3·588·25Hz = 44100 Hz

3·490·30Hz = 44100 kHz

1.001 1.001

≈ 44.056 kHz

Audio rates

Digital audio has two standard sample rates: 48 kHz, for professional applications, and 44.1 kHz, for consumer applications. In the standardization of digital audio, manufacturers decided to adopt two different standards in order that professional and consumer equipment could be differentiated! That goal failed miserably, and now the dichotomy in sample rates is a major nuisance in video and audio production.

The 44.1 kHz sampling rate for consumer digital audio originated from an early PCM recording system (Sony PCM-1600) that recorded three (16-bit) stereo sample pairs on 588 active lines of a 625/50 videocassette recorder. In 525/59.94 countries, the original rate was 44100⁄1.001: Three 16-bit stereo sample pairs were recorded on each of 490 active lines per frame. Eventually, the 44.1 kHz rate was standardized worldwide. In 1⁄50 s, there are 882 samples, an integer. In 1⁄59.94 s, there are exactly 1471.47 samples: the noninteger ratio causes havoc.

The professional audio sampling rate was chosen to be exactly 48 kHz. The time interval of one video picture at 50 fields or frames per second corresponds to exactly 960 audio samples at 48 kHz. An AES/EBU audio frame comprises 192 left/right sample pairs, with 16 bits in each sample: In 50 Hz video standards,

a video frame occupies exactly the same time interval as five audio frames. In video at 59.94 fields or frames per second, the timing relationships are unfortunate. There are 16013⁄5 audio sample intervals in one picture time: This noninteger number is very inconvenient. The timing relationship of audio samples to video pictures

aligns just once every five pictures. There are 1001⁄240

_

(i.e., 4.170833) AES/EBU audio frames in a video picture time.