Manual

G.722

This is a well known 7 kHz (medium delity) algorithm used in some VOIP telephones and codecs. It is provided for

compability purposes, but is not considered a superior algorithm for audio codecs.

AAC

This algorithm is a highly regarded standard for compressing audio to crical listening standards. It has been judged to

produce “near transparent” audio at a coding rate of 128 kb/s stereo. The standard is a collaborave of several audio

companies’ best eorts, and has become popular as the default audio codec of the Apple™ iTunes™ program. AAC

should be considered the highest quality codec in NX; enhancements like HE-AAC and AAC-ELD aempt to maintain a

similar quality and reduced bandwidth and delay.

HE-AAC

This is a newer version of AAC dened for increased eciency. 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 Replicaon (SBR), a technique that parally synthesizes these high frequencies. HE-AAC is trademarked by other

companies as AACPlus™. HE-AAC (and close derivaves) are oen used as the main audio codec for digital radio and

satellite networks.

HE-AACV2

This algorithm further increases the eciency of HE-AAC by adding intensity 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.

AAC-LD

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 exhibits very low delay (100 mS).

This choice is best when reasonable network throughput is assured, near-transparent audio is required, and interacvity

is needed.

AAC-ELD

This latest algorithm is a combinaon of the LD and HE-AAC variants. It provides the network-conserving benets of SBR

along with the dramacally reduced delay me of LD. For low delay applicaons, it’s usually the best choice.