Glossary of Terms

sine wave

A waveform is a representation of how a sound varies in time. The most familiar waveform is the sine wave, which derives its name from the that that the sound varies with the "sine curve" of the elapsed time.

cosine wave

A cosine wave is a signal waveform with a shape identical to that of a sine wave, except each point on the cosine wave occurs exactly 1/4 cycle earlier than the corresponding point on the sine wave. A cosine wave and its corresponding sine wave have the same frequency, but the cosine wave leads the sine wave by 90 degrees of phase.

frequency

For an oscillating or varying sound, frequency is the number of complete cycles per second. The standard unit frequency is the hertz, abbreviated Hz. If a sound completes one cycle per second, then the frequency is 1 Hz; 60 cycles per second equals 60 Hz.

hertz

Hertz is a unit of frequency of a sound wave. The unite of measure is named after Heinrich Hertz, the German physicist.

harmonic spectrum

The combination of frequencies - and their amplitudes - that are present in a sound is called its spectrum (just as different frequencies and intensities of light constitute a color spectrum). Each individual frequency that goes into the makeup of a sound is called a partial or harmonic.

amplitude

Amplitude is the loudness of a sound often measured in decibels.

amplitude envelope

The shape of a sound over time measured in amplitude is the amplitude envelope. The initial portion is referred to as the attack of the sound, sometimes followed by sustain, and then by the decay.

sampling rate

The rate of discreet samples of a sound wave's instantaneous amplitude, in which the information is stored and then later reproduced at the same rate to create the illusion of a continuous sound wave. The sampling rate for CD quality is 44,100 Hz, DVD audio is typically sampled at 48,000 Hz.

decibel

The decibel (abbreviated as dB, and also as db and DB) is used as an absolute indicator of sound power per unit surface area on a scale from the threshold of human hearing, 0 dB, upwards towards the threshold of pain, about 120 - 140 dB. A decibel is one-tenth of a Bel, a seldom-used unit named for Alexander Graham Bell, inventor of the telephone.

analog-to-digital (ADC)

The conversion of an analog audio signal into a digital signal at a specific sampling rate. Microphone input is an example of adc conversion.

digital-to-analog (DAC)

The conversion of an digital audio signal into an analog signal, typically when the audio is sent from the computer or digital device to a mixer or amplifier for speaker diffusion.