The sound of a guitar tone is instantly identifiable to most people. While there are subtle differences between different types of guitars, its physical construction and the way that it is played determines its basic tonal character. The guitar is a stringed musical instrument, with the acoustic vibration of its strings amplified by a hollow box called the body.
Attached to the body is a long, slender neck that is topped by a headstock. Strings are attached at one end to a slightly raised bridge on the body, and traverse over a hole cut into the body. A the other end, the strings are attached to a screw-and-gear mechanism in the headstock that adjusts the tension, or tuning, of the strings. These basic elements of a guitar can vary, from the size and shape of the body, to the length of the neck, or to the size of the sound hole.
Classical and flamenco guitars are usually fitted with "nylon" strings, or monofilaments of plastic. The most popular guitars, the flat-top dreadnaught, are usually fitted with "steel" strings, or alloys of steel, nickel, and bronze. The latter produces a guitar tone which is louder and brighter. The number of strings on a guitar varies by type, anywhere from four to 18; the most common is six.
There are several common guitar tunings, but the standard is the E note above Middle C, followed by B, G, D, A and E, in descending order. When a string is fingered against the guitar's neck, its length is shortened and its pitch is correspondingly raised. The standard tuning enables multiple strings to be variously fingered and played simultaneously as many different musical chords. When several, or all, of the strings are struck in musical time — a stroke called strumming — the resulting rhythmic choral sound is a uniquely guitar tone.
The strings can also be individually plucked, either with fingers or with a pointed pick, to play single notes. The essence, or sonic waveform, of the guitar tone can be explained by this playing method. The tone has a sharp attack, because a string is either struck or not, and that instant is when the string sounds loudest. It has a strong, oscillating vibrato, with the length and tension of a guitar's string causing a large vibration. It has a long decay, because the hollow body acts as an echo chamber.
The instrument's timbre, or resonance, is more difficult to define, but nevertheless unique. There are two characteristics contribute to it. First, guitar strings vibrate at not just one frequency but multiple secondary harmonic overtones. Second, the shape of the hollow body bounces and deforms sound waves in a particular pattern. An electric guitar is fundamentally the same as an acoustic guitar except that its nearly inaudible tone is picked up, processed, and amplified electronically.