DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

3· 588· 25 Hz = 44100 Hz
3 490 30 Hz 44100
· · = kHz
1. 001 1. 001
≈ 44. 056 kHz
The 44.1 kHz sampling rate for consumer digital audio
originated from an early PCM recording system that
recorded three, 16-bit stereo sample pairs on 588
active lines of a 625/50 U-matic VCR. 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.
The professional audio sampling rate was chosen to be
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 1601 3 ⁄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.
At the consumer audio rate, there are 882 samples in
1 ⁄50 s; an integer. There are exactly 1471.47 samples in
1 ⁄59.94 s; again, the noninteger ratio causes havoc.
380 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES