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aacPlusAn enhanced AAC format from Coding Technologies (www.codingtechnologies.com) that extends Low Complexity AAC (AAC LC) to deliver near CD-quality sound in as little as 32 Kbps. Also known as "High Efficiency AAC" (HE-AAC).
Version 1 - AAC+ (HE-AAC v1)
Using Spectral Band Replication (SBR), AAC+ is a proprietary 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).
Version 2 - eAAC+ (HE-AAC v2)
Used for stereo signals, eAAC+ supports Parametric Stereo (PS), which works similar to SBR. PS 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.
|Spectral Band Replication (SBR)|
|SBR encodes the high frequencies and stores them in the auxiliary data fields. The decoder restores the high frequencies from the SBR data.|
|Parametric Stereo (PS)|
|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.|