/******************************************************************************
*
* 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 "tns.h"
#include "tables.h"
/* ----------------------------------------------------------------------------
* Filter Coefficients
* -------------------------------------------------------------------------- */
/**
* Resolve LPC Weighting indication according bitrate
* dt, nbytes Duration and size of the frame
* return True when LPC Weighting enabled
*/
static bool resolve_lpc_weighting(enum lc3_dt dt, int nbytes)
{
return nbytes * 8 < 120 * (int)(1 + dt);
}
/**
* Return dot product of 2 vectors
* a, b, n The 2 vectors of size `n`
* return sum( a[i] * b[i] ), i = [0..n-1]
*/
LC3_HOT static inline float dot(const float *a, const float *b, int n)
{
float v = 0;
while (n--)
v += *(a++) * *(b++);
return v;
}
/**
* LPC Coefficients
* dt, bw Duration and bandwidth of the frame
* maxorder Maximum order of filter
* x Spectral coefficients
* gain, a Output the prediction gains and LPC coefficients
*/
LC3_HOT static void compute_lpc_coeffs(
enum lc3_dt dt, enum lc3_bandwidth bw, int maxorder,
const float *x, float *gain, float (*a)[9])
{
#if LC3_PLUS
static const int sub_2m5_nb[] = { 3, 10, 20 };
static const int sub_2m5_wb[] = { 3, 20, 40 };
static const int sub_2m5_sswb[] = { 3, 30, 60 };
static const int sub_2m5_swb[] = { 3, 40, 80 };
static const int sub_2m5_fb[] = { 3, 51, 100 };
static const int sub_5m_nb[] = { 6, 23, 40 };
static const int sub_5m_wb[] = { 6, 43, 80 };
static const int sub_5m_sswb[] = { 6, 63, 120 };
static const int sub_5m_swb[] = { 6, 43, 80, 120, 160 };
static const int sub_5m_fb[] = { 6, 53, 100, 150, 200 };
#endif /* LC3_PLUS */
static const int sub_7m5_nb[] = { 9, 26, 43, 60 };
static const int sub_7m5_wb[] = { 9, 46, 83, 120 };
static const int sub_7m5_sswb[] = { 9, 66, 123, 180 };
static const int sub_7m5_swb[] = { 9, 46, 82, 120, 159, 200, 240 };
static const int sub_7m5_fb[] = { 9, 56, 103, 150, 200, 250, 300 };
static const int sub_10m_nb[] = { 12, 34, 57, 80 };
static const int sub_10m_wb[] = { 12, 61, 110, 160 };
static const int sub_10m_sswb[] = { 12, 88, 164, 240 };
static const int sub_10m_swb[] = { 12, 61, 110, 160, 213, 266, 320 };
static const int sub_10m_fb[] = { 12, 74, 137, 200, 266, 333, 400 };
static const float lag_window[] = {
1.00000000e+00, 9.98028026e-01, 9.92135406e-01, 9.82391584e-01,
9.68910791e-01, 9.51849807e-01, 9.31404933e-01, 9.07808230e-01,
8.81323137e-01
};
const int *sub = (const int * const [LC3_NUM_DT][LC3_NUM_BANDWIDTH]){
#if LC3_PLUS
[LC3_DT_2M5] = {
sub_2m5_nb, sub_2m5_wb, sub_2m5_sswb, sub_2m5_swb,
sub_2m5_fb, sub_2m5_fb, sub_2m5_fb },
[LC3_DT_5M] = {
sub_5m_nb , sub_5m_wb , sub_5m_sswb , sub_5m_swb ,
sub_5m_fb , sub_5m_fb , sub_5m_fb },
#endif /* LC3_PLUS */
[LC3_DT_7M5] = {
sub_7m5_nb, sub_7m5_wb, sub_7m5_sswb, sub_7m5_swb,
sub_7m5_fb },
[LC3_DT_10M] = {
sub_10m_nb, sub_10m_wb, sub_10m_sswb, sub_10m_swb,
sub_10m_fb, sub_10m_fb, sub_10m_fb },
}[dt][bw];
/* --- Normalized autocorrelation --- */
int nfilters = 1 + (dt >= LC3_DT_5M && bw >= LC3_BANDWIDTH_SWB);
int nsubdivisions = 2 + (dt >= LC3_DT_7M5);
const float *xs, *xe = x + *sub;
float r[2][9];
for (int f = 0; f < nfilters; f++) {
float c[9][3] = { 0 };
for (int s = 0; s < nsubdivisions; s++) {
xs = xe, xe = x + *(++sub);
for (int k = 0; k <= maxorder; k++)
c[k][s] = dot(xs, xs + k, (xe - xs) - k);
}
r[f][0] = nsubdivisions;
if (nsubdivisions == 2) {
float e0 = c[0][0], e1 = c[0][1];
for (int k = 1; k <= maxorder; k++)
r[f][k] = e0 == 0 || e1 == 0 ? 0 :
(c[k][0]/e0 + c[k][1]/e1) * lag_window[k];
} else {
float e0 = c[0][0], e1 = c[0][1], e2 = c[0][2];
for (int k = 1; k <= maxorder; k++)
r[f][k] = e0 == 0 || e1 == 0 || e2 == 0 ? 0 :
(c[k][0]/e0 + c[k][1]/e1 + c[k][2]/e2) * lag_window[k];
}
}
/* --- Levinson-Durbin recursion --- */
for (int f = 0; f < nfilters; f++) {
float *a0 = a[f], a1[9];
float err = r[f][0], rc;
gain[f] = err;
a0[0] = 1;
for (int k = 1; k <= maxorder; ) {
rc = -r[f][k];
for (int i = 1; i < k; i++)
rc -= a0[i] * r[f][k-i];
rc /= err;
err *= 1 - rc * rc;
for (int i = 1; i < k; i++)
a1[i] = a0[i] + rc * a0[k-i];
a1[k++] = rc;
rc = -r[f][k];
for (int i = 1; i < k; i++)
rc -= a1[i] * r[f][k-i];
rc /= err;
err *= 1 - rc * rc;
for (int i = 1; i < k; i++)
a0[i] = a1[i] + rc * a1[k-i];
a0[k++] = rc;
}
gain[f] /= err;
}
}
/**
* LPC Weighting
* gain, a Prediction gain and LPC coefficients, weighted as output
*/
LC3_HOT static void lpc_weighting(float pred_gain, float *a)
{
float gamma = 1.f - (1.f - 0.85f) * (2.f - pred_gain) / (2.f - 1.5f);
float g = 1.f;
for (int i = 1; i < 9; i++)
a[i] *= (g *= gamma);
}
/**
* LPC reflection
* a, maxorder LPC coefficients, and maximum order (4 or 8)
* rc Output refelection coefficients
*/
LC3_HOT static void lpc_reflection(
const float *a, int maxorder, float *rc)
{
float e, b[2][7], *b0, *b1;
rc[maxorder-1] = a[maxorder];
e = 1 - rc[maxorder-1] * rc[maxorder-1];
b1 = b[1];
for (int i = 0; i < maxorder-1; i++)
b1[i] = (a[1+i] - rc[maxorder-1] * a[(maxorder-1)-i]) / e;
for (int k = maxorder-2; k > 0; k--) {
b0 = b1, b1 = b[k & 1];
rc[k] = b0[k];
e = 1 - rc[k] * rc[k];
for (int i = 0; i < k; i++)
b1[i] = (b0[i] - rc[k] * b0[k-1-i]) / e;
}
rc[0] = b1[0];
}
/**
* Quantization of RC coefficients
* rc, maxorder Refelection coefficients, and maximum order (4 or 8)
* order Return order of coefficients
* rc_i Return quantized coefficients
*/
static void quantize_rc(const float *rc, int maxorder, int *order, int *rc_q)
{
/* Quantization table, sin(delta * (i + 0.5)), delta = Pi / 17,
* rounded to fixed point Q15 value (LC3-Plus HR requirements). */
static float q_thr[] = {
0x0bcfp-15, 0x2307p-15, 0x390ep-15, 0x4d23p-15,
0x5e98p-15, 0x6cd4p-15, 0x775bp-15, 0x7dd2p-15,
};
*order = maxorder;
for (int i = 0; i < maxorder; i++) {
float rc_m = fabsf(rc[i]);
rc_q[i] = 4 * (rc_m >= q_thr[4]);
for (int j = 0; j < 4 && rc_m >= q_thr[rc_q[i]]; j++, rc_q[i]++);
if (rc[i] < 0)
rc_q[i] = -rc_q[i];
*order = rc_q[i] != 0 ? maxorder : *order - 1;
}
}
/**
* Unquantization of RC coefficients
* rc_q, order Quantized coefficients, and order
* rc Return refelection coefficients
*/
static void unquantize_rc(const int *rc_q, int order, float rc[8])
{
/* Quantization table, sin(delta * i), delta = Pi / 17,
* rounded to fixed point Q15 value (LC3-Plus HR requirements). */
static float q_inv[] = {
0x0000p-15, 0x1785p-15, 0x2e3dp-15, 0x4362p-15,
0x563cp-15, 0x6625p-15, 0x7295p-15, 0x7b1dp-15, 0x7f74p-15,
};
int i;
for (i = 0; i < order; i++) {
float rc_m = q_inv[LC3_ABS(rc_q[i])];
rc[i] = rc_q[i] < 0 ? -rc_m : rc_m;
}
}
/* ----------------------------------------------------------------------------
* Filtering
* -------------------------------------------------------------------------- */
/**
* Forward filtering
* dt, bw Duration and bandwidth of the frame
* rc_order, rc Order of coefficients, and coefficients
* x Spectral coefficients, filtered as output
*/
LC3_HOT static void forward_filtering(
enum lc3_dt dt, enum lc3_bandwidth bw,
const int rc_order[2], float (* const rc)[8], float *x)
{
int nfilters = 1 + (dt >= LC3_DT_5M && bw >= LC3_BANDWIDTH_SWB);
int nf = lc3_ne(dt, (enum lc3_srate)LC3_MIN(bw, LC3_BANDWIDTH_FB))
>> (nfilters - 1);
int i0, ie = 3*(1 + dt);
float s[8] = { 0 };
for (int f = 0; f < nfilters; f++) {
i0 = ie;
ie = nf * (1 + f);
if (!rc_order[f])
continue;
for (int i = i0; i < ie; i++) {
float xi = x[i];
float s0, s1 = xi;
for (int k = 0; k < rc_order[f]; k++) {
s0 = s[k];
s[k] = s1;
s1 = rc[f][k] * xi + s0;
xi += rc[f][k] * s0;
}
x[i] = xi;
}
}
}
/**
* Inverse filtering
* dt, bw Duration and bandwidth of the frame
* rc_order, rc Order of coefficients, and unquantized coefficients
* x Spectral coefficients, filtered as output
*/
LC3_HOT static void inverse_filtering(
enum lc3_dt dt, enum lc3_bandwidth bw,
const int rc_order[2], float (* const rc)[8], float *x)
{
int nfilters = 1 + (dt >= LC3_DT_5M && bw >= LC3_BANDWIDTH_SWB);
int nf = lc3_ne(dt, (enum lc3_srate)LC3_MIN(bw, LC3_BANDWIDTH_FB))
>> (nfilters - 1);
int i0, ie = 3*(1 + dt);
float s[8] = { 0 };
for (int f = 0; f < nfilters; f++) {
i0 = ie;
ie = nf * (1 + f);
if (!rc_order[f])
continue;
for (int i = i0; i < ie; i++) {
float xi = x[i];
xi -= s[7] * rc[f][7];
for (int k = 6; k >= 0; k--) {
xi -= s[k] * rc[f][k];
s[k+1] = s[k] + rc[f][k] * xi;
}
s[0] = xi;
x[i] = xi;
}
for (int k = 7; k >= rc_order[f]; k--)
s[k] = 0;
}
}
/* ----------------------------------------------------------------------------
* Interface
* -------------------------------------------------------------------------- */
/**
* TNS analysis
*/
void lc3_tns_analyze(enum lc3_dt dt, enum lc3_bandwidth bw,
bool nn_flag, int nbytes, struct lc3_tns_data *data, float *x)
{
/* Processing steps :
* - Determine the LPC (Linear Predictive Coding) Coefficients
* - Check is the filtering is disabled
* - The coefficients are weighted on low bitrates and predicition gain
* - Convert to reflection coefficients and quantize
* - Finally filter the spectral coefficients */
float pred_gain[2], a[2][9];
float rc[2][8];
data->lpc_weighting = resolve_lpc_weighting(dt, nbytes);
data->nfilters = 1 + (dt >= LC3_DT_5M && bw >= LC3_BANDWIDTH_SWB);
int maxorder = dt <= LC3_DT_5M ? 4 : 8;
compute_lpc_coeffs(dt, bw, maxorder, x, pred_gain, a);
for (int f = 0; f < data->nfilters; f++) {
data->rc_order[f] = 0;
if (nn_flag || pred_gain[f] <= 1.5f)
continue;
if (data->lpc_weighting && pred_gain[f] < 2.f)
lpc_weighting(pred_gain[f], a[f]);
lpc_reflection(a[f], maxorder, rc[f]);
quantize_rc(rc[f], maxorder, &data->rc_order[f], data->rc[f]);
unquantize_rc(data->rc[f], data->rc_order[f], rc[f]);
}
forward_filtering(dt, bw, data->rc_order, rc, x);
}
/**
* TNS synthesis
*/
void lc3_tns_synthesize(enum lc3_dt dt, enum lc3_bandwidth bw,
const struct lc3_tns_data *data, float *x)
{
float rc[2][8] = { 0 };
for (int f = 0; f < data->nfilters; f++)
if (data->rc_order[f])
unquantize_rc(data->rc[f], data->rc_order[f], rc[f]);
inverse_filtering(dt, bw, data->rc_order, rc, x);
}
/**
* Bit consumption of bitstream data
*/
int lc3_tns_get_nbits(const struct lc3_tns_data *data)
{
int nbits = 0;
for (int f = 0; f < data->nfilters; f++) {
int nbits_2048 = 2048;
int rc_order = data->rc_order[f];
nbits_2048 += rc_order > 0 ? lc3_tns_order_bits
[data->lpc_weighting][rc_order-1] : 0;
for (int i = 0; i < rc_order; i++)
nbits_2048 += lc3_tns_coeffs_bits[i][8 + data->rc[f][i]];
nbits += (nbits_2048 + (1 << 11) - 1) >> 11;
}
return nbits;
}
/**
* Put bitstream data
*/
void lc3_tns_put_data(lc3_bits_t *bits, const struct lc3_tns_data *data)
{
for (int f = 0; f < data->nfilters; f++) {
int rc_order = data->rc_order[f];
lc3_put_bits(bits, rc_order > 0, 1);
if (rc_order <= 0)
continue;
lc3_put_symbol(bits,
lc3_tns_order_models + data->lpc_weighting, rc_order-1);
for (int i = 0; i < rc_order; i++)
lc3_put_symbol(bits,
lc3_tns_coeffs_models + i, 8 + data->rc[f][i]);
}
}
/**
* Get bitstream data
*/
int lc3_tns_get_data(lc3_bits_t *bits,
enum lc3_dt dt, enum lc3_bandwidth bw, int nbytes, lc3_tns_data_t *data)
{
data->nfilters = 1 + (dt >= LC3_DT_5M && bw >= LC3_BANDWIDTH_SWB);
data->lpc_weighting = resolve_lpc_weighting(dt, nbytes);
for (int f = 0; f < data->nfilters; f++) {
data->rc_order[f] = lc3_get_bit(bits);
if (!data->rc_order[f])
continue;
data->rc_order[f] += lc3_get_symbol(bits,
lc3_tns_order_models + data->lpc_weighting);
if (dt <= LC3_DT_5M && data->rc_order[f] > 4)
return -1;
for (int i = 0; i < data->rc_order[f]; i++)
data->rc[f][i] = (int)lc3_get_symbol(bits,
lc3_tns_coeffs_models + i) - 8;
}
return 0;
}