FreeCalypso > hg > gsm-codec-lib
annotate libgsmefr/enc_lag6.c @ 242:f081a6850fb5
libgsmfrp: new refined implementation
The previous implementation exhibited the following defects,
which are now fixed:
1) The last received valid SID was cached forever for the purpose of
handling future invalid SIDs - we could have received some valid
SID ages ago, then lots of speech or NO_DATA, and if we then get
an invalid SID, we would resurrect the last valid SID from ancient
history - a bad design. In our new design, we handle invalid SID
based on the current state, much like BFI.
2) GSM 06.11 spec says clearly that after the second lost SID
(received BFI=1 && TAF=1 in CN state) we need to gradually decrease
the output level, rather than jump directly to emitting silence
frames - we previously failed to implement such logic.
3) Per GSM 06.12 section 5.2, Xmaxc should be the same in all 4 subframes
in a SID frame. What should we do if we receive an otherwise valid
SID frame with different Xmaxc? Our previous approach would
replicate this Xmaxc oddity in every subsequent generated CN frame,
which is rather bad. In our new design, the very first CN frame
(which can be seen as a transformation of the SID frame itself)
retains the original 4 distinct Xmaxc, but all subsequent CN frames
are based on the Xmaxc from the last subframe of the most recent SID.
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Tue, 09 May 2023 05:16:31 +0000 |
parents | f151d6c18b31 |
children |
rev | line source |
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1 /************************************************************************* |
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2 * |
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3 * FUNCTION: Enc_lag6 |
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4 * |
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5 * PURPOSE: Encoding of fractional pitch lag with 1/6 resolution. |
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6 * |
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7 * DESCRIPTION: |
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8 * First and third subframes: |
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9 * -------------------------- |
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10 * The pitch range is divided as follows: |
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11 * 17 3/6 to 94 3/6 resolution 1/6 |
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12 * 95 to 143 resolution 1 |
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13 * |
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14 * The period is encoded with 9 bits. |
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15 * For the range with fractions: |
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16 * index = (T-17)*6 + frac - 3; |
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17 * where T=[17..94] and frac=[-2,-1,0,1,2,3] |
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18 * and for the integer only range |
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19 * index = (T - 95) + 463; where T=[95..143] |
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20 * |
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21 * Second and fourth subframes: |
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22 * ---------------------------- |
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23 * For the 2nd and 4th subframes a resolution of 1/6 is always used, |
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24 * and the search range is relative to the lag in previous subframe. |
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25 * If t0 is the lag in the previous subframe then |
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26 * t_min=t0-5 and t_max=t0+4 and the range is given by |
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27 * (t_min-1) 3/6 to (t_max) 3/6 |
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28 * |
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29 * The period in the 2nd (and 4th) subframe is encoded with 6 bits: |
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30 * index = (T-(t_min-1))*6 + frac - 3; |
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31 * where T=[t_min-1..t_max] and frac=[-2,-1,0,1,2,3] |
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32 * |
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33 * Note that only 61 values are used. If the decoder receives 61, 62, |
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34 * or 63 as the relative pitch index, it means that a transmission |
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35 * error occurred and the pitch from previous subframe should be used. |
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36 * |
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37 *************************************************************************/ |
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38 |
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39 #include "gsm_efr.h" |
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40 #include "typedef.h" |
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41 #include "namespace.h" |
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42 #include "basic_op.h" |
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43 #include "no_count.h" |
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44 #include "codec.h" |
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45 |
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46 Word16 Enc_lag6 ( /* output: Return index of encoding */ |
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47 Word16 T0, /* input : Pitch delay */ |
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48 Word16 *T0_frac, /* in/out: Fractional pitch delay */ |
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49 Word16 *T0_min, /* in/out: Minimum search delay */ |
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50 Word16 *T0_max, /* in/out: Maximum search delay */ |
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51 Word16 pit_min, /* input : Minimum pitch delay */ |
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52 Word16 pit_max, /* input : Maximum pitch delay */ |
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53 Word16 pit_flag /* input : Flag for 1st or 3rd subframe */ |
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54 ) |
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55 { |
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56 Word16 index, i; |
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57 |
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58 test (); |
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59 if (pit_flag == 0) /* if 1st or 3rd subframe */ |
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60 { |
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61 /* encode pitch delay (with fraction) */ |
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62 |
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63 test (); |
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64 if (T0 <= 94) |
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65 { |
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66 /* index = T0*6 - 105 + *T0_frac */ |
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67 i = add (add (T0, T0), T0); |
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68 index = add (sub (add (i, i), 105), *T0_frac); |
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69 } else |
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70 { /* set fraction to 0 for delays > 94 */ |
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71 *T0_frac = 0; move16 (); |
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72 index = add (T0, 368); |
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73 } |
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74 |
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75 /* find T0_min and T0_max for second (or fourth) subframe */ |
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76 |
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77 *T0_min = sub (T0, 5); move16 (); |
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78 test (); |
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79 if (*T0_min < pit_min) |
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80 { |
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81 *T0_min = pit_min; move16 (); |
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82 } |
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83 *T0_max = add (*T0_min, 9); |
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84 test (); |
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85 if (*T0_max > pit_max) |
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86 { |
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87 *T0_max = pit_max; move16 (); |
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88 *T0_min = sub (*T0_max, 9); move16 (); |
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89 } |
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90 } else |
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91 /* if second or fourth subframe */ |
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92 { |
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93 /* index = 6*(T0-*T0_min) + 3 + *T0_frac */ |
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94 i = sub (T0, *T0_min); |
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95 i = add (add (i, i), i); |
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96 index = add (add (add (i, i), 3), *T0_frac); |
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97 } |
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98 |
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99 return index; |
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100 } |