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