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The selection of the sample rate was based primarily on the need to reproduce the audible frequency range of 20–20,000 Hz (20 kHz). The Nyquist–Shannon sampling theorem states that a sampling rate of more than twice the maximum frequency of the signal to be recorded is needed, resulting in a required rate of greater than 40 kHz.
When is normalized with reference to the sampling rate as ′ =, the normalized Nyquist angular frequency is π radians/sample. The following table shows examples of normalized frequency for f = 1 {\displaystyle f=1} kHz , f s = 44100 {\displaystyle f_{s}=44100} samples/second (often denoted by 44.1 kHz ), and 4 normalization conventions:
High-resolution audio (high-definition audio or HD audio) is a term for audio files with greater than 44.1 kHz sample rate or higher than 16-bit audio bit depth. It commonly refers to 96 or 192 kHz sample rates. However, 44.1 kHz/24-bit, 48 kHz/24-bit and 88.2 kHz/24-bit recordings also exist that are labeled HD audio.
Some professional recording and production equipment is able to select 96 kHz sampling. This sampling frequency is twice the 48 kHz standard commonly used with audio on professional equipment. 176,400 Hz Sampling rate used by HDCD recorders and other professional applications for CD production. Four times the frequency of 44.1 kHz.
The standard is defined in the Red Book technical specifications, which is why the format is also dubbed "Redbook audio" in some contexts. [1] CDDA utilizes pulse-code modulation (PCM) and uses a 44,100 Hz sampling frequency and 16-bit resolution, and was originally specified to store up to 74 minutes of stereo audio per disc.
Audio on Compact Disc has a sampling rate of 44.1 kHz; to transfer it to a digital medium that uses 48 kHz, method 1 above can be used with L = 160, M = 147 (since 48000/44100 = 160/147). [5] For the reverse conversion, the values of L and M are swapped.
The DVD format uses the 48 kHz sampling rate, and its doublings. In digital audio, 48,000 Hz (also represented as 48 kHz or DVD Quality) is a common sampling rate. It has become the standard for professional audio and video. 48 kHz is evenly divisible by 24, a common frame rate for media, such as film, unlike 44.1 kHz. [i]
For example, for human hearing bandwidth between 0 and 20 kHz, audio must be sampled at above 40 kHz. Due to the need for filtering out ultrasonic frequencies resulting from the conversion to an analog signal, in practice slightly higher sample rates are used: 44.1 kHz or 48 kHz .