Zephyr/IP Audio Codecs
By far, the most popular high fidelity audio coders rely upon techniques developed under the MPEG umbrella. MPEG stands for Motion Pictures Expert Group, a Joint Committee of the International Standards Organization (ISO) and the International Electrotechnical Commission.
In addition to the latest MPEG audio codec, MPEG AAC - Enhanced Low Delay, the Zephyr/IP also supports High Efficiency AAC, MPEG Layer-2, G.711, G.722 and uncompressed PCM (if you have the bandwidth available).
High audio quality, low coding delay and very low data rates: AAC Enhanced Low Delay (AAC-ELD) is the perfect choice for any delay critical application that demands full audio bandwidth at data rates down to 24 kbit/s. AAC-ELD combines the strengths of its two main components, MPEG-4 AAC Low Delay, and Spectral Band Replication (SBR). Whereas MPEG-4 AAC-LD features low encoding/decoding latency, SBR provides high quality audio at very low bit rates. SBR is also used in MPEG-4 HE-AAC, one of today’s most efficient audio codecs. AAC-ELD became an MPEG standard in January 2008.
The Z/IP manual includes a chapter (chapter 12) on audio coding which describes these codecs and some of the theory behind them in more detail. For your convenience we include this chapter here 
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