What is AAC?
Audio Format Description
AAC, or Advanced Audio Coding, is a lossy compression and encoding algorithm for digital audio. Designed by the MPEG group that includes Dolby, Sony, Nokia, FhG, and AT&T, it is believed to be the successor to MP3. AAC was officially declared an international standard in 1997. AAC is often referred to as ‘MP4 audio’ as it is usually packaged inside an MP4 container. AAC is the default audio format for iTunes, iPod, and iPhone.The AAC format gives developers increased flexibility over MP3, thus allowing them to develop parallel encoding strategies which in turn give more efficient compression. The two main coding strategies used, which greatly reduce the amount of data, are discarding of irrelevant signal components, and eliminating redundancies in the coded audio signal. Other strategies include adding of internal error correction codes, processing the signal according to its complexity, and applying of a special algorithm to each frame in order to prevent corrupt samples.
Some of the other advantages of AAC are:
- greater range of sample frequencies (from 8 kHz to 96 kHz)
- better handling of audio frequencies above 16 kHz
- up to 48 channels
- variable frame length and random bitrates
- simpler and more efficient filter bank
- transient (block size: 192 > 128 samples) and stationary (block size: 576 > 1024 samples) signals
- and elimination spectral leakage.
Because of all its advantages, AAC has become widely popular and has replaced MP3 to a great extent. It is today the preferred audio codec for the internet, and the wireless and digital platforms.
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