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(Advanced Audio Coding) An audio compression technology that is part of the MPEG-2 and MPEG-4 standards. AAC, especially MPEG-4 AAC, provides greater compression and better sound quality than MP3, which also came out of the MPEG standard.

Popularized by the iPod
AAC is the default format for Apple's iPod. It was chosen because it improved sound quality and also supported copy protection, which was administered through Apple's iTunes software. AAC song files purchased from the iTunes online store were sold with copy protection, but Apple dropped it in 2009 (see FairPlay). With iTunes, users may also choose to rip their CDs to AAC instead of MP3.

AAC is available in profiles, which determine how the algorithms work to encode the audio data. Main offers the highest quality. Low Complexity (LC) is lower quality, but uses less CPU processing. Scalable Sampling Rate (SSR) is a variation of LC. Long Term Prediction was added in MPEG-4 to improve the Main profile. See aacPlus, Apple Lossless, MP3 and iPod. Following are the file extensions used for AAC:

AAC File Extension   Type of AAC File

     MP4   Standard MPEG-4 video & audio

     M4A   Unprotected AAC
     M4A   Apple Lossless

     M4P   Protected AAC
     M4B   Protected AAC audiobook
References in periodicals archive ?
The commitment and competence of the communication partner will determine the success of any AAC intervention.
The most visible results we've seen at the AAC relate to cross-pollination of various disciplines.
With full-feedback option selected, whenever the user makes a manual sign, chooses a graphic sign, or says a word, HAPPY automatically reproduces it using all the AAC systems implemented.
ATSC M/H encoders may also use Fraunhofer Audio Metadata software to encode AAC metadata parameters directly or from Dolby E sources.
AAC is used by people with a large variety of disabilities.
If you hold shares in AAC, MSLP or HIL and would like to obtain additional information about your legal rights and protect your investment, please visit our website or contact the attorneys below.
Under-20 Men: 60m FINAL: 1 Chris HOWE Cardiff AAC 6.
The purpose of this policy letter is to provide guidance on the professional development of AAC officers--primarily captains and majors.
Ambac" or "AFG") (NYSE: ABK), from fraudulently accepting dividend payments from AAC and utilizing AAC's net operating losses without fair consideration being paid to AAC.
21, 2015 /PRNewswire/ -- Ryan & Maniskas, LLP has commenced an investigation into potential securities law violations by certain officers of AAC Holdings, Inc.
AAC and its associate units share the largest personnel deployment tasking of any Air Force base.