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/*
Copyright 2018 Google Inc. All Rights Reserved.
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 "ambisonics/ambisonic_lookup_table.h"
#include "ambisonics/ambisonic_spread_coefficients.h"
#include "ambisonics/associated_legendre_polynomials_generator.h"
#include "ambisonics/utils.h"
#include "base/constants_and_types.h"
#include "base/misc_math.h"
namespace vraudio {
namespace {
// Number of azimuth angles to store in the pre-computed encoder lookup table
// (for 0 - 90 degrees using 1 degree increments).
const size_t kNumAzimuths = 91;
// Number of elevation angles to store in the pre-computed encoder lookup table
// (for 0 - 90 degrees using 1 degree increments).
const size_t kNumElevations = 91;
// Number of Cartesian axes for which to compute spherical harmonic symmetries.
const size_t kNumAxes = 3;
// Minimum angular source spreads at different orders for which we start to
// apply spread gain correction coefficients. Array index corresponds to
// ambisonic order. For more information about sound source spread control,
// please refer to the Matlab code and the corresponding paper.
const int kMinSpreads[kMaxSupportedAmbisonicOrder + 1] = {361, 54, 40, 31};
// Spread coefficients are stored sequentially in a 1-d table. Therefore, to
// access coefficients for the required ambisonic order we need to apply offsets
// which are equal to the total number of coefficients for previous orders. For
// example, the total number of coefficient in each ambisonic order 'n' is
// equal to the number of unique orders multiplied by number of unique spreads,
// i.e.: (n + 1) * (360 - kMinSpreads[n] + 1).
const int kSpreadCoeffOffsets[kMaxSupportedAmbisonicOrder + 1] = {0, 1, 615,
1578};
size_t GetEncoderTableIndex(size_t i, size_t j, size_t k, size_t width,
size_t depth) {
return i * width * depth + j * depth + k;
}
size_t GetSymmetriesTableIndex(size_t i, size_t j, size_t width) {
return i * width + j;
}
int GetSpreadTableIndex(int ambisonic_order, float source_spread_deg) {
// Number of unique ambisonic orders in the sound field. For example, in a
// first order sound field we have components of order 0 and 1.
const int num_unique_orders = ambisonic_order + 1;
return kSpreadCoeffOffsets[ambisonic_order] +
num_unique_orders * (static_cast<int>(source_spread_deg) -
kMinSpreads[ambisonic_order]);
}
} // namespace
AmbisonicLookupTable::AmbisonicLookupTable(int max_ambisonic_order)
: max_ambisonic_order_(max_ambisonic_order),
max_num_coeffs_in_table_(
GetNumPeriphonicComponents(max_ambisonic_order_) - 1),
encoder_table_(kNumAzimuths * kNumElevations * max_num_coeffs_in_table_),
symmetries_table_(kNumAxes * max_num_coeffs_in_table_) {
DCHECK_GE(max_ambisonic_order_, 0);
DCHECK_LE(max_ambisonic_order_, kMaxSupportedAmbisonicOrder);
ComputeEncoderTable();
ComputeSymmetriesTable();
}
void AmbisonicLookupTable::GetEncodingCoeffs(
int ambisonic_order, const SphericalAngle& source_direction,
float source_spread_deg, std::vector<float>* encoding_coeffs) const {
DCHECK_GE(ambisonic_order, 0);
DCHECK_LE(ambisonic_order, kMaxSupportedAmbisonicOrder);
DCHECK_GE(source_spread_deg, 0.0f);
DCHECK_LE(source_spread_deg, 360.0f);
DCHECK(encoding_coeffs);
// Raw coefficients are stored only for ambisonic orders 1 and up, since 0th
// order raw coefficient is always 1.
const size_t num_raw_coeffs = GetNumPeriphonicComponents(ambisonic_order) - 1;
// The actual number of returned Ambisonic coefficients is therefore
// |num_raw_coeffs + 1|.
DCHECK_EQ(encoding_coeffs->size(), num_raw_coeffs + 1);
DCHECK_GE(source_direction.azimuth(), -kPi);
DCHECK_LE(source_direction.azimuth(), kTwoPi);
DCHECK_GE(source_direction.elevation(), -kHalfPi);
DCHECK_LE(source_direction.elevation(), kHalfPi);
const int azimuth_deg =
source_direction.azimuth() < kPi
? static_cast<int>(source_direction.azimuth() * kDegreesFromRadians)
: static_cast<int>(source_direction.azimuth() * kDegreesFromRadians) -
360;
const int elevation_deg =
static_cast<int>(source_direction.elevation() * kDegreesFromRadians);
const size_t abs_azimuth_deg = static_cast<size_t>(std::abs(azimuth_deg));
const size_t azimuth_idx =
abs_azimuth_deg > 90 ? 180 - abs_azimuth_deg : abs_azimuth_deg;
const size_t elevation_idx = static_cast<size_t>(std::abs(elevation_deg));
(*encoding_coeffs)[0] = 1.0f;
for (size_t raw_coeff_idx = 0; raw_coeff_idx < num_raw_coeffs;
++raw_coeff_idx) {
// Variable to hold information about spherical harmonic phase flip. 1 means
// no flip; -1 means 180 degrees flip.
float flip = 1.0f;
// The following three 'if' statements implement the logic to correct the
// phase of the current spherical harmonic, depending on which quadrant the
// sound source is located in. For more information, please see the Matlab
// code and the corresponding paper.
if (azimuth_deg < 0) {
flip = symmetries_table_[GetSymmetriesTableIndex(
0, raw_coeff_idx, max_num_coeffs_in_table_)];
}
if (elevation_deg < 0) {
flip *= symmetries_table_[GetSymmetriesTableIndex(
1, raw_coeff_idx, max_num_coeffs_in_table_)];
}
if (abs_azimuth_deg > 90) {
flip *= symmetries_table_[GetSymmetriesTableIndex(
2, raw_coeff_idx, max_num_coeffs_in_table_)];
}
const size_t encoder_table_idx =
GetEncoderTableIndex(azimuth_idx, elevation_idx, raw_coeff_idx,
kNumElevations, max_num_coeffs_in_table_);
(*encoding_coeffs)[raw_coeff_idx + 1] =
encoder_table_[encoder_table_idx] * flip;
}
// If the spread is more than min. theoretical spread for the given
// |ambisonic_order|, multiply the encoding coefficients by the required
// spread control gains from the |kSpreadCoeffs| lookup table.
if (source_spread_deg >= kMinSpreads[ambisonic_order]) {
const int spread_table_idx =
GetSpreadTableIndex(ambisonic_order, source_spread_deg);
(*encoding_coeffs)[0] *= kSpreadCoeffs[spread_table_idx];
for (size_t coeff = 1; coeff < encoding_coeffs->size(); ++coeff) {
const int current_coefficient_degree =
GetPeriphonicAmbisonicOrderForChannel(coeff);
(*encoding_coeffs)[coeff] *=
kSpreadCoeffs[spread_table_idx + current_coefficient_degree];
}
}
}
void AmbisonicLookupTable::ComputeEncoderTable() {
// Associated Legendre polynomial generator.
AssociatedLegendrePolynomialsGenerator alp_generator(
max_ambisonic_order_, /*condon_shortley_phase=*/false,
/*compute_negative_order=*/false);
// Temporary storage for associated Legendre polynomials generated.
std::vector<float> temp_associated_legendre_polynomials;
for (size_t azimuth_idx = 0; azimuth_idx < kNumAzimuths; ++azimuth_idx) {
for (size_t elevation_idx = 0; elevation_idx < kNumElevations;
++elevation_idx) {
const SphericalAngle angle(
static_cast<float>(azimuth_idx) * kRadiansFromDegrees,
static_cast<float>(elevation_idx) * kRadiansFromDegrees);
temp_associated_legendre_polynomials =
alp_generator.Generate(std::sin(angle.elevation()));
// First spherical harmonic is always equal 1 for all angles so we do not
// need to compute and store it.
for (int degree = 1; degree <= max_ambisonic_order_; ++degree) {
for (int order = -degree; order <= degree; ++order) {
const size_t alp_index =
alp_generator.GetIndex(degree, std::abs(order));
const float alp_value =
temp_associated_legendre_polynomials[alp_index];
const size_t raw_coeff_idx = AcnSequence(degree, order) - 1;
const size_t encoder_table_idx =
GetEncoderTableIndex(azimuth_idx, elevation_idx, raw_coeff_idx,
kNumElevations, max_num_coeffs_in_table_);
encoder_table_[encoder_table_idx] =
Sn3dNormalization(degree, order) *
UnnormalizedSphericalHarmonic(alp_value, order, angle.azimuth());
}
}
}
}
}
void AmbisonicLookupTable::ComputeSymmetriesTable() {
for (int degree = 1; degree <= max_ambisonic_order_; ++degree) {
for (int order = -degree; order <= degree; ++order) {
const size_t raw_coeff_idx = AcnSequence(degree, order) - 1;
// Symmetry wrt the left-right axis (Y).
symmetries_table_[GetSymmetriesTableIndex(0, raw_coeff_idx,
max_num_coeffs_in_table_)] =
order < 0 ? -1.0f : 1.0f;
// Symmetry wrt the up-down axis (Z).
symmetries_table_[GetSymmetriesTableIndex(1, raw_coeff_idx,
max_num_coeffs_in_table_)] =
static_cast<float>(IntegerPow(-1, degree + order));
// Symmetry wrt the front-back axis (X).
symmetries_table_[GetSymmetriesTableIndex(2, raw_coeff_idx,
max_num_coeffs_in_table_)] =
order < 0 ? static_cast<float>(-IntegerPow(-1, std::abs(order)))
: static_cast<float>(IntegerPow(-1, order));
}
}
}
float AmbisonicLookupTable::UnnormalizedSphericalHarmonic(float alp_value,
int order,
float azimuth_rad) {
const float horizontal_term =
(order >= 0) ? std::cos(static_cast<float>(order) * azimuth_rad)
: std::sin(static_cast<float>(-order) * azimuth_rad);
return alp_value * horizontal_term;
}
} // namespace vraudio
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