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.
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Description
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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. AES3 is a particular format using LPCM. Linear pulse code modulation is used by HDMI.
Standard sampling resolutions and rates
Common sample resolutions for LPCM are 8, 16, 20 or 24 bits per sample.
LPCM encodes a single sound channel. Support for multichannel audio depends on file format and relies on interweaving or synchronization of LPCM streams.[1][2] While two channels (stereo) is the most common format, some can support up to 8 audio channels (7.1 surround).
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
- ^ 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
- 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.
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