G.722

G.722 [ [http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-G.722 ITU-T G.722 page] ITU-T Recommendation G.722 (11/88), "7 kHz audio-coding within 64 kbit/s"] is a ITU-T standard wideband speech codec operating at 48, 56 and 64 kbit/s. Technology of the codec is based on split band ADPCM.

G.722.1 offers lower bit-rate compressions. A more recent variant, G.722.2, also known as AMR-WB ("Adaptive Multirate Wideband"), offers even lower bit-rate compressions, as well as the ability to quickly adapt to varying compressions as the network topography mutates. In the latter case, bandwidth is automatically conserved when network congestion is high. When congestion returns to a normal level, a lower-compression, higher-quality bitrate is restored.

G.722 and its variants sample audio data at a rate of 16 kHz, double that of traditional telephony interfaces, which results in superior audio quality and clarity.

Applications

G.722 is an ITU standard codec that provides 7 kHz wideband audio at data rates from 48, 56 and 64 kbit/s. This is useful in fixed network voice over IP applications, where the required bandwidth is typically not prohibitive, and offers a significant improvement in speech quality over older narrowband codecs such as G.711, without an excessive increase in implementation complexity. Environments where bandwidth is more constrained may prefer one of the more bit-efficient codecs, such as G.722.1 (Siren7) or G.722.2 (AMR-WB).

RTP Encapsulation

G.722 VoIP is typically carried in RTP payload type 9 [ [http://www.iana.org/assignments/rtp-parameters IANA: Authoritative repository for RTP Parameters] ] . Note that IANA records the clock rate for type 9 G.722 as 8kHz (instead of 16kHz), RFC3551 [ [http://tools.ietf.org/html/rfc3551 RFC 3551] Request For Comments 3551: RTP Profile for Audio and Video Conferences with Minimal Control. Schulzrinne & Casener, July 2003. Also Internet Standard 65.] clarifies that this is due to a historical error and is retained in order to maintain backward compatibility. Consequently correct implementations represent the value 8,000 where required but encode and decode audio at 16 kHz.

Whilst G.722 allows for bitrates of 64, 56 and 48 and kbit/s, in practice, data is encoded at 64 kbit/s, with bits from the lower sub-band being used to encode auxiluary data. The greater the number of bits allocated to aux data, the lower the bit rate.

Licensing

G.722 patents have expired, so it is freely available.

[http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.722-198811-I!!PDF-E&type=items G722 specification]

See also

*G.711 (a-law and mu-law/u-law)
*G.718
*G.719
*G.722.1
*G.722.2
*G.723
*G.723.1
*G.726
*G.728
*G.729
*G.729a
* List of codecs

References