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Term: Sampling rate (audio)

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Term: Sampling rate (audio)


Sampling rate or sampling frequency defines the number of samples per second (or per other unit) taken from a continuous signal to make a discrete or digital signal. For time-domain signals like the waveforms for sound (and other audio-visual content types), frequencies are measured in in hertz (Hz) or cycles per second. The Nyquist–Shannon sampling theorem (Nyquist principle) states that perfect reconstruction of a signal is possible when the sampling frequency is greater than twice the maximum frequency of the signal being sampled. For example, if an audio signal has an upper limit of 20,000 Hz (the approximate upper limit of human hearing), a sampling frequency greater than 40,000 Hz (40 kHz) will avoid aliasing and allow theoretically perfect reconstruction.

Many authorities in the preservation of sound recordings, like the International Association of Sound and Audiovisual Archives (IASA), recommend sampling rates that encode audio outside range of human hearing range, i.e., rates well above 40 kHz. IASA document TC-04 states that higher sampling rates "may be advantageous for many content types. . . . The net effect of higher sampling rate and conversion technology improves the audio quality within the ideal range of human hearing. The unintended and undesirable artefacts inherent in a recording are also part of the sound document, whether they were inherent in the manufacture of the recording or have been subsequently added to the original signal by mishandling or poor storage. Both must be preserved with utmost accuracy. For some types of noise, sampling rates in excess of 48 kHz may be advantageous. For any higher sampling rates IASA recommends 96 kHz."

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