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Linear pulse-code modulation

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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 numbervaries
Type of formatuncompressed audio
Contained byAudio CD, AES3, WAV, AIFF, AU, M2TS, VOB, and many others
Extended fromPCM

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.[5] 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).

LPCM audio is coded using a combination of various parameters such as audio bit depth, sampling rate, signedness, number of channels (monaural, stereo, quadrophonic, etc.), interleaving of channels and endianness.

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.[6][7][8] It is also defined as a part of various digital video and audio storage formats (e.g. DV since 1995,[9] AVCHD since 2006[10]).
  • 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.[11]

Standard sampling resolutions and rates

Common sample resolutions for LPCM are 8, 16, 20 or 24 bits per sample.[1][2][3][12]

LPCM encodes a single sound channel. Support for multichannel audio depends on file format and relies on interweaving or synchronization of LPCM streams.[5][13] 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, but the benefits have been debated[14]. 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

  1. ^ a b c Alvestrand, Harald Tveit; Salsman, James (May 1999). "RFC 2586 – The Audio/L16 MIME content type". The Internet Society. Retrieved 2010-03-16.
  2. ^ a b c 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. Retrieved 2010-03-16.
  3. ^ a b c d 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. Retrieved 2010-03-16.
  4. ^ "Audio Media Types". Internet Assigned Numbers Authority. Retrieved 2010-03-16.
  5. ^ a b c "Linear Pulse Code Modulated Audio (LPCM)". Library of Congress. Retrieved 2010-03-21.
  6. ^ Blu-ray Disc Association (2005-03), White paper Blu-ray Disc Format – 2.B Audio Visual Application Format Specifications for BD-ROM (PDF), retrieved 2009-07-26 {{citation}}: Check date values in: |date= (help)
  7. ^ "DVD Technical Notes (DVD Video – "Book B") – Audio data specifications". 1996-07-21. Retrieved 2010-03-16.
  8. ^ Jim Taylor. "DVD Frequently Asked Questions (and Answers) – Audio details of DVD-Video". Retrieved 2010-03-20.
  9. ^ "How DV works". Archived from the original on 2007-12-06. Retrieved 2010-03-21.
  10. ^ "AVCHD Information Website – AVCHD format specification overview". Retrieved 2010-03-21.
  11. ^ EBU (2009-07), EBU Tech 3306 – MBWF / RF64: An Extended File Format for Audio (PDF), retrieved 2010-01-19 {{citation}}: Check date values in: |date= (help)
  12. ^ "RFC 3108 – Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections". 2001-05. Retrieved 2010-03-16. {{cite web}}: Check date values in: |date= (help)
  13. ^ "PCM, Pulse Code Modulated Audio". Library of Congress. Retrieved 2009-07-18.
  14. ^ "24/192 Music Downloads, and why they do not make sense". Chris "Monty" Montgomery. Retrieved 2013-03-16.
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