aacPlus

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aacPlus

An enhanced AAC audio format from Dolby Laboratories that delivers near CD-quality sound in as little as 32 Kbps. aacPlus extends Low Complexity AAC (AAC LC). Also known as "High Efficiency AAC" (HE-AAC), aacPlus was originally developed by Stockholm-based Coding Technologies, which Dolby acquired in 2007. See AAC and MP3.


HE-AAC version 1 - AAC+
HE-AAC v1 (AAC+) uses Coding Technologies' Spectral Band Replication (SBR) to cut the sampling rate in half. SBR then encodes the missing high frequencies at 1.5 Kbps and stores them in the auxiliary data fields. The decoder restores the high frequencies from the SBR data. See mp3PRO.







HE-AAC version 2 - Enhanced AAC+ (eAAC+)
HE-AAC v2 (eAAC+) uses Parametric Stereo (PS), which combines the left and right channels into a monaural signal. PS encodes the differences between channels as parametric data at 3 Kbps, which is used to decode the monaural stream back into stereo.
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HE-AAC offers the flexibility to encode up to 48 audio channels in various configurations including mono, stereo, 5.
HE-AAC is the mandatory audio codec in DASH-AVC/264, the only native multichannel codec in Android and has been deployed in over 5 Billion CE devices.
It includes intelligent audio analysis and an automated loudness normalization engine, along with the ability to encode, decode, convert, or transcode between the following Dolby formats: Dolby Digital, Dolby Digital Plus, Dolby Pulse, and Dolby E bitstreams, as well as PCM, MPEG-1 LII, AAC, HE-AAC, and HE-AAC v2.
Most codecs are pretty benign these days--AAC at 224Kbps compared to what we've been used to is pretty spectacular, and the HE-AAC data rate can be lower but still maintain the same quality," he says.