|Sampling frequency||16kHz (double ISDN quality)|
The ITU-T guideline G.722 7 kHz audio coding within 64 kbit/s describes the coding of audio signals for transmission over a digital transmission path at 64 kbit/s, for example a B channel of ISDN. G.722 was approved in November 1988. In the meantime, the patents relating to the procedure have expired. G.722 is the de facto standard for HD telephony with VoIP hardware telephones and is used, for example, with VoIP connections from Deutsche Telekom.
G.722 measures the frequency range from 50 Hz to 7000 Hz with a sampling rate of 16 kHz and quantized with 14 bits. The codec therefore has a bandwidth of approximately 7 kHz. An encoder reduces the data transfer rate to 64 kbit/s (Mode 1), 56 kbit/s (Mode 2) or 48 kbit/s (Mode 3). The technology is based on subband ADPCM .
G.722 is currently used particularly for VoIP e.g. in our Snom phones. CAT-iq, the new transmission method for cordless telephones based on the DECT standard, also provides for this codec for broadband voice transmission between base station and handset.
In the Mean Opinion Score (MOS) , G.722 reaches a value of 4.5. The MOS determines the subjective perception of a user's voice quality. G,722 thus achieved the best result at present.