TheBigBlack's Guide To Digital Audio

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What Is Sample Rate & Sample Format (Bit Depth)?

Sample Rate represents the number of digital samples captured per second in order to represent the waveform. The more samples per second, the higher the sound resolution, and thus the more precise the measurement is of the waveform. Sample rates are measured in hertz (Hz), or cycles per second.

In the image below, the left half has a low sample rate (i.e. low resolution / quality), and the right half has a high sample rate (i.e. high resolution / quality):

Waveform

The human ear is sensitive to sound patterns with frequencies between approximately 20Hz and 20,000Hz (20Hz being the lowest frequencies, and 20,000Hz being the highest). Sounds outside that range are essentially inaudible by humans, although Rupert Neve has subjectively proven the existence of psychoacoustic fidelity that can be heard above this supposed limit of 20,000Hz. (Interestingly, only infants can hear audio in the 20,000hz frequency range. Most adults cannot hear much above 16,000Hz.)

Capturing a sound at a particular frequency requires a sampling rate of at least twice that frequency. This is known as the Nyquist Frequency. Therefore a sample rate of 40,000Hz is the absolute minimum necessary to reproduce sounds within the range of human hearing, though higher rates (called oversampling) may increase quality even further by avoiding any aliasing artifacts around the Nyquist Frequency.

Human speech is intelligible even if frequencies above 4,000Hz are eliminated - in fact land-line telephones only transmit frequencies between 200Hz and 4,000Hz. Therefore a common sample rate for spoken audio recordings is 8,000Hz (which is sometimes called Speech Quality).

 

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Last Updated: 25/09/2016