The Full Wiki

Linear pulse code modulation: Wikis

Advertisements
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Encyclopedia

From Wikipedia, the free encyclopedia

Linear pulse code modulation
Filename extension .L16, .WAV, .AIFF,[1] .AU, .PCM, and many others
Internet media type audio/L16, audio/L8,[2], audio/L20, audio/L24[3][4]
Type code "AIFF" for L16,[1] none[3]
Magic number none
Type of format uncompressed audio
Contained by Audio CD, AES3, WAV, AIFF, AU, M2TS, VOB, and many others
Extended from PCM

Linear pulse code modulation (LPCM) is a method of encoding audio information digitally. The term also refers collectively to formats using this method of encoding. The term PCM, though strictly more general, is often used to describe data encoded as LPCM.

Contents

Description

LPCM is a particular method of pulse code modulation which represents an audio waveform as a sequence of amplitude values recorded at a sequence of times.

LPCM specifies that the values stored are proportional to the amplitudes, rather than representing say the logarithm of the amplitude, or being related in some other manner (companding). In practice these values will be quantized.

Implementations

LPCM is the method of encoding generally used in conjunction with the WAV container format, the de facto standard for uncompressed audio on PCs. The term PCM and LPCM often refer explicitly to the format used in WAV files, though LPCM data may also be commonly stored in other formats such as AIFF. LPCM is further used for the lossless encoding of audio data in the compact disc Red Book standard. LPCM has been defined as a part of the DVD and Blu-ray standards.[5][6] AES3 is a particular format using LPCM. Linear pulse code modulation is used by HDMI. It is used in RF64 container format that also allows non-PCM bitstream storage: various compression formats contained in the RF64 file as data bursts (Dolby E, Dolby AC3, DTS, MPEG-1/MPEG-2 Audio) can be "disguised" as PCM linear.[7]

Standard sampling resolutions and rates

Common sample resolutions for LPCM are 8, 16, 20 or 24 bits per sample.[1][2][3][8]

LPCM encodes a single sound channel. Support for multichannel audio depends on file format and relies on interweaving or synchronization of LPCM streams.[9][10] While two channels (stereo) is the most common format, some can support up to 8 audio channels (7.1 surround).[2][3]

Common sampling frequencies are 48 kHz as used with DVD format videos, or 44.1 kHz as used in compact discs. Sampling frequencies of 96 kHz or 192 kHz can be used on some newer equipment, with the higher value equating to 6.144 megabit per second for two channels at 16-bit per sample value. The bitrate limit for LPCM audio on DVD-Video is also 6.144 Mbit/s, allowing 8 channels (7.1 surround) x 48 kHz x 16-bit per sample = 6144 kbit/s.

DVD standards

Most DVD players only support 48 kHz/16-bit capability. Only more high-end players have built-in 96 kHz/24-bit capabilities. The DVD-Audio standard supports 192 kHz/24-bit playback.

See also

References

  1. ^ a b c "RFC 2586 - The Audio/L16 MIME content type". 1999-05. http://tools.ietf.org/html/rfc2586. Retrieved 2010-03-16. 
  2. ^ a b c "RFC 4856 - Media Type Registration of Payload Formats in the RTP Profile for Audio and Video Conferences - Registration of Media Type audio/L8". 2007-03. http://tools.ietf.org/html/rfc4856#page-17. Retrieved 2010-03-16. 
  3. ^ a b c d "RFC 3190 - RTP Payload Format for 12-bit DAT Audio and 20- and 24-bit Linear Sampled Audio". 2002-01. http://tools.ietf.org/html/rfc3190. Retrieved 2010-03-16. 
  4. ^ "Audio Media Types". Internet Assigned Numbers Authority. http://www.iana.org/assignments/media-types/audio/. Retrieved 2010-03-16. 
  5. ^ Blu-ray Disc Association (2005-03) (PDF), White paper Blu-ray Disc Format - 2.B Audio Visual Application Format Specifications for BD-ROM, http://www.blu-raydisc.com/Assets/Downloadablefile/2b_bdrom_audiovisualapplication_0305-12955-15269.pdf, retrieved 2009-07-26 
  6. ^ "DVD Technical Notes (DVD Video - "Book B") - Audio data specifications". 1996-07-21. http://www.mpeg.org/MPEG/DVD/Book_B/Audio.html. Retrieved 2010-03-16. 
  7. ^ EBU (2009-07) (PDF), EBU Tech 3306 - MBWF / RF64: An Extended File Format for Audio, http://tech.ebu.ch/docs/tech/tech3306-2009.pdf, retrieved 2010-01-19 
  8. ^ "RFC 3108 - Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections". 2001-05. http://tools.ietf.org/html/rfc3108#page-62. Retrieved 2010-03-16. 
  9. ^ Library of Congress, PCM, Pulse Code Modulated Audio, Retrieved on 2009-07-18
  10. ^ Library of Congress, Linear Pulse Code Modulated Audio (LPCM), Retrieved on 2009-07-18

External links

Advertisements

Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message