The latest perceptual coders, such as MPEG AAC (Advanced Audio Coding, also known as "MP4"), can achieve at 128 kbps (stereo) quality rated as "indistinguishable" using the ITU standard testing procedures. Moreover, "near CD" quality can be achieved at compression ratios as high as 16:1!
SPECTRAL BAND REPLICATION*
Spectral Band Replication, or "SBR", is the most recent tool available in the bit rate reduction arena. Developed by Coding Technologies (
http://www.codingtechnologies.de), this technique works together with a perceptual coder to improve performance by 30%. Therefore, SBR technology will always be seen in the context of another coding scheme. For example, "mp3PRO" is MPEG Layer 3 with the SBR enhancement added. "aacPlus" is Coding Technologies' trademark for their implementation of MPEG AAC (MP4) with SBR added.