Linear pulse-code modulation
Linear pulse-code modulation
| Filename extension |
.L16, .WAV, .AIFF,[1] .AU, .PCM |
| 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 pulse-code modulation (PCM), though strictly more general, is often used to describe data encoded as LPCM.
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 is PCM with linear quantization.[5]
LPCM represents sample amplitudes on a linear scale.[6] LPCM specifies that the values stored are proportional to the amplitudes, rather than representing say the logarithm of the amplitude (e.g., companding – A-law/u-law), or being related in some other manner (e.g., DPCM or ADPCM).[6] In practice these values will be quantized.
LPCM audio is coded using a combination of various parameters – such as resolution/sample size (e.g., 8, 16, 20, 24 bit, etc), frequency/sample rate (e.g., 8,000, 11,025, 16,000, 22,050, 24,000, 32,000, 44,100, and 48,000 Hz / "samples per second", etc), sign (signed or unsigned), number of channels (monaural, stereo, quadrophonic, etc) and interleaving of channels, byte order (little endian, big endian).[7] If the sample is 16-bit signed, the sample range is from −32768 to 32767, with a centerpoint of 0[8] (for example, signed LPCM data is used on Audio CD, DVD Video, 16-bit LPCM in WAV, audio/L16, etc.) If the sample is 16-bit unsigned, the sample range is from 0 to 65,535, with a centerpoint of 32,768.[7]
Implementations
LPCM is the method of encoding generally used for uncompressed audio, although there are other methods such as pulse-density modulation (used also on Super Audio CD).
- LPCM is used for the lossless encoding of audio data in the Compact disc Red Book standard (informally also known as Audio CD), introduced in 1982.
- AES3 (specified in 1985) is a particular format using LPCM.
- On PCs, the term PCM and LPCM often refer to the format used in WAV (defined in 1991) and AIFF audio container formats (defined in 1988). LPCM data may also be stored in other formats such as AU, raw audio format (header-less file) and various multimedia container formats.
- LPCM has been defined as a part of the DVD (since 1995) and Blu-ray (since 2006) standards.[9][10][11] It is also defined as a part of various digital video and audio storage formats (e.g. DV since 1995,[12] AVCHD since 2006[13]).
- Linear pulse-code modulation is used by HDMI (defined in 2002), a single-cable digital audio/video connector interface for transmitting uncompressed digital data.
- RF64 container format (defined in 2007) uses LPCM and 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.[14]
Standard sampling resolutions and rates
Common sample resolutions for LPCM are 8, 16, 20 or 24 bits per sample.[1][2][3][15]
LPCM encodes a single sound channel. Support for multichannel audio depends on file format and relies on interweaving or synchronization of LPCM streams.[16][17] 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) × 48 kHz × 16-bit per sample = 6,144 kbit/s.
DVD standards
Older DVD players only support 48 kHz/16-bit capability. Recent players have built-in 96 kHz/24-bit capabilities. The DVD-Audio standard supports 192 kHz/24-bit playback.
See also
References
- ^ a b c "RFC 2586 – The Audio/L16 MIME content type". 1999-05. http://tools.ietf.org/html/rfc2586. Retrieved 2010-03-16.
- ^ 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.
- ^ 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.
- ^ "Audio Media Types". Internet Assigned Numbers Authority. http://www.iana.org/assignments/media-types/audio/. Retrieved 2010-03-16.
- ^ "Linear Pulse Code Modulated Audio (LPCM)". The Library of Congress. http://www.digitalpreservation.gov/formats/fdd/fdd000011.shtml. Retrieved 2010-03-21.
- ^ a b "PCM Types". MultimediaWiki. http://wiki.multimedia.cx/index.php?title=PCM#PCM_Types. Retrieved 2010-03-20.
- ^ a b "PCM Parameters". MultimediaWiki. http://wiki.multimedia.cx/index.php?title=PCM#PCM_Parameters. Retrieved 2010-03-20.
- ^ "RFC 3551 – RTP Profile for Audio and Video Conferences with Minimal Control". 2003-07. p. 27. http://tools.ietf.org/html/rfc3551#page-27. Retrieved 2010-03-20.
- ^ 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
- ^ "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.
- ^ Jim Taylor. "DVD Frequently Asked Questions (and Answers) – Audio details of DVD-Video". http://dvddemystified.com/dvdfaq.html#3.6.2. Retrieved 2010-03-20.
- ^ "How DV works". http://seaspray.trinity-bris.ac.uk/~altwfaq/graphics/video/1394/1394formats.html. Retrieved 2010-03-21.
- ^ "AVCHD Information Website – AVCHD format specification overview". http://www.avchd-info.org/format/index.html. Retrieved 2010-03-21.
- ^ 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
- ^ "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.
- ^ Library of Congress, PCM, Pulse Code Modulated Audio, Retrieved on 2009-07-18
- ^ Library of Congress, Linear Pulse Code Modulated Audio (LPCM), Retrieved on 2009-07-18
External links