MPEG-2 Part 3

Part 3 of the MPEG-2 standard defines audio coding:

MPEG Multichannel - It enhances MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel. This method is backwards-compatible, allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation.
MPEG-2 Part 3 also defined additional bit rates and sample rates for MPEG-1 Audio Layer I, MPEG-1 Audio Layer II and MPEG-1 Audio Layer III.

The MPEG-2 Part 3 should not be confused with MPEG-2 Part 7: AAC a.k.a. MPEG-2 NBC - the MPEG-2 Advanced Audio Coding with support for multichannel encoding.

Overview

MPEG-2 Part 3 introduced new audio encoding methods compared to MPEG-1 Part 3: MPEG-2 BC

low bitrate encoding with halved sampling rate
multichannel encoding with up to 5.1 channels