Shewbox.org

sub specie aeternitatis

Origin of the CD Sampling Rate

September 21, 2004

Reading “Essentials of Music Technology” by Mark Ballora, I came across a section that explains one reason why CD Audio has the sampling rate it does, 44.1kHz. I’ll just post the passage here:

When digital audio recording began, audio tape was not capable of storing the density of digital signals. The first digital masters were stored on videotape as a pseudo video signal in which sample values represented as binary numbers with digits of one and zero were stored as video levels of black-and-white. The sampling rate was determined by the format of videotape. Video pixels are drawn left to right in horizontal lines starting from the top of the screen and moving down. First the odd-numbered lines are drawn, then the even-numbered lines. Thus, each frame of video has two subsets: the odd field and even field. The fields lie adjacent to each other on the videotape in a diagonal orientation. There are two video broadcast formats:

1. USA (NTSC): 525 lines, 30 frames per second, minus 35 blank lines, leaving 490 lines per frame, equals 60 fields per second, 245 lines per field.

2. European (PAL): 625 lines, 25 frames per second, minus 37 blank lines, leaving 588 lines per frame, equals 50 fields per second, 294 lines per field.

With the pseudo format of black and white pixels, three samples could be stored on each line, allowing:

NTSC: 60 x 245 x 3 = 44,100 samples per second
PAL: 50 x 294 x 3 = 44,100 samples per second

Although videotapes are no longer necessary for storing digital audio, 44.1kHz remains the standard sampling rate for CD audio.

Interesting isn’t it? The premier audio medium still in use today is technology that is over 20 years old, and its quality is based on the sampling rate that could fit on a videotape.