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-rw-r--r--Alc/filters/nfc.cpp391
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diff --git a/Alc/filters/nfc.cpp b/Alc/filters/nfc.cpp
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--- a/Alc/filters/nfc.cpp
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-
-#include "config.h"
-
-#include "nfc.h"
-
-#include <algorithm>
-
-#include "alcmain.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 int 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 int 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 int 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 int 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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