MPEG defined three levels or layers of audio compression. Which layer a type of equipment uses depends on the desired level of compression. These three layers compress audio data streams by roughly four, six and eight times respectively, around 64, 128 and 192Kbit/s per channel. In practical terms, these compression rates make possible radio broadcasting of CD-quality music. All three layers are defined for both monaural and stereo sound. Definitions for surround sound and other high fidelity applications are under consideration.
