06.613GPPSubstitution and muting of lost frames for encanced full rate speech traffic channelsTS
5.1 Error detection
An error is detected and the BFI-flag is set-by the RSS according to the principle described in clause 4.
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 will gradually decrease the output level, resulting in silencing of the output. Clause 6.1 gives an example solution.
5.3 First lost SID frame
A single lost SID frame shall be substituted by the last valid SID frame and the procedure for valid SID frames be applied as described in GSM 06.81 .
5.4 Subsequent lost SID frames
For the second lost SID frame, a muting technique shall be used on the comfort noise that will gradually decrease the output level (‑3 dB/frame), resulting in silencing of the output of the decoder.
For subsequent lost SID frames, the muting of the output shall be maintained. Clause 6.2 gives an example solution.