Recommendation ITU-T G.718 describes a narrow‑band (NB) and wideband (WB) embedded variable bit-rate coding algorithm for speech and audio operating in the range from 8 to 32 kbit/s which is designed to be robust to frame erasures.

This codec provides state-of-the-art NB speech quality over the lower bit rates and state-of-the-art WB speech quality over the complete range of bit rates. In addition, the ITU-T G.718 codec is designed to be highly robust to frame erasures, thereby enhancing the speech quality when used in IP transport applications on fixed, wireless and mobile networks. Despite its embedded nature, the codec also performs well with both NB and WB generic audio signals.

This codec has an embedded scalable structure, enabling maximum flexibility in the transport of voice packets through IP networks of today and in future media-aware networks. In addition, the embedded structure of ITU-T G.718 will easily allow the codec to be extended to provide a super‑wideband and stereo capability through additional layers which are currently under development. The bitstream may be truncated at the decoder side or by any component of the communication system to instantaneously adjust the bit rate to the desired value without the need for out-of-band signalling. The encoder produces an embedded bitstream structured in five layers corresponding to the five available bit rates: 8, 12, 16, 24 and 32 kbit/s.

The ITU-T G.718 encoder can accept WB sampled signals at 16 kHz, or NB signals sampled at either 16 or 8 kHz. Similarly, the decoder output can be 16 kHz WB, in addition to 16 or 8 kHz NB. Input signals sampled at 16 kHz, but with bandwidth limited to NB, are detected by the encoder.

The output of the ITU-T G.718 codec is capable of operating with a bandwidth of 300-3400 Hz at 8 and 12 kbit/s and 50-7000 Hz from 8 to 32 kbit/s.

The high quality codec core represents a significant performance improvement, providing 8 kbit/s wideband clean speech quality equivalent to the ITU-T G.722.2 codec at 12.65 kbit/s whilst the 8 kbit/s narrow‑band codec operating mode provides clean speech quality equivalent to the ITU‑T G.729E codec at 11.8 kbit/s.

The codec operates on 20‑ms frames and has a maximum algorithmic delay of 42.875 ms for wideband input and wideband output signals. The maximum algorithmic delay for narrow‑band input and narrow‑band output signals is 43.875 ms. The codec may also be employed in a low-delay mode when the encoder and decoder maximum bit rates are set to 8 kbit/s or 12 kbit/s. In this case, the maximum algorithmic delay is reduced by 10 ms.