AAC = Advanced Audio Coding

Thought as a successor to MP3, AAC is part of the MPEG-4 standard and can encode multichannel streams.

Used in iTunes.

HD621, G98DH, G68ADV, Bc Acoustiqe ACT A3, 5200C DSP33, NuForce Reference 9 monoblocks, 2x SB3's, Velodyne DD-15 & DD-12 Subwoofers and a Meridian sub.