1 /******************************************************************************
2 *
3 * Copyright 2022 Google LLC
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at:
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 ******************************************************************************/
18
19 #include "bwdet.h"
20
21
22 /**
23 * Bandwidth detector
24 */
lc3_bwdet_run(enum lc3_dt dt,enum lc3_srate sr,const float * e)25 enum lc3_bandwidth lc3_bwdet_run(
26 enum lc3_dt dt, enum lc3_srate sr, const float *e)
27 {
28 /* Bandwidth regions (Table 3.6) */
29
30 struct region { int is : 8; int ie : 8; };
31
32 static const struct region bws_table[LC3_NUM_DT]
33 [LC3_NUM_BANDWIDTH-1][LC3_NUM_BANDWIDTH-1] = {
34
35 [LC3_DT_7M5] = {
36 { { 51, 63+1 } },
37 { { 45, 55+1 }, { 58, 63+1 } },
38 { { 42, 51+1 }, { 53, 58+1 }, { 60, 63+1 } },
39 { { 40, 48+1 }, { 51, 55+1 }, { 57, 60+1 }, { 61, 63+1 } },
40 },
41
42 [LC3_DT_10M] = {
43 { { 53, 63+1 } },
44 { { 47, 56+1 }, { 59, 63+1 } },
45 { { 44, 52+1 }, { 54, 59+1 }, { 60, 63+1 } },
46 { { 41, 49+1 }, { 51, 55+1 }, { 57, 60+1 }, { 61, 63+1 } },
47 },
48 };
49
50 static const int l_table[LC3_NUM_DT][LC3_NUM_BANDWIDTH-1] = {
51 [LC3_DT_7M5] = { 4, 4, 3, 2 },
52 [LC3_DT_10M] = { 4, 4, 3, 1 },
53 };
54
55 /* --- Stage 1 ---
56 * Determine bw0 candidate */
57
58 enum lc3_bandwidth bw0 = LC3_BANDWIDTH_NB;
59 enum lc3_bandwidth bwn = (enum lc3_bandwidth)sr;
60
61 if (bwn <= bw0)
62 return bwn;
63
64 const struct region *bwr = bws_table[dt][bwn-1];
65
66 for (enum lc3_bandwidth bw = bw0; bw < bwn; bw++) {
67 int i = bwr[bw].is, ie = bwr[bw].ie;
68 int n = ie - i;
69
70 float se = e[i];
71 for (i++; i < ie; i++)
72 se += e[i];
73
74 if (se >= (10 << (bw == LC3_BANDWIDTH_NB)) * n)
75 bw0 = bw + 1;
76 }
77
78 /* --- Stage 2 ---
79 * Detect drop above cut-off frequency.
80 * The Tc condition (13) is precalculated, as
81 * Tc[] = 10 ^ (n / 10) , n = { 15, 23, 20, 20 } */
82
83 int hold = bw0 >= bwn;
84
85 if (!hold) {
86 int i0 = bwr[bw0].is, l = l_table[dt][bw0];
87 float tc = (const float []){
88 31.62277660, 199.52623150, 100, 100 }[bw0];
89
90 for (int i = i0 - l + 1; !hold && i <= i0 + 1; i++) {
91 hold = e[i-l] > tc * e[i];
92 }
93
94 }
95
96 return hold ? bw0 : bwn;
97 }
98
99 /**
100 * Return number of bits coding the bandwidth value
101 */
lc3_bwdet_get_nbits(enum lc3_srate sr)102 int lc3_bwdet_get_nbits(enum lc3_srate sr)
103 {
104 return (sr > 0) + (sr > 1) + (sr > 3);
105 }
106
107 /**
108 * Put bandwidth indication
109 */
lc3_bwdet_put_bw(lc3_bits_t * bits,enum lc3_srate sr,enum lc3_bandwidth bw)110 void lc3_bwdet_put_bw(lc3_bits_t *bits,
111 enum lc3_srate sr, enum lc3_bandwidth bw)
112 {
113 int nbits_bw = lc3_bwdet_get_nbits(sr);
114 if (nbits_bw > 0)
115 lc3_put_bits(bits, bw, nbits_bw);
116 }
117
118 /**
119 * Get bandwidth indication
120 */
lc3_bwdet_get_bw(lc3_bits_t * bits,enum lc3_srate sr,enum lc3_bandwidth * bw)121 int lc3_bwdet_get_bw(lc3_bits_t *bits,
122 enum lc3_srate sr, enum lc3_bandwidth *bw)
123 {
124 enum lc3_bandwidth max_bw = (enum lc3_bandwidth)sr;
125 int nbits_bw = lc3_bwdet_get_nbits(sr);
126
127 *bw = nbits_bw > 0 ? lc3_get_bits(bits, nbits_bw) : LC3_BANDWIDTH_NB;
128 return *bw > max_bw ? (*bw = max_bw), -1 : 0;
129 }
130
