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 "energy.h" 20 #include "tables.h" 21 22 23 /** 24 * Energy estimation per band 25 */ 26 bool lc3_energy_compute( 27 enum lc3_dt dt, enum lc3_srate sr, const float *x, float *e) 28 { 29 static const int n1_table[LC3_NUM_DT][LC3_NUM_SRATE] = { 30 [LC3_DT_7M5] = { 56, 34, 27, 24, 22 }, 31 [LC3_DT_10M] = { 49, 28, 23, 20, 18 }, 32 }; 33 34 /* First bands are 1 coefficient width */ 35 36 int n1 = n1_table[dt][sr]; 37 float e_sum[2] = { 0, 0 }; 38 int iband; 39 40 for (iband = 0; iband < n1; iband++) { 41 *e = x[iband] * x[iband]; 42 e_sum[0] += *(e++); 43 } 44 45 /* Mean the square of coefficients within each band, 46 * note that 7.5ms 8KHz frame has more bands than samples */ 47 48 int nb = LC3_MIN(LC3_NUM_BANDS, LC3_NS(dt, sr)); 49 int iband_h = nb - 2*(2 - dt); 50 const int *lim = lc3_band_lim[dt][sr]; 51 52 for (int i = lim[iband]; iband < nb; iband++) { 53 int ie = lim[iband+1]; 54 int n = ie - i; 55 56 float sx2 = x[i] * x[i]; 57 for (i++; i < ie; i++) 58 sx2 += x[i] * x[i]; 59 60 *e = sx2 / n; 61 e_sum[iband >= iband_h] += *(e++); 62 } 63 64 for (; iband < LC3_NUM_BANDS; iband++) 65 *(e++) = 0; 66 67 /* Return the near nyquist flag */ 68 69 return e_sum[1] > 30 * e_sum[0]; 70 } 71