AAC-LD
Encyclopedia
The MPEG-4 Low Delay Audio Coder (aka AAC Low Delay, or AAC-LD) is audio compression
format designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the MPEG-2 Advanced Audio Coding
(AAC) format. It was published in MPEG-4 Audio
Version 2 (ISO/IEC
14496-3:1999/Amd 1:2000) and in its later revisions.
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 - 64Kb/s or higher. 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.
Audio compression
Audio compression may refer to:*Audio compression , a type of lossy compression in which the amount of data in a recorded waveform is reduced for transmission with some loss of quality, used in CD and MP3 encoding, Internet radio, and the like...
format designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the MPEG-2 Advanced Audio Coding
Advanced Audio Coding
Advanced Audio Coding is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates....
(AAC) format. It was published in MPEG-4 Audio
MPEG-4 Part 3
MPEG-4 Part 3 or MPEG-4 Audio is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods...
Version 2 (ISO/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
14496-3:1999/Amd 1:2000) and in its later revisions.
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 - 64Kb/s or higher. 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
- Advanced Audio CodingAdvanced Audio CodingAdvanced Audio Coding is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates....
(parent technology) - CELTCELTConstrained Energy Lapped Transform is an open, royalty-free audio compression format and a free software codec with especially low algorithmic delay for use in low-latency audio communication. It is a lossy codec, meaning quality is permanently degraded to reduce file size.The algorithms are...
an alternative codec for similar applications with lower delay and no licensing costs - MP3MP3MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
(related older technology) - G.729G.729G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction .Because of its low bandwidth requirements,...
(ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
's teleconferencing audio codec) - Ultra Low Delay Audio CoderUltra Low Delay Audio CoderThe Ultra Low Delay Audio Coder is a development of the Fraunhofer Institute for Digital Media Technology , which is headed by one of the fathers of MP3, Karlheinz Brandenburg, and of the Fraunhofer Institute for Integrated Circuits...
ULD Audio codec (alternative technology also developed by Fraunhofer)