Pulse-Code Modulation (PCM) and the Dolby Digital® technology refer to different types of digital audio recordings. PCM is the conventional method for converting analog audio into digital audio. The PCM audio recorded on DVD is a two-channel digital, stereo audio track.
The Dolby Digital® technology, which was originally called AC3, was developed specifically for multi-channel applications, including film sound and digital surround sound in the home. Dolby Digital® technology uses a 5.1 or six channel format. The 5 channels include the Stereo left and right front channels, Stereo left and right surround channels, and the center channel. There is also, a Low Frequency Effects (LFE) channel for the subwoofer, which is counted as the 0.1 channel since it functions only when a deep base effect is needed.