06.913GPPSubstitution and muting of lost frames for AMR speech traffic channelsTS
5.1 Error detection
An error is detected and the BFI flag is set by the RSS.. The PDFI flag is set appropriately using the soft output from the channel decoder.
5.2 Lost speech frames
Normal decoding of lost speech frames would result in very unpleasant noise effects. In order to improve the subjective quality, lost speech frames shall be substituted with either a repetition or an extrapolation of the previous good speech frame(s). This substitution is done so that it gradually will decrease the output level, resulting in silence at the output. Subclauses 6, and 7 provide example solutions.
5.3 First lost SID frame
A lost SID frame shall be substituted by using the SID information from earlier received valid SID frames and the procedure for valid SID frames be applied as described in GSM 06.93 .
5.4 Subsequent lost SID frames
For many subsequent lost SID frames, a muting technique shall be applied to the comfort noise that will gradually decrease the output level. For subsequent lost SID frames, the muting of the output shall be maintained. Subclauses 6 and 7 provide example solutions.