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openal-soft/alc/filters/nfc.cpp

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#include "config.h"
#include "nfc.h"
#include <algorithm>
#include "opthelpers.h"
/* Near-field control filters are the basis for handling the near-field effect.
* The near-field effect is a bass-boost present in the directional components
* of a recorded signal, created as a result of the wavefront curvature (itself
* a function of sound distance). Proper reproduction dictates this be
* compensated for using a bass-cut given the playback speaker distance, to
* avoid excessive bass in the playback.
*
* For real-time rendered audio, emulating the near-field effect based on the
* sound source's distance, and subsequently compensating for it at output
* based on the speaker distances, can create a more realistic perception of
* sound distance beyond a simple 1/r attenuation.
*
* These filters do just that. Each one applies a low-shelf filter, created as
* the combination of a bass-boost for a given sound source distance (near-
* field emulation) along with a bass-cut for a given control/speaker distance
* (near-field compensation).
*
* Note that it is necessary to apply a cut along with the boost, since the
* boost alone is unstable in higher-order ambisonics as it causes an infinite
* DC gain (even first-order ambisonics requires there to be no DC offset for
* the boost to work). Consequently, ambisonics requires a control parameter to
* be used to avoid an unstable boost-only filter. NFC-HOA defines this control
* as a reference delay, calculated with:
*
* reference_delay = control_distance / speed_of_sound
*
* This means w0 (for input) or w1 (for output) should be set to:
*
* wN = 1 / (reference_delay * sample_rate)
*
* when dealing with NFC-HOA content. For FOA input content, which does not
* specify a reference_delay variable, w0 should be set to 0 to apply only
* near-field compensation for output. It's important that w1 be a finite,
* positive, non-0 value or else the bass-boost will become unstable again.
* Also, w0 should not be too large compared to w1, to avoid excessively loud
* low frequencies.
*/
namespace {
constexpr float B[5][4] = {
{ 0.0f },
{ 1.0f },
{ 3.0f, 3.0f },
{ 3.6778f, 6.4595f, 2.3222f },
{ 4.2076f, 11.4877f, 5.7924f, 9.1401f }
};
NfcFilter1 NfcFilterCreate1(const float w0, const float w1) noexcept
{
NfcFilter1 nfc{};
float b_00, g_0;
float r;
nfc.base_gain = 1.0f;
nfc.gain = 1.0f;
/* Calculate bass-boost coefficients. */
r = 0.5f * w0;
b_00 = B[1][0] * r;
g_0 = 1.0f + b_00;
nfc.gain *= g_0;
nfc.b1 = 2.0f * b_00 / g_0;
/* Calculate bass-cut coefficients. */
r = 0.5f * w1;
b_00 = B[1][0] * r;
g_0 = 1.0f + b_00;
nfc.base_gain /= g_0;
nfc.gain /= g_0;
nfc.a1 = 2.0f * b_00 / g_0;
return nfc;
}
void NfcFilterAdjust1(NfcFilter1 *nfc, const float w0) noexcept
{
const float r{0.5f * w0};
const float b_00{B[1][0] * r};
const float g_0{1.0f + b_00};
nfc->gain = nfc->base_gain * g_0;
nfc->b1 = 2.0f * b_00 / g_0;
}
NfcFilter2 NfcFilterCreate2(const float w0, const float w1) noexcept
{
NfcFilter2 nfc{};
float b_10, b_11, g_1;
float r;
nfc.base_gain = 1.0f;
nfc.gain = 1.0f;
/* Calculate bass-boost coefficients. */
r = 0.5f * w0;
b_10 = B[2][0] * r;
b_11 = B[2][1] * r * r;
g_1 = 1.0f + b_10 + b_11;
nfc.gain *= g_1;
nfc.b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc.b2 = 4.0f * b_11 / g_1;
/* Calculate bass-cut coefficients. */
r = 0.5f * w1;
b_10 = B[2][0] * r;
b_11 = B[2][1] * r * r;
g_1 = 1.0f + b_10 + b_11;
nfc.base_gain /= g_1;
nfc.gain /= g_1;
nfc.a1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc.a2 = 4.0f * b_11 / g_1;
return nfc;
}
void NfcFilterAdjust2(NfcFilter2 *nfc, const float w0) noexcept
{
const float r{0.5f * w0};
const float b_10{B[2][0] * r};
const float b_11{B[2][1] * r * r};
const float g_1{1.0f + b_10 + b_11};
nfc->gain = nfc->base_gain * g_1;
nfc->b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc->b2 = 4.0f * b_11 / g_1;
}
NfcFilter3 NfcFilterCreate3(const float w0, const float w1) noexcept
{
NfcFilter3 nfc{};
float b_10, b_11, g_1;
float b_00, g_0;
float r;
nfc.base_gain = 1.0f;
nfc.gain = 1.0f;
/* Calculate bass-boost coefficients. */
r = 0.5f * w0;
b_10 = B[3][0] * r;
b_11 = B[3][1] * r * r;
b_00 = B[3][2] * r;
g_1 = 1.0f + b_10 + b_11;
g_0 = 1.0f + b_00;
nfc.gain *= g_1 * g_0;
nfc.b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc.b2 = 4.0f * b_11 / g_1;
nfc.b3 = 2.0f * b_00 / g_0;
/* Calculate bass-cut coefficients. */
r = 0.5f * w1;
b_10 = B[3][0] * r;
b_11 = B[3][1] * r * r;
b_00 = B[3][2] * r;
g_1 = 1.0f + b_10 + b_11;
g_0 = 1.0f + b_00;
nfc.base_gain /= g_1 * g_0;
nfc.gain /= g_1 * g_0;
nfc.a1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc.a2 = 4.0f * b_11 / g_1;
nfc.a3 = 2.0f * b_00 / g_0;
return nfc;
}
void NfcFilterAdjust3(NfcFilter3 *nfc, const float w0) noexcept
{
const float r{0.5f * w0};
const float b_10{B[3][0] * r};
const float b_11{B[3][1] * r * r};
const float b_00{B[3][2] * r};
const float g_1{1.0f + b_10 + b_11};
const float g_0{1.0f + b_00};
nfc->gain = nfc->base_gain * g_1 * g_0;
nfc->b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc->b2 = 4.0f * b_11 / g_1;
nfc->b3 = 2.0f * b_00 / g_0;
}
NfcFilter4 NfcFilterCreate4(const float w0, const float w1) noexcept
{
NfcFilter4 nfc{};
float b_10, b_11, g_1;
float b_00, b_01, g_0;
float r;
nfc.base_gain = 1.0f;
nfc.gain = 1.0f;
/* Calculate bass-boost coefficients. */
r = 0.5f * w0;
b_10 = B[4][0] * r;
b_11 = B[4][1] * r * r;
b_00 = B[4][2] * r;
b_01 = B[4][3] * r * r;
g_1 = 1.0f + b_10 + b_11;
g_0 = 1.0f + b_00 + b_01;
nfc.gain *= g_1 * g_0;
nfc.b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc.b2 = 4.0f * b_11 / g_1;
nfc.b3 = (2.0f*b_00 + 4.0f*b_01) / g_0;
nfc.b4 = 4.0f * b_01 / g_0;
/* Calculate bass-cut coefficients. */
r = 0.5f * w1;
b_10 = B[4][0] * r;
b_11 = B[4][1] * r * r;
b_00 = B[4][2] * r;
b_01 = B[4][3] * r * r;
g_1 = 1.0f + b_10 + b_11;
g_0 = 1.0f + b_00 + b_01;
nfc.base_gain /= g_1 * g_0;
nfc.gain /= g_1 * g_0;
nfc.a1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc.a2 = 4.0f * b_11 / g_1;
nfc.a3 = (2.0f*b_00 + 4.0f*b_01) / g_0;
nfc.a4 = 4.0f * b_01 / g_0;
return nfc;
}
void NfcFilterAdjust4(NfcFilter4 *nfc, const float w0) noexcept
{
const float r{0.5f * w0};
const float b_10{B[4][0] * r};
const float b_11{B[4][1] * r * r};
const float b_00{B[4][2] * r};
const float b_01{B[4][3] * r * r};
const float g_1{1.0f + b_10 + b_11};
const float g_0{1.0f + b_00 + b_01};
nfc->gain = nfc->base_gain * g_1 * g_0;
nfc->b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
nfc->b2 = 4.0f * b_11 / g_1;
nfc->b3 = (2.0f*b_00 + 4.0f*b_01) / g_0;
nfc->b4 = 4.0f * b_01 / g_0;
}
} // namespace
void NfcFilter::init(const float w1) noexcept
{
first = NfcFilterCreate1(0.0f, w1);
second = NfcFilterCreate2(0.0f, w1);
third = NfcFilterCreate3(0.0f, w1);
fourth = NfcFilterCreate4(0.0f, w1);
}
void NfcFilter::adjust(const float w0) noexcept
{
NfcFilterAdjust1(&first, w0);
NfcFilterAdjust2(&second, w0);
NfcFilterAdjust3(&third, w0);
NfcFilterAdjust4(&fourth, w0);
}
void NfcFilter::process1(float *RESTRICT dst, const float *RESTRICT src, const size_t count)
{
ASSUME(count > 0);
const float gain{first.gain};
const float b1{first.b1};
const float a1{first.a1};
float z1{first.z[0]};
auto proc_sample = [gain,b1,a1,&z1](const float in) noexcept -> float
{
const float y{in*gain - a1*z1};
const float out{y + b1*z1};
z1 += y;
return out;
};
std::transform(src, src+count, dst, proc_sample);
first.z[0] = z1;
}
void NfcFilter::process2(float *RESTRICT dst, const float *RESTRICT src, const size_t count)
{
ASSUME(count > 0);
const float gain{second.gain};
const float b1{second.b1};
const float b2{second.b2};
const float a1{second.a1};
const float a2{second.a2};
float z1{second.z[0]};
float z2{second.z[1]};
auto proc_sample = [gain,b1,b2,a1,a2,&z1,&z2](const float in) noexcept -> float
{
const float y{in*gain - a1*z1 - a2*z2};
const float out{y + b1*z1 + b2*z2};
z2 += z1;
z1 += y;
return out;
};
std::transform(src, src+count, dst, proc_sample);
second.z[0] = z1;
second.z[1] = z2;
}
void NfcFilter::process3(float *RESTRICT dst, const float *RESTRICT src, const size_t count)
{
ASSUME(count > 0);
const float gain{third.gain};
const float b1{third.b1};
const float b2{third.b2};
const float b3{third.b3};
const float a1{third.a1};
const float a2{third.a2};
const float a3{third.a3};
float z1{third.z[0]};
float z2{third.z[1]};
float z3{third.z[2]};
auto proc_sample = [gain,b1,b2,b3,a1,a2,a3,&z1,&z2,&z3](const float in) noexcept -> float
{
float y{in*gain - a1*z1 - a2*z2};
float out{y + b1*z1 + b2*z2};
z2 += z1;
z1 += y;
y = out - a3*z3;
out = y + b3*z3;
z3 += y;
return out;
};
std::transform(src, src+count, dst, proc_sample);
third.z[0] = z1;
third.z[1] = z2;
third.z[2] = z3;
}
void NfcFilter::process4(float *RESTRICT dst, const float *RESTRICT src, const size_t count)
{
ASSUME(count > 0);
const float gain{fourth.gain};
const float b1{fourth.b1};
const float b2{fourth.b2};
const float b3{fourth.b3};
const float b4{fourth.b4};
const float a1{fourth.a1};
const float a2{fourth.a2};
const float a3{fourth.a3};
const float a4{fourth.a4};
float z1{fourth.z[0]};
float z2{fourth.z[1]};
float z3{fourth.z[2]};
float z4{fourth.z[3]};
auto proc_sample = [gain,b1,b2,b3,b4,a1,a2,a3,a4,&z1,&z2,&z3,&z4](const float in) noexcept -> float
{
float y{in*gain - a1*z1 - a2*z2};
float out{y + b1*z1 + b2*z2};
z2 += z1;
z1 += y;
y = out - a3*z3 - a4*z4;
out = y + b3*z3 + b4*z4;
z4 += z3;
z3 += y;
return out;
};
std::transform(src, src+count, dst, proc_sample);
fourth.z[0] = z1;
fourth.z[1] = z2;
fourth.z[2] = z3;
fourth.z[3] = z4;
}
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