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130 lines
3.5 KiB
C
130 lines
3.5 KiB
C
/******************************************************************************
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*
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* Copyright 2022 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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******************************************************************************/
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#include "bwdet.h"
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/**
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* Bandwidth detector
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*/
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enum lc3_bandwidth lc3_bwdet_run(
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enum lc3_dt dt, enum lc3_srate sr, const float *e)
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{
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/* Bandwidth regions (Table 3.6) */
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struct region { int is : 8; int ie : 8; };
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static const struct region bws_table[LC3_NUM_DT]
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[LC3_NUM_BANDWIDTH-1][LC3_NUM_BANDWIDTH-1] = {
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[LC3_DT_7M5] = {
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{ { 51, 63+1 } },
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{ { 45, 55+1 }, { 58, 63+1 } },
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{ { 42, 51+1 }, { 53, 58+1 }, { 60, 63+1 } },
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{ { 40, 48+1 }, { 51, 55+1 }, { 57, 60+1 }, { 61, 63+1 } },
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},
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[LC3_DT_10M] = {
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{ { 53, 63+1 } },
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{ { 47, 56+1 }, { 59, 63+1 } },
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{ { 44, 52+1 }, { 54, 59+1 }, { 60, 63+1 } },
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{ { 41, 49+1 }, { 51, 55+1 }, { 57, 60+1 }, { 61, 63+1 } },
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},
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};
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static const int l_table[LC3_NUM_DT][LC3_NUM_BANDWIDTH-1] = {
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[LC3_DT_7M5] = { 4, 4, 3, 2 },
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[LC3_DT_10M] = { 4, 4, 3, 1 },
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};
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/* --- Stage 1 ---
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* Determine bw0 candidate */
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enum lc3_bandwidth bw0 = LC3_BANDWIDTH_NB;
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enum lc3_bandwidth bwn = (enum lc3_bandwidth)sr;
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if (bwn <= bw0)
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return bwn;
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const struct region *bwr = bws_table[dt][bwn-1];
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for (enum lc3_bandwidth bw = bw0; bw < bwn; bw++) {
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int i = bwr[bw].is, ie = bwr[bw].ie;
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int n = ie - i;
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float se = e[i];
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for (i++; i < ie; i++)
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se += e[i];
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if (se >= (10 << (bw == LC3_BANDWIDTH_NB)) * n)
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bw0 = bw + 1;
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}
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/* --- Stage 2 ---
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* Detect drop above cut-off frequency.
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* The Tc condition (13) is precalculated, as
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* Tc[] = 10 ^ (n / 10) , n = { 15, 23, 20, 20 } */
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int hold = bw0 >= bwn;
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if (!hold) {
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int i0 = bwr[bw0].is, l = l_table[dt][bw0];
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float tc = (const float []){
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31.62277660, 199.52623150, 100, 100 }[bw0];
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for (int i = i0 - l + 1; !hold && i <= i0 + 1; i++) {
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hold = e[i-l] > tc * e[i];
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}
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}
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return hold ? bw0 : bwn;
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}
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/**
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* Return number of bits coding the bandwidth value
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*/
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int lc3_bwdet_get_nbits(enum lc3_srate sr)
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{
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return (sr > 0) + (sr > 1) + (sr > 3);
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}
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/**
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* Put bandwidth indication
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*/
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void lc3_bwdet_put_bw(lc3_bits_t *bits,
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enum lc3_srate sr, enum lc3_bandwidth bw)
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{
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int nbits_bw = lc3_bwdet_get_nbits(sr);
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if (nbits_bw > 0)
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lc3_put_bits(bits, bw, nbits_bw);
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}
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/**
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* Get bandwidth indication
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*/
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int lc3_bwdet_get_bw(lc3_bits_t *bits,
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enum lc3_srate sr, enum lc3_bandwidth *bw)
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{
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enum lc3_bandwidth max_bw = (enum lc3_bandwidth)sr;
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int nbits_bw = lc3_bwdet_get_nbits(sr);
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*bw = nbits_bw > 0 ? lc3_get_bits(bits, nbits_bw) : LC3_BANDWIDTH_NB;
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return *bw > max_bw ? (*bw = max_bw), -1 : 0;
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}
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