Pulse-code modulation

"PCM" redirects here. For other uses, see PCM (disambiguation).

Pulse-code modulation
Filename extension
.L16, .WAV, .AIFF, .AU, .PCM[1]
Internet media type
audio/L16, audio/L8,[2] audio/L20, audio/L24[3][4]
Type code"AIFF" for L16,[1] none[3]
Magic numberVaries
Type of formatUncompressed audio
Contained byAudio CD, AES3, WAV, AIFF, AU, M2TS, VOB, and many others
Open format?Yes
Free format?Yes[5]
Passband modulation
Analog modulation
Digital modulation
Hierarchical modulation
Spread spectrum
See also

Pulse-code modulation (PCM) is a method used to digitally represent analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. Alec Reeves, Claude Shannon, Barney Oliver and John R. Pierce are credited with its invention.[6][7][8]

Linear pulse-code modulation (LPCM) is a specific type of PCM in which the quantization levels are linearly uniform.[5] This is in contrast to PCM encodings in which quantization levels vary as a function of amplitude (as with the A-law algorithm or the μ-law algorithm). Though PCM is a more general term, it is often used to describe data encoded as LPCM.

A PCM stream has two basic properties that determine the stream's fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are taken; and the bit depth, which determines the number of possible digital values that can be used to represent each sample.

  1. ^ a b Alvestrand, Harald Tveit; Salsman, James (May 1999). "RFC 2586 – The Audio/L16 MIME content type". The Internet Society. doi:10.17487/RFC2586. Retrieved March 16, 2010. {{cite journal}}: Cite journal requires |journal= (help)
  2. ^ Casner, S. (March 2007). "RFC 4856 – Media Type Registration of Payload Formats in the RTP Profile for Audio and Video Conferences – Registration of Media Type audio/L8". The IETF Trust. doi:10.17487/RFC4856. Retrieved March 16, 2010. {{cite journal}}: Cite journal requires |journal= (help)
  3. ^ a b Bormann, C.; Casner, S.; Kobayashi, K.; Ogawa, A. (January 2002). "RFC 3190 – RTP Payload Format for 12-bit DAT Audio and 20- and 24-bit Linear Sampled Audio". The Internet Society. doi:10.17487/RFC3190. Retrieved March 16, 2010. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ "Audio Media Types". Internet Assigned Numbers Authority. Retrieved March 16, 2010.
  5. ^ a b "Linear Pulse Code Modulated Audio (LPCM)". Library of Congress. April 19, 2022. Retrieved September 5, 2022.
  6. ^ Noll, A. Michael (1997). Highway of Dreams: A Critical View Along the Information Superhighway. Telecommunications (Revised ed.). Mahwah, NJ: Erlbaum. p. 50. ISBN 978-0-8058-2557-2.
  7. ^ Leibson, Steven (September 7, 2021). "A Brief History of the Single-Chip DSP, Part I". EEJournal. Retrieved September 19, 2024.
  8. ^ Barrett, G. Douglas (2023). Experimenting the Human: Art, Music, and the Contemporary Posthuman. Chicago London: The University of Chicago Press. p. 102. ISBN 978-0-226-82340-9.