AAC
Advanced Audio Coding
A general audio coding standard designed as a successor to MP3 that generally offers better sound quality at the same bit rate.
AAC-LC
Advanced Audio Coding – Low Complexity
It is an audio codec used for lossy compression of digital audio. AAC-LC is a specific profile within the AAC standard, known for its good sound quality at low bitrates and relatively low complexity, making it suitable for devices with limited computing power.
HE-AAC
High-Efficiency Advanced Audio Coding
HE-AAC, also known as AAC-plus or AAC-SBR, is a lossy audio compression format that is an enhancement of the Advanced Audio Coding (AAC) standard. It utilizes Spectral Band Replication (SBR) to achieve higher compression efficiency, particularly at lower bitrates, making it suitable for streaming and mobile applications.
Key Features:
- Spectral Band Replication (SBR) : HE-AAC uses SBR to encode high-frequency information separately and reconstruct it at the decoder, effectively reducing the bitrate needed for high-quality audio
- Low Bitrate Performance : It is designed to deliver good audio quality even at lower bitrates (e.g., 32-64 kbps for stereo) compared to other codecs like AAC-LC
- Suitable for Streaming and Mobile : HE-AAC is widely used for streaming music services, internet radio, and digital broadcasting where bandwidth and storage are limited
- Standardized : HE-AAC is standardized as a profile of MPEG-4 Audio
How it Works?
- AAC Encoding: The core audio signal is encoded using the standard AAC-LC (Low Complexity) algorithm
- SBR Encoding: The high-frequency components of the audio are encoded using SBR, which effectively reduces the sampling rate and stores the missing high frequencies in side information
- Decoding: The HE-AAC decoder restores the high frequencies using the SBR data
HE-AAC v2
High-Efficiency Advanced Audio Coding v2
HE-AAC v2 builds upon HE-AAC by adding Parametric Stereo (PS) for stereo signals, further improving compression efficiency, especially at very low bitrates.
Key Features:
- AAC (see above)
- SBR (see above)
- PS (Parametric Stereo): A method of compressing stereo sound by generating additional information about the left and right channels, resulting in efficient stereo compression