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https://github.com/bluekitchen/btstack.git
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458 lines
12 KiB
C
458 lines
12 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 "tns.h"
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#include "tables.h"
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/* ----------------------------------------------------------------------------
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* Filter Coefficients
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* -------------------------------------------------------------------------- */
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/**
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* Resolve LPC Weighting indication according bitrate
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* dt, nbytes Duration and size of the frame
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* return True when LPC Weighting enabled
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*/
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static bool resolve_lpc_weighting(enum lc3_dt dt, int nbytes)
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{
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return nbytes < (dt == LC3_DT_7M5 ? 360/8 : 480/8);
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}
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/**
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* Return dot product of 2 vectors
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* a, b, n The 2 vectors of size `n`
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* return sum( a[i] * b[i] ), i = [0..n-1]
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*/
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LC3_HOT static inline float dot(const float *a, const float *b, int n)
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{
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float v = 0;
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while (n--)
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v += *(a++) * *(b++);
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return v;
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}
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/**
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* LPC Coefficients
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* dt, bw Duration and bandwidth of the frame
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* x Spectral coefficients
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* gain, a Output the prediction gains and LPC coefficients
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*/
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LC3_HOT static void compute_lpc_coeffs(
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enum lc3_dt dt, enum lc3_bandwidth bw,
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const float *x, float *gain, float (*a)[9])
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{
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static const int sub_7m5_nb[] = { 9, 26, 43, 60 };
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static const int sub_7m5_wb[] = { 9, 46, 83, 120 };
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static const int sub_7m5_sswb[] = { 9, 66, 123, 180 };
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static const int sub_7m5_swb[] = { 9, 46, 82, 120, 159, 200, 240 };
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static const int sub_7m5_fb[] = { 9, 56, 103, 150, 200, 250, 300 };
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static const int sub_10m_nb[] = { 12, 34, 57, 80 };
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static const int sub_10m_wb[] = { 12, 61, 110, 160 };
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static const int sub_10m_sswb[] = { 12, 88, 164, 240 };
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static const int sub_10m_swb[] = { 12, 61, 110, 160, 213, 266, 320 };
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static const int sub_10m_fb[] = { 12, 74, 137, 200, 266, 333, 400 };
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/* --- Normalized autocorrelation --- */
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static const float lag_window[] = {
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1.00000000e+00, 9.98028026e-01, 9.92135406e-01, 9.82391584e-01,
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9.68910791e-01, 9.51849807e-01, 9.31404933e-01, 9.07808230e-01,
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8.81323137e-01
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};
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const int *sub = (const int * const [LC3_NUM_DT][LC3_NUM_SRATE]){
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{ sub_7m5_nb, sub_7m5_wb, sub_7m5_sswb, sub_7m5_swb, sub_7m5_fb },
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{ sub_10m_nb, sub_10m_wb, sub_10m_sswb, sub_10m_swb, sub_10m_fb },
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}[dt][bw];
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int nfilters = 1 + (bw >= LC3_BANDWIDTH_SWB);
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const float *xs, *xe = x + *sub;
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float r[2][9];
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for (int f = 0; f < nfilters; f++) {
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float c[9][3];
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for (int s = 0; s < 3; s++) {
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xs = xe, xe = x + *(++sub);
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for (int k = 0; k < 9; k++)
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c[k][s] = dot(xs, xs + k, (xe - xs) - k);
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}
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float e0 = c[0][0], e1 = c[0][1], e2 = c[0][2];
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r[f][0] = 3;
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for (int k = 1; k < 9; k++)
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r[f][k] = e0 == 0 || e1 == 0 || e2 == 0 ? 0 :
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(c[k][0]/e0 + c[k][1]/e1 + c[k][2]/e2) * lag_window[k];
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}
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/* --- Levinson-Durbin recursion --- */
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for (int f = 0; f < nfilters; f++) {
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float *a0 = a[f], a1[9];
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float err = r[f][0], rc;
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gain[f] = err;
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a0[0] = 1;
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for (int k = 1; k < 9; ) {
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rc = -r[f][k];
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for (int i = 1; i < k; i++)
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rc -= a0[i] * r[f][k-i];
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rc /= err;
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err *= 1 - rc * rc;
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for (int i = 1; i < k; i++)
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a1[i] = a0[i] + rc * a0[k-i];
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a1[k++] = rc;
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rc = -r[f][k];
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for (int i = 1; i < k; i++)
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rc -= a1[i] * r[f][k-i];
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rc /= err;
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err *= 1 - rc * rc;
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for (int i = 1; i < k; i++)
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a0[i] = a1[i] + rc * a1[k-i];
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a0[k++] = rc;
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}
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gain[f] /= err;
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}
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}
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/**
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* LPC Weighting
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* gain, a Prediction gain and LPC coefficients, weighted as output
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*/
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LC3_HOT static void lpc_weighting(float pred_gain, float *a)
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{
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float gamma = 1.f - (1.f - 0.85f) * (2.f - pred_gain) / (2.f - 1.5f);
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float g = 1.f;
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for (int i = 1; i < 9; i++)
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a[i] *= (g *= gamma);
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}
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/**
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* LPC reflection
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* a LPC coefficients
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* rc Output refelection coefficients
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*/
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LC3_HOT static void lpc_reflection(const float *a, float *rc)
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{
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float e, b[2][7], *b0, *b1;
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rc[7] = a[1+7];
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e = 1 - rc[7] * rc[7];
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b1 = b[1];
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for (int i = 0; i < 7; i++)
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b1[i] = (a[1+i] - rc[7] * a[7-i]) / e;
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for (int k = 6; k > 0; k--) {
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b0 = b1, b1 = b[k & 1];
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rc[k] = b0[k];
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e = 1 - rc[k] * rc[k];
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for (int i = 0; i < k; i++)
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b1[i] = (b0[i] - rc[k] * b0[k-1-i]) / e;
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}
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rc[0] = b1[0];
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}
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/**
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* Quantization of RC coefficients
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* rc Refelection coefficients
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* rc_order Return order of coefficients
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* rc_i Return quantized coefficients
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*/
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static void quantize_rc(const float *rc, int *rc_order, int *rc_q)
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{
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/* Quantization table, sin(delta * (i + 0.5)), delta = Pi / 17 */
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static float q_thr[] = {
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9.22683595e-02, 2.73662990e-01, 4.45738356e-01, 6.02634636e-01,
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7.39008917e-01, 8.50217136e-01, 9.32472229e-01, 9.82973100e-01
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};
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*rc_order = 8;
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for (int i = 0; i < 8; i++) {
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float rc_m = fabsf(rc[i]);
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rc_q[i] = 4 * (rc_m >= q_thr[4]);
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for (int j = 0; j < 4 && rc_m >= q_thr[rc_q[i]]; j++, rc_q[i]++);
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if (rc[i] < 0)
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rc_q[i] = -rc_q[i];
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*rc_order = rc_q[i] != 0 ? 8 : *rc_order - 1;
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}
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}
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/**
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* Unquantization of RC coefficients
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* rc_q Quantized coefficients
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* rc_order Order of coefficients
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* rc Return refelection coefficients
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*/
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static void unquantize_rc(const int *rc_q, int rc_order, float rc[8])
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{
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/* Quantization table, sin(delta * i), delta = Pi / 17 */
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static float q_inv[] = {
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0.00000000e+00, 1.83749517e-01, 3.61241664e-01, 5.26432173e-01,
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6.73695641e-01, 7.98017215e-01, 8.95163302e-01, 9.61825645e-01,
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9.95734176e-01
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};
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int i;
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for (i = 0; i < rc_order; i++) {
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float rc_m = q_inv[LC3_ABS(rc_q[i])];
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rc[i] = rc_q[i] < 0 ? -rc_m : rc_m;
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}
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}
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/* ----------------------------------------------------------------------------
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* Filtering
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* -------------------------------------------------------------------------- */
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/**
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* Forward filtering
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* dt, bw Duration and bandwidth of the frame
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* rc_order, rc Order of coefficients, and coefficients
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* x Spectral coefficients, filtered as output
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*/
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LC3_HOT static void forward_filtering(
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enum lc3_dt dt, enum lc3_bandwidth bw,
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const int rc_order[2], const float rc[2][8], float *x)
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{
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int nfilters = 1 + (bw >= LC3_BANDWIDTH_SWB);
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int nf = LC3_NE(dt, bw) >> (nfilters - 1);
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int i0, ie = 3*(3 + dt);
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float s[8] = { 0 };
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for (int f = 0; f < nfilters; f++) {
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i0 = ie;
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ie = nf * (1 + f);
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if (!rc_order[f])
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continue;
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for (int i = i0; i < ie; i++) {
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float xi = x[i];
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float s0, s1 = xi;
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for (int k = 0; k < rc_order[f]; k++) {
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s0 = s[k];
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s[k] = s1;
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s1 = rc[f][k] * xi + s0;
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xi += rc[f][k] * s0;
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}
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x[i] = xi;
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}
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}
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}
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/**
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* Inverse filtering
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* dt, bw Duration and bandwidth of the frame
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* rc_order, rc Order of coefficients, and unquantized coefficients
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* x Spectral coefficients, filtered as output
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*/
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LC3_HOT static void inverse_filtering(
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enum lc3_dt dt, enum lc3_bandwidth bw,
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const int rc_order[2], const float rc[2][8], float *x)
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{
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int nfilters = 1 + (bw >= LC3_BANDWIDTH_SWB);
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int nf = LC3_NE(dt, bw) >> (nfilters - 1);
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int i0, ie = 3*(3 + dt);
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float s[8] = { 0 };
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for (int f = 0; f < nfilters; f++) {
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i0 = ie;
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ie = nf * (1 + f);
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if (!rc_order[f])
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continue;
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for (int i = i0; i < ie; i++) {
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float xi = x[i];
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xi -= s[7] * rc[f][7];
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for (int k = 6; k >= 0; k--) {
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xi -= s[k] * rc[f][k];
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s[k+1] = s[k] + rc[f][k] * xi;
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}
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s[0] = xi;
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x[i] = xi;
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}
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for (int k = 7; k >= rc_order[f]; k--)
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s[k] = 0;
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}
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}
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/* ----------------------------------------------------------------------------
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* Interface
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* -------------------------------------------------------------------------- */
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/**
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* TNS analysis
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*/
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void lc3_tns_analyze(enum lc3_dt dt, enum lc3_bandwidth bw,
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bool nn_flag, int nbytes, struct lc3_tns_data *data, float *x)
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{
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/* Processing steps :
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* - Determine the LPC (Linear Predictive Coding) Coefficients
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* - Check is the filtering is disabled
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* - The coefficients are weighted on low bitrates and predicition gain
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* - Convert to reflection coefficients and quantize
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* - Finally filter the spectral coefficients */
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float pred_gain[2], a[2][9];
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float rc[2][8];
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data->nfilters = 1 + (bw >= LC3_BANDWIDTH_SWB);
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data->lpc_weighting = resolve_lpc_weighting(dt, nbytes);
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compute_lpc_coeffs(dt, bw, x, pred_gain, a);
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for (int f = 0; f < data->nfilters; f++) {
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data->rc_order[f] = 0;
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if (nn_flag || pred_gain[f] <= 1.5f)
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continue;
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if (data->lpc_weighting && pred_gain[f] < 2.f)
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lpc_weighting(pred_gain[f], a[f]);
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lpc_reflection(a[f], rc[f]);
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quantize_rc(rc[f], &data->rc_order[f], data->rc[f]);
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unquantize_rc(data->rc[f], data->rc_order[f], rc[f]);
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}
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forward_filtering(dt, bw, data->rc_order, rc, x);
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}
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/**
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* TNS synthesis
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*/
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void lc3_tns_synthesize(enum lc3_dt dt, enum lc3_bandwidth bw,
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const struct lc3_tns_data *data, float *x)
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{
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float rc[2][8] = { };
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for (int f = 0; f < data->nfilters; f++)
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if (data->rc_order[f])
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unquantize_rc(data->rc[f], data->rc_order[f], rc[f]);
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inverse_filtering(dt, bw, data->rc_order, rc, x);
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}
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/**
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* Bit consumption of bitstream data
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*/
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int lc3_tns_get_nbits(const struct lc3_tns_data *data)
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{
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int nbits = 0;
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for (int f = 0; f < data->nfilters; f++) {
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int nbits_2048 = 2048;
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int rc_order = data->rc_order[f];
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nbits_2048 += rc_order > 0 ? lc3_tns_order_bits
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[data->lpc_weighting][rc_order-1] : 0;
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for (int i = 0; i < rc_order; i++)
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nbits_2048 += lc3_tns_coeffs_bits[i][8 + data->rc[f][i]];
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nbits += (nbits_2048 + (1 << 11) - 1) >> 11;
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}
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return nbits;
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}
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/**
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* Put bitstream data
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*/
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void lc3_tns_put_data(lc3_bits_t *bits, const struct lc3_tns_data *data)
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{
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for (int f = 0; f < data->nfilters; f++) {
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int rc_order = data->rc_order[f];
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lc3_put_bits(bits, rc_order > 0, 1);
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if (rc_order <= 0)
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continue;
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lc3_put_symbol(bits,
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lc3_tns_order_models + data->lpc_weighting, rc_order-1);
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for (int i = 0; i < rc_order; i++)
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lc3_put_symbol(bits,
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lc3_tns_coeffs_models + i, 8 + data->rc[f][i]);
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}
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}
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/**
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* Get bitstream data
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*/
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void lc3_tns_get_data(lc3_bits_t *bits,
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enum lc3_dt dt, enum lc3_bandwidth bw, int nbytes, lc3_tns_data_t *data)
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{
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data->nfilters = 1 + (bw >= LC3_BANDWIDTH_SWB);
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data->lpc_weighting = resolve_lpc_weighting(dt, nbytes);
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for (int f = 0; f < data->nfilters; f++) {
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data->rc_order[f] = lc3_get_bit(bits);
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if (!data->rc_order[f])
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continue;
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data->rc_order[f] += lc3_get_symbol(bits,
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lc3_tns_order_models + data->lpc_weighting);
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for (int i = 0; i < data->rc_order[f]; i++)
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data->rc[f][i] = (int)lc3_get_symbol(bits,
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lc3_tns_coeffs_models + i) - 8;
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}
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}
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