aacPlus
An enhanced AAC format from Coding Technologies (www.codingtechnologies.com) that delivers near CD-quality sound in as little as 32 Kbps. aacPlus Version 1 uses Spectral Band Replication (SBR), a proprietary Coding Technologies' technique that halves the sampling rate, but encodes the missing higher frequencies at a rate of 1.5 Kbps and stores them in the auxiliary data fields of the MPEG format. SBR is also used in the mp3PRO format (see mp3PRO).
aacPlus Version 2 adds Parametric Stereo (PS), which works in a similar fashion to SBR. It encodes the differences between left and right channels as a 3 Kbps data stream that it sends along with the monaural representation of the channels. See AAC and MP3.
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| Spectral Band Replication (SBR) |
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| SBR encodes the high frequencies and stores them in the auxiliary data fields. The decoder restores the high frequencies from the SBR data. |
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| Parametric Stereo (PS) |
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| Parametric Stereo combines the left and right channels into a monaural signal and encodes the differences between channels as parametric data at a bit rate up to 3Kbps. The decoder turns the monaural stream back into stereo from the parametric data. |