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Tue 26 Dec 06 @ 12:33 am
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Acoustics / Electroacoustics
The pattern of SOUND PRESSURE variation, usually displayed as a two-dimensional graph of pressure or AMPLITUDE against time (see OSCILLOSCOPE). For PERIODIC waveforms, a single CYCLE or PERIOD defines the waveform. Also called sound pressure function, particularly when represented digitally.
The simplest waveform is the SINE WAVE, since it has only one FREQUENCY associated with it. More complex waveforms can be constructed from sine waves of various frequencies by the LAW OF SUPERPOSITION. Common waveforms used in SOUND SYNTHESIS are the TRIANGLE WAVE, SQUARE WAVE, SAWTOOTH WAVE and PULSE WAVE. These AUDIO waveforms are often termed fixed waveforms because of their lack of variation, whereas acoustic waveforms are constantly varying.
The waveform represents the behaviour of the sound in the time domain, and since its shape is indicative of the frequency content of the sound, waveform is sometimes used synonymously with TIMBRE, although all contributing factors to timbre cannot be understood simply in terms of the waveform.
SINE WAVE
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Acoustics / Electroacoustics
A sinusoidal wave or function, that is, one moving in SIMPLE HARMONIC MOTION according to the function
A sin (2pft)
where A is the AMPLITUDE of the wave, f its FREQUENCY, and t is time.
According to the FOURIER THEOREM, any periodic WAVEFORM may be analyzed as the sum of a series of sine waves with frequencies in a HARMONIC SERIES, each of which has an amplitude and phase angle given by the Fourier coefficients. Since a sine wave has only a single frequency associated with it, it may be considered the simplest sound.
Frequency is denoted by the symbol f, and is measured in hertz (Hz) - formerly called cycles per second (cps or c/s) - kilohertz (kHz), or megahertz (mHz).
triangular wave. An audio WAVEFORM theoretically comprised of an infinite set of odd harmonic SINE WAVEs.
square wave
sawtooth
A sound with a short ENVELOPE, usually with a less sharp ATTACK than a CLICK. Also called an impulse
In electronics, the pulse is a rectangular DIRECT CURRENT voltage SIGNAL produced by a pulse GENERATOR. Its form could be described as an on-off voltage, where the 'on' voltage has a duration of t1 and is repeated after an interval of t2, during which the voltage drops to the 'off' level. Pulses can be used to control a SWITCH.
