3. Sound coding

Looking back at the development of MPEG digital audio standards since 1988, MPEG-4 Audio represents the 4th generation.

• In 1992, MPEG-1 Audio was standardized. It defines the coding-compression of one or two high-quality audio channels, sampled at 32, 44.1 or 48 kHz. It has a choice of 3 configurations, or layers, depending on the requirements of different applications. Layer 2 (total bitrate 32-384 kbit/s, transparency 128 kbit/s per channel) and layer 3 (MP3; total bitrate 32-320 kbit/s, transparency 96 kbit/s per channel) are the most widely used.

• In 1994, MPEG-1 Audio was complemented by MPEG-2 Audio, offering extensions with reduced sampling frequencies (16, 22.05 and 24 kHz) and a multichannel (5) stereo compatible mode (backward compatible,...