From a strict point of view, the G.723 formerly referred to a standard of codec audio of type ADPCM. This standard was very little implemented and is today obsolete. Unfortunately the standardizing organization had the bad idea to re-use a very similar terminology, G.723.1, to indicate another standard of codec audio infinitely more popular, of type Vocodeur. Today still confusion reigns and the G.723 denomination indicates in the jargon running what should be called G.723.1. The continuation of this article follows the everyday usage and the term G.723 indicates the standard ITU-T G.723.1 .

codec G.723 is before a whole coder of voice. Its algorithm makes the assumption that the treated signal corresponds to a Western human voice. In particular, it appears of poor quality for the coding of nonvocal signals (music,…).

G.723 is standardized for two compression ratios, namely 5.3 kbit/s and 6.4 kbit/s. These two flows correspond to two different types of coding, it is not a question of a simple adjustment. The version with 6.4 kbit/s is of a quality slightly higher than the version 5.3 kbit/s: note MOS of the 6.4 kbit/s reaches 3.9, against 3.65 for the 5.3 kbit/s. These two codecs have 30 ms an algorithmic latency.

Standard ITU-T G.723.1 is equipped with an appendix which defines a behavior different from the codec when a silence is detected. This additional algorithm is called VAD/CNG ( voice activity detection/comfort noise generation, or detection of activity/noise of comfort). In this case only the background noise is modelled and makes it possible to reach an extremely low flow (1 byte every 30 ms) while restoring sound environment. By taking of account percentage of the time when the voice is inactive in a typical conversation, G.723 with VAD/CNG led to a typical medium flow of about 3.5 ~ 3.8 kbit/s.

G.723 is especially used for the videoconference and telephony on IP (VoIP), that it is on indication H.323, H.320 or SIP.

Audio compression G.723 is exceeded today, in terms of acoustic quality and compression ratio. Others codecs profited from advanced in mathematics and average data processing which make it possible to improve the compromise quality/flow. One of the reasons of the perenniality of G.723 remains the constraint of compatibility and interworking with the existing equipment. Another aspect militant in his favor is his relative algorithmic simplicity which enables him to enter telephone terminals (IP) at very low cost where the computing power is limited.

See: Data compression, codec, Streaming.