Page 8

The results were remarkable for AAC. At 96 kbps, it give comparable quality to Layer 2 at 192 kbps and to Layer 3 at 128 kbps. The researchers concluded that there was a clear performance distinction among the various codecs: 

The results show that the codec families are clearly delineated with respect to quality. The ranking of the codec families with respect to quality is: AAC, PAC, Layer 3, AC-3, Layer 2, and ITIS (a Layer 2 implementation). The highest audio quality was obtained for the AAC codec operating at 128 kbps and the AC-3 codec operating at 192 kbps per stereo pair.

The following trend is found for codecs rated at the higher end of the subjective rating scale. In comparison to AAC, an increase in bitrate of 32, 64, and 96 kbps per stereo pair is required for the PAC, AC-3, and Layer 2 codec families respectively to provide the same audio quality.

Finally, the CRC study concluded that AAC achieves the ITU ?indistinguishable quality? goal ? the first codec to fulfill this requirement at 128 kbps/stereo:

The AAC codec operating at 128 kbps per stereo pair was the only codec tested which met the audio quality requirement outlined in the ITU-R Recommendation BS.1115 for perceptual audio codecs for broadcast.

AAC at 128 kbps/stereo measured higher than any of the codecs tested. It has approximately 100% more coding power than Layer 2 and 30% more power than the former MPEG performance leader, Layer 3.