aacPlus
An 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. aacPlus Version 1, also known as "High Efficiency AAC Version 1" (HE- AAC v1), uses Spectral Band Replication (SBR), 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).
Used for stereo signals, aacPlus Version 2 (HE-AAC v2) 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.
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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. |