PCM (Pulse Code Modulation) or LPCM (Linear pulse-code modulation) is an uncompressed lossless audio codec to digitally represent sampled analog signals. It is the same codec used in Redbook Audio CDs and Laserdiscs, except it has a high bit rate of 27.648 Mbit/s (3.456 MB memory) and up to 24-bit resolution. It is the best out of the audio codecs. 

Movie and Music soundtracks that use PCM audio usually store it in the WAVE file format. It is under the .wav extension name, which is located inside the m2ts container. Waveform Audio File Format (WAVE) was created in 1991 by Microsoft and IBM as a standard for storing uncompressed bitstream audio. It is natively coded in little-endian byte order. WAV is based on the Resource Interchange File Format (RIFF) bitstream format method for storing data in chunks. A RIFF file is a tagged file format and all WAV files use a RIFF tree structure:

File Root
│
└─ RIFF:WAVE  - RIFF Wave header
    ├─  fmt   - Wave format chunk
    └─ data  - Waveform data chunk

WAV's magic number is  52 49 46 46 xx xx xx xx 57 41 56 45 66 6D 74 20 " RIFF....WAVEfmt".

Another advantage is that it's an open format, meaning anyone can use the codec without restrictions or paying royalties. However, one disadvantage is that it takes up a lot of space because it's uncompressed. Early BD releases used PCM for movie titles as it's primarily audiotrack, but now major studios often use DTS and Dolby to conserve space and better compression. But, PCM is still used for Pure Audio BD music albums for the niche audiophile market and movies/TV shows from boutique labels.

 

Interactive Audio

BD uses PCM-based interactive audio for real-time interactive sound effects, usually for menus or video games.

 

    See: Interactive Audio

 

Auro-3D Extension

Auro-3D is an immersive audio codec that serves as an extension of PCM by adding additional height channels and additional metadata. It is backwards compatible with standard PCM and audio equipment.

 

    See: Auro-3D

 

Footnotes

• [1] https://www.loc.gov/preservation/digital/formats/fdd/fdd000011.shtml

Links

• PCM description on MultimediaWiki
• Archive Team's page of PCM
• WAV (Applications) – List of applications known to use WAV

WAV Specifications

• Format spec
• File format info
• Another file format info text file
• MSDN: Registered FOURCC Codes and WAVE Formats
• WAVE and AVI Codec Registries (Historic Registry)

WAV Metaformat files

• Synalysis grammar file (for Hexinator / Synalize It!; more details)

WAV Sample files

• dexvert samples — audio/wav

External links

• Wikipedia: WAV
• WAV101 an audio file walkthrough
• Format preservation assessment

Author(s) : Æ Firestone