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Title: Aac-ld  
Author: World Heritage Encyclopedia
Language: English
Subject: H.323, MPEG, Tandberg E20, Polycom, Comparison of audio coding formats
Collection: Audio Codecs, Computer File Formats, Lossy Compression Algorithms, Mpeg, Open Standards Covered by Patents
Publisher: World Heritage Encyclopedia


The MPEG-4 Low Delay Audio Coder (aka AAC Low Delay, or AAC-LD) is ISO/IEC 14496-3:1999/Amd 1:2000)[1][2][3][4][5] and in its later revisions.[6][7]

Real time CODEC requirements

The most stringent requirements are a maximum algorithmic delay of only 20 ms and a good audio quality for all kind of audio signals including speech and music.

  • The AAC-LD coding scheme bridges the gap between speech coding schemes and high quality audio coding schemes.

Two-way communication with AAC-LD is possible on usual analog telephone lines and via ISDN connections. It can use a bit rate of 32 - 64kbit/s or higher.[8] Compared to known speech coders, the codec is capable of coding both music and speech signals with good quality. Unlike speech coders, however, the achieved coding quality scales up with bitrate. Transparent quality can be achieved.

AAC LD can also process stereo signals by using the advanced stereo coding tools of AAC. Thus it is possible to transmit a stereo signal with a bandwidth of 7 kHz via one ISDN line or with a bandwidth of 15 kHz via two ISDN lines.

See also


  1. ^  
  2. ^  
  3. ^ Heiko Purnhagen (2000-02-19). "AES 108th Convention: MPEG-4 Version 2 Audio ­ What is it about?". Heiko Purnhagen. Retrieved 2009-10-07. 
  4. ^ Jurgen Herre,  
  5. ^ Heiko Purnhagen (2001-11-07). "The MPEG Audio Web Page - MPEG-4 Audio (ISO/IEC 14496-3)". Retrieved 2009-10-07. 
  6. ^  
  7. ^  
  8. ^
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