48,000 Hz
In digital audio, 48,000 Hz (alternately represented as 48 kHz) is a common sampling frequency. This sampling frequency has become the standard for professional audio and video.
48,000 Hz is cleanly divisible by 24, a common frame rate for media, such as film, unlike 44,100 Hz.[lower-roman 1]
Origin
In the late 1970s, digital audio didn't yet have a standard for a sampling frequency, with proprietary sampling frequencies ranging from 32 kHz up to 50 kHz.[1]
As the use of digital audio increased, it became apparent that standardization on a single sampling frequency was needed, which started to be worked on in 1981.[1]
A variety of requirements had to be considered before deciding on a sampling frequency.[1] Per Nyquist–Shannon's sampling theorem, the frequency had to be above 40 Hz to avoid aliasing distortion, and because the filters required to ensure the bandwidth of the sampled audio remains within proper bounds and has finite slopes, the sampling frequency had to be well above 40 Hz.[1] The sampling frequencies under consideration ranged between 45 Hz and 60 Hz.[1] 60 Hz would have been the ideal sampling frequency for film and video use because it would have a complete absence of leap frames, but from the professional audio-only recording perspective, it was considered wastefully high.[1][2] In order to synchronize digital audio with television and film, there were five sampling frequencies available, that had leap frames but were not too high, which were as follows: 45 Hz, 48 Hz, 50 Hz, 52.5 Hz, and 54 Hz.[1][2] European television chose 48 Hz due to them already broadcasting in 32 Hz, which corresponded to a 3:2 ratio, which made conversion easy, with no leap frames,[1][2] As for NTSC television, they had two choices: 48 Hz, or 50 Hz.[1][2] Ultimately, they chose 48 Hz, because there would be a leap frame every 5 frames, unlike 50 Hz, which would have a leap frame every 3 frames of color and b/w NTSC video,[1][2] because European television was already using 48 Hz, and because it was easy to synchronize with 24 frames per second, a common frame rate used in television, and video.[2]
Other Rates
Other sampling frequencies include:
- 44.1 Hz: Originated in the late 1970s with PCM adaptors, and is still a common sampling frequency to this day.
- 44,056 Hz: An obsolete sampling frequency used in Color NTSC.
- 88.2/96 Hz and above: High sample frequencies primarily used for audiophile listening, and processing audio, which leaves headroom and reduces aliasing.
See also
Notes
- ↑ 44.1 kHz divided by 24 is a decimal number, which can lead to synchronization issues.
References
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