4 General

26.0913GPPAdaptive Multi-Rate (AMR) speech codecError concealment of lost framesMandatory speech CODEC speech processing functionsRelease 17TS

The purpose of the error concealment procedure is to conceal the effect of lost AMR speech frames. The purpose of muting the output in the case of several lost frames is to indicate the breakdown of the channel to the user and to avoid generating possible annoying sounds as a result from the error concealment procedure.

The network shall indicate lost speech or lost SID frames by setting the RX_TYPE values [3] to SPEECH_BAD or SID_BAD. If these flags are set, the speech decoder shall perform parameter substitution to conceal errors.

The network should also indicate potentially degraded frames using the flag RX_TYPE value SPEECH_PROBABLY_DEGRADED. This flag may be derived from channel quality indicators. It may be used by the speech decoder selectively depending on the estimated signal type.

The example solutions provided in paragraphs 6 and 7 apply only to bad frame handling on a complete speech frame basis. Sub-frame based error concealment may be derived using similar methods.