Several audio formats exist under the MPEG umbrella. These are all based on perceptual encoding techniques (covered later in this chapter).
A group of audio formats referred to as Layers I, II, and III are part of both MPEG-1 and MPEG-2. (AAC is part of MPEG-2, but it is not considered an MPEG layer.) Each layer uses the same basic structure and includes the features of the layers below it. Higher layers offer progressively better sound quality at comparable bit-rates and require increasingly complex encoding software. This, in turn, requires more processing power for encoding and decoding the audio.
MPEG Audio Layer-I was originally designed for the Digital Compact Cassette (DCC) and is not widely used.
MPEG Audio Layer-II (also referred to as MP2) is widely used within the broadcasting industry. Layer-II was designed as a tradeoff between complexity and performance and offers very high-quality sound at higher bit-rates (256 kbps and up). MP2 also has lower encoding delays than MP3, which is important for live broadcasting.
MPEG Audio Layer-III (MP3) was designed for better quality at lower bit-rates, which is very important because of the limited bandwidth of the Internet. MP3 is supported on all popular operating systems and by most jukebox programs and portable digital audio players.
AAC (Advanced Audio Coding) is not an MPEG layer, although it does use a perceptual encoding model. Sometimes referred to as MP4, AAC provides ...