6 Example solution

06.113GPPSubstitution and muting of lost frames for full rate speech channelsTS

For guidance, an example solution is given.

The first lost speech frame is replaced at the speech decoder input by the previous good speech frame. Normal decoding is then performed.

The muting procedure to be used in the case of subsequent lost speech frames or for comfort noise frames following the second lost SID frame is as follows:

The pseudo‑logarithmic encoded block amplitude Xmaxcr (GSM 06.10 [2]), coded on the interval from 0 to 63, is decreased with a constant value d=4 in each frame, down to the lowest possible value. Consequently, Xmaxcr will be reduced gradually, and the output muted after a maximum of 320 ms. The grid position parameters are chosen randomly between 0 and 3 during this time.

For subsequent unusable frames, after the frame where Xmaxcr reached the lowest possible value, "silence frames" are passed from the RX DTX handler to the speech decoder to guarantee a low output level under all conditions. The silence frame is defined in table 1.

Table 1: Encoded parameters (GSM 06.10) of the silence frame

Log area ratio 1 = 42

Log area ratio 2 = 39

Log area ratio 3 = 21

Log area ratio 4 = 10

Log area ratio 5 = 9

Log area ratio 6 = 4

Log area ratio 7 = 3

Log area ratio 8 = 2

_

LTP gain = 0

LTP lag = 40

Grid position = 1

Block amplitude = 0

RPE pulse no. 1 = 3

RPE pulse no. 2 = 4

RPE pulse no. 3 = 3

RPE pulse no. 4 = 4

RPE pulse no. 5 = 4

‑ repeated for each subsegment

RPE pulse no. 6 = 3

RPE pulse no. 7 = 3

RPE pulse no. 8 = 3

RPE pulse no. 9 = 3

RPE pulse no. 10 = 4

RPE pulse no. 11 = 4

RPE pulse no. 12 = 3

RPE pulse no. 13 = 3 _

Annex A (informative):
Change Request History

Change history

SMG No.

TDoc. No.

CR. No.

Clause affected

New version

Subject/Comments

SMG#07

4.0.4

ETSI Publication

SMG#20

5.0.1

Release 1996 version

SMG#27

6.0.0

Release 1997 version

SMG#28

6.0.1

ETSI Publication

SMG#29

7.0.0

Specification version 6.0.0 upgrade to Release 1998 version 7.0.0

7.0.1

Version update for Publication

SMG#31

8.0.0

Release 1999 version

8.0.1

Update to Version 8.0.1 for Publication