LPCM
From Wikipedia, the free encyclopedia
Linear Pulse Code Modulation used in communications (or 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 for LPCM.
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[edit] 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. In practise these values will be quantized.
[edit] Implementations
LPCM is the method of encoding generally used with the WAV file format, the de facto standard for uncompressed audio on computers, though the WAV format can actually use several methods of encoding. The term PCM and LPCM often refer explicitly to the format used in WAV files. LPCM may also be used by the AIFF file format.
LPCM is further used for the encoding compact discs. LPCM has been defined as a part of the DVD standard. AES3 is a particular format using LPCM.
[edit] Standard sampling rates
Common sampling frequencies for formats of LPCM are 8, 16, 20, 24 or 32 bits per sample. Some formats support upto 8 audio channels.
Common sampling frequencies are 48 kHz, or 44.1 kHz as used in compact discs. Though sampling frequencies of 96 kHz or 192 kHz can be used on some newer equipment, with the higher value equating to 6.144 megabits per second per audio channel.
[edit] DVD Standards
Most DVD players only support 48 kHz/16-bit capability. Only more expensive players have built-in 96 kHz/24-bit capabilities.
To start enjoying the benefits of 24-bit/96 kHz LPCM audio, you will need to make sure you have the right hardware to support it. For the PC, you will need to have a sound card that fully supports 24-bit/96 kHz LPCM. In addition to that, the DVD movie you are playing has to be recorded in 24-bit/96 kHz LPCM format (generally these are musicals or concerts).
[edit] See also
[edit] 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.
