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 for
voice over IP applications, such as on a
local area network where network bandwidth is readily available, 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 bitrate-efficient codecs, such as G.722.1 (Siren7) or G.722.2 (AMR-WB). G.722 has also been widely used by radio broadcasters for sending commentary-grade audio over a single 56 or 64 kbit/s
ISDN B-channel (the
least significant bit is dropped on 56 kb circuits). G.722 works by having the inbound voice signal pass through a digital filter that splits the audio signal into 0 Hz-to-4 kHz and 4 kHz-to-8 kHz audio bands. These sub-bands are then encoded using
sub-band ADPCM. Most of the human voice energy is concentrated in the lower half of the audio band (0–4 kHz), so 48 kbit/s of the bandwidth is dedicated to the lower sub-band and the other 16 kbit/s is allocated to the higher sub-band.
RTP encapsulation G.722 VoIP is typically carried in
RTP payload type 9. Note that
IANA records the clock rate for type 9 G.722 as 8 kHz (instead of 16 kHz), RFC 3551 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 kbit/s, in practice, data is encoded at 64 kbit/s, with bits from the lower sub-band being used to encode auxiliary data. The greater the number of bits allocated to aux data, the lower the bit rate. == Licensing ==