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Linear pulse-code modulation

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Title: Linear pulse-code modulation  
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Subject: Compact Disc Digital Audio, Ripping, HDMI, Ashes of the Wake, Comparison of container formats, 7.1 surround sound, Audio bit depth, Bose 2.1 home entertainment systems, Bose 5.1 home entertainment systems, Blu-ray Disc
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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 varies
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.[5] LPCM specifies that the values stored are proportional to the amplitudes, rather than representing say the logarithm of the amplitude (e.g., compandingA-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

External links

  • Summary of LPCM – Contains links to information about implementations and their specifications.
  • How to control internal/external hardware using Microsoft's Media Control Interface – Contains information about, and specifications for the implementation of LPCM used in WAV files.
  • RFC 4856 – Media Type Registration of Payload Formats in the RTP Profile for Audio and Video Conferences – audio/L8 and audio/L16 (March 2007)
  • RFC 3190 – RTP Payload Format for 12-bit DAT Audio and 20- and 24-bit Linear Sampled Audio (January 2002)
  • RFC 3551 – RTP Profile for Audio and Video Conferences with Minimal Control – L8 and L16 (July 2003)
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