll: A Casual Introduction to Signal Processing
Audio distortion has become an accepted method of musical creation. A discussion of the wave properties of sound, the origin of distortion (due to both wave physics and audio device technology), and an overview of many types of distortion, including hard and soft clipping, even and odd harmonic distortion, speaker overdrive, amplifier non linear operation and intermodulation, are offered.

Introduction

For decades scientists and engineers have debated the source of the unique artistic genre commonly referred to as rock music. Several reputable sources claim that Elvis, with his Blue Suede Shoes, greased hair, and snarling lip brought together the raw, blues-driven sound. Others vehemently argue that The Beatles are responsible for fusing melody with sexual innuendo; after all, John Lennon was the first to harness guitar/amplifier feedback as an effect on the track, "I Feel Fine." Surprisingly, the answer to this troubling enigma lies in the fact that rock & roll's source is not so much a who, but a what: rock and roll's source is the signal processing effect known as distortion.
For most all engineering applications, distortion is actually an unwanted effect; by definition, it is the "undesired change in the waveform of a signal." Our contemporary digital age of electronics is designed to limit distortion in order to improve signal accuracy. Although this may all be well and good, in the aural world musicians and engineers have embraced this phonetic accident, and with it developed an unlikely tool for artistic expression. Auditory distortion most likely was accidentally discovered in a live musical setting. In order for the sound to reach an audience spread across a large area, the speaker amplitude level must be relatively high. When these levels surpass the amplifier's linear range of operation, amplifier overdrive occurs, and the result is distortion. Given that rock music and loudness are inextricable entities, although first mildly associated with the genre, distortion has quickly become essential when one defines rock [1].
Although its birth was an unplanned event, audio distortion has matured into a science of its own. The two main components in distortion are the original signal and the amplifier through which this signal is processed. The processes by which distortion is produced vary as much as the sounds; since the 1950's engineers and musicians have worked together to produce endless tone and fuzz combinations.
To some it may just be noise, but auditory distortion is actually a highly complex phenomena (Fig. 1). Physics, mathematics, musicianship and electrical engineering must all coalesce in order to manufacture a desirable sound. The accidental circumstance of its discovery explains the reason for its complexity; engineers must reproduce this chance accident consistently and specifically.

The Nature of Sound: Waves 101

Kieff/Wikimedia Commons
Figure 1: Sinusoidal waves of different frequencies.
In order to understand the electro physics of distortion, one must first gain a basic understanding of the nature of sound. Sound is produced when an event causes a mechanical oscillation that disturbs the adjacent medium, namely air. The air molecules then begin to oscillate with the same frequency as the source and create a pressure wave having periods of compression and rarefaction. When this pressure strikes the human ear drum, the energy is then converted back into mechanical form, and is ultimately processed by the brain as sound. Although sound is independently transferred by a longitudinal wave, the actual information is packaged in a superposition of sinusoidal wave.
Sound's infinitely unique possibilities result from altering the characteristics of sound waves. In music, a note's pitch is directly related to the wave's frequency. Likewise, the auditory loudness of a sound is dictated by the wave's amplitude. Thus, in order for an opera singer to achieve glass-breaking sound, she must produce a wave high in both frequency and amplitude.