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 */ 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 */ 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 */ 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 */ 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