ACCESS Product Manual
81
G.722- This is a well known 7KHz (medium fidelity) algorithm used in
some VOIP telephones and codecs. It is provided for compatibility purpos-
es, but is not considered a superior algorithm for audio codecs.
This algorithm is a highly regarded standard for compressing audio to
critical listening standards. It has been judged to produce “near transpar-
ent” audio at a coding rate of 128 kbps stereo. The standard is a collabora-
tive of several audio companies best efforts, and has become popular as
the default audio codec of the Apple™ iTunes™ program. AAC should
be considered the highest quality codec in ACCESS—Enhancements like
HE-AAC and AAC-ELD attempt to maintain a similar quality and reduced
bandwidth and delay.
This is a newer version of AAC defined for increased efficiency. The goal of
the algorithm is to produce AAC comparable quality at a lower bit rate. It
does this by encoding lower frequencies to AAC, and higher frequencies
using Spectral Band Replication (SBR), a technique that partially synthe-
sizes these high frequencies. HE-AAC is trademarked by other companies
as AACPlus™. HE-AAC (and close derivatives) are often used as the main
audio codec for digital radio and satellite networks.
This algorithm further increases the efficiency of HE-AAC by adding inten-
sity stereo coding. This results in a lower bit rate for stereo signals. We
also cluster a very reduced rate HE-AAC mono into this category, although
technically it does not contain v2 coding.
This algorithm is an extension of AAC developed by the FhG IIS, who are
the contributors to AAC and primary inventors of the MP3 algorithm. It’s
quality is superior to MP3 at similar bitrates (64-128 kbps) but it exhib-
its very low delay (100mS). This choice is best when reasonable network
throughput is assured, near-transparent audio is required and interactivity
is needed.
This latest algorithm is a combination of the LD and HE AAC variants. It
provides the network conserving benefits of SBR along with the dramati-
cally reduced delay time of LD. For low delay applications, it’s usually the
best choice.
g.722
AAc
he-AAc
he-AAc
v
2
AAc-ld
AAc-eld