Multichannel Pulse-Code Modulation (MPCM) is a modulation that is used for digital disc formats.
Overview
With MPCM, The audio on a DVD is compressed, normally using Dolby Digital or DTS encoding. As they are compressed formats they are naturally lossy by nature.
With Bluray discs, there is room for non-compressed audio, which is called MPCM or 5.1 Uncompressed. MPCM can only be utilized through an HDMI cable, and through certain home audio receivers. It is not normally turned on by default, meaning that the user must choose MPCM or 5.1 Uncompressed to utilize uncompressed audio.
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