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-rw-r--r--Alc/filters/nfc.c426
1 files changed, 426 insertions, 0 deletions
diff --git a/Alc/filters/nfc.c b/Alc/filters/nfc.c
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+
+#include "config.h"
+
+#include "nfc.h"
+#include "alMain.h"
+
+#include <string.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.
+ */
+
+static const float B[4][3] = {
+ { 0.0f },
+ { 1.0f },
+ { 3.0f, 3.0f },
+ { 3.6778f, 6.4595f, 2.3222f },
+ /*{ 4.2076f, 11.4877f, 5.7924f, 9.1401f }*/
+};
+
+static void NfcFilterCreate1(struct NfcFilter1 *nfc, const float w0, const float w1)
+{
+ 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;
+}
+
+static void NfcFilterAdjust1(struct NfcFilter1 *nfc, const float w0)
+{
+ float b_00, g_0;
+ float r;
+
+ r = 0.5f * w0;
+ b_00 = B[1][0] * r;
+ g_0 = 1.0f + b_00;
+
+ nfc->gain = nfc->base_gain * g_0;
+ nfc->b1 = 2.0f * b_00 / g_0;
+}
+
+
+static void NfcFilterCreate2(struct NfcFilter2 *nfc, const float w0, const float w1)
+{
+ 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;
+}
+
+static void NfcFilterAdjust2(struct NfcFilter2 *nfc, const float w0)
+{
+ float b_10, b_11, g_1;
+ float r;
+
+ 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 = 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;
+}
+
+
+static void NfcFilterCreate3(struct NfcFilter3 *nfc, const float w0, const float w1)
+{
+ 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;
+ 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;
+
+ b_00 = B[3][2] * r;
+ g_0 = 1.0f + b_00;
+
+ nfc->gain *= g_0;
+ 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;
+ 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;
+
+ b_00 = B[3][2] * r;
+ g_0 = 1.0f + b_00;
+
+ nfc->base_gain /= g_0;
+ nfc->gain /= g_0;
+ nfc->a3 = 2.0f * b_00 / g_0;
+}
+
+static void NfcFilterAdjust3(struct NfcFilter3 *nfc, const float w0)
+{
+ float b_10, b_11, g_1;
+ float b_00, g_0;
+ float r;
+
+ r = 0.5f * w0;
+ b_10 = B[3][0] * r;
+ b_11 = B[3][1] * r * r;
+ 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;
+
+ b_00 = B[3][2] * r;
+ g_0 = 1.0f + b_00;
+
+ nfc->gain *= g_0;
+ nfc->b3 = 2.0f * b_00 / g_0;
+}
+
+
+void NfcFilterCreate(NfcFilter *nfc, const float w0, const float w1)
+{
+ memset(nfc, 0, sizeof(*nfc));
+ NfcFilterCreate1(&nfc->first, w0, w1);
+ NfcFilterCreate2(&nfc->second, w0, w1);
+ NfcFilterCreate3(&nfc->third, w0, w1);
+}
+
+void NfcFilterAdjust(NfcFilter *nfc, const float w0)
+{
+ NfcFilterAdjust1(&nfc->first, w0);
+ NfcFilterAdjust2(&nfc->second, w0);
+ NfcFilterAdjust3(&nfc->third, w0);
+}
+
+
+void NfcFilterProcess1(NfcFilter *nfc, float *restrict dst, const float *restrict src, const int count)
+{
+ const float gain = nfc->first.gain;
+ const float b1 = nfc->first.b1;
+ const float a1 = nfc->first.a1;
+ float z1 = nfc->first.z[0];
+ int i;
+
+ ASSUME(count > 0);
+
+ for(i = 0;i < count;i++)
+ {
+ float y = src[i]*gain - a1*z1;
+ float out = y + b1*z1;
+ z1 += y;
+
+ dst[i] = out;
+ }
+ nfc->first.z[0] = z1;
+}
+
+void NfcFilterProcess2(NfcFilter *nfc, float *restrict dst, const float *restrict src, const int count)
+{
+ const float gain = nfc->second.gain;
+ const float b1 = nfc->second.b1;
+ const float b2 = nfc->second.b2;
+ const float a1 = nfc->second.a1;
+ const float a2 = nfc->second.a2;
+ float z1 = nfc->second.z[0];
+ float z2 = nfc->second.z[1];
+ int i;
+
+ ASSUME(count > 0);
+
+ for(i = 0;i < count;i++)
+ {
+ float y = src[i]*gain - a1*z1 - a2*z2;
+ float out = y + b1*z1 + b2*z2;
+ z2 += z1;
+ z1 += y;
+
+ dst[i] = out;
+ }
+ nfc->second.z[0] = z1;
+ nfc->second.z[1] = z2;
+}
+
+void NfcFilterProcess3(NfcFilter *nfc, float *restrict dst, const float *restrict src, const int count)
+{
+ const float gain = nfc->third.gain;
+ const float b1 = nfc->third.b1;
+ const float b2 = nfc->third.b2;
+ const float b3 = nfc->third.b3;
+ const float a1 = nfc->third.a1;
+ const float a2 = nfc->third.a2;
+ const float a3 = nfc->third.a3;
+ float z1 = nfc->third.z[0];
+ float z2 = nfc->third.z[1];
+ float z3 = nfc->third.z[2];
+ int i;
+
+ ASSUME(count > 0);
+
+ for(i = 0;i < count;i++)
+ {
+ float y = src[i]*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;
+
+ dst[i] = out;
+ }
+ nfc->third.z[0] = z1;
+ nfc->third.z[1] = z2;
+ nfc->third.z[2] = z3;
+}
+
+#if 0 /* Original methods the above are derived from. */
+static void NfcFilterCreate(NfcFilter *nfc, const ALsizei order, const float src_dist, const float ctl_dist, const float rate)
+{
+ static const float B[4][5] = {
+ { },
+ { 1.0f },
+ { 3.0f, 3.0f },
+ { 3.6778f, 6.4595f, 2.3222f },
+ { 4.2076f, 11.4877f, 5.7924f, 9.1401f }
+ };
+ float w0 = SPEEDOFSOUNDMETRESPERSEC / (src_dist * rate);
+ float w1 = SPEEDOFSOUNDMETRESPERSEC / (ctl_dist * rate);
+ ALsizei i;
+ float r;
+
+ nfc->g = 1.0f;
+ nfc->coeffs[0] = 1.0f;
+
+ /* NOTE: Slight adjustment from the literature to raise the center
+ * frequency a bit (0.5 -> 1.0).
+ */
+ r = 1.0f * w0;
+ for(i = 0; i < (order-1);i += 2)
+ {
+ float b_10 = B[order][i ] * r;
+ float b_11 = B[order][i+1] * r * r;
+ float g_1 = 1.0f + b_10 + b_11;
+
+ nfc->b[i] = b_10;
+ nfc->b[i + 1] = b_11;
+ nfc->coeffs[0] *= g_1;
+ nfc->coeffs[i+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
+ nfc->coeffs[i+2] = (4.0f * b_11) / g_1;
+ }
+ if(i < order)
+ {
+ float b_00 = B[order][i] * r;
+ float g_0 = 1.0f + b_00;
+
+ nfc->b[i] = b_00;
+ nfc->coeffs[0] *= g_0;
+ nfc->coeffs[i+1] = (2.0f * b_00) / g_0;
+ }
+
+ r = 1.0f * w1;
+ for(i = 0;i < (order-1);i += 2)
+ {
+ float b_10 = B[order][i ] * r;
+ float b_11 = B[order][i+1] * r * r;
+ float g_1 = 1.0f + b_10 + b_11;
+
+ nfc->g /= g_1;
+ nfc->coeffs[0] /= g_1;
+ nfc->coeffs[order+i+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
+ nfc->coeffs[order+i+2] = (4.0f * b_11) / g_1;
+ }
+ if(i < order)
+ {
+ float b_00 = B[order][i] * r;
+ float g_0 = 1.0f + b_00;
+
+ nfc->g /= g_0;
+ nfc->coeffs[0] /= g_0;
+ nfc->coeffs[order+i+1] = (2.0f * b_00) / g_0;
+ }
+
+ for(i = 0; i < MAX_AMBI_ORDER; i++)
+ nfc->history[i] = 0.0f;
+}
+
+static void NfcFilterAdjust(NfcFilter *nfc, const float distance)
+{
+ int i;
+
+ nfc->coeffs[0] = nfc->g;
+
+ for(i = 0;i < (nfc->order-1);i += 2)
+ {
+ float b_10 = nfc->b[i] / distance;
+ float b_11 = nfc->b[i+1] / (distance * distance);
+ float g_1 = 1.0f + b_10 + b_11;
+
+ nfc->coeffs[0] *= g_1;
+ nfc->coeffs[i+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
+ nfc->coeffs[i+2] = (4.0f * b_11) / g_1;
+ }
+ if(i < nfc->order)
+ {
+ float b_00 = nfc->b[i] / distance;
+ float g_0 = 1.0f + b_00;
+
+ nfc->coeffs[0] *= g_0;
+ nfc->coeffs[i+1] = (2.0f * b_00) / g_0;
+ }
+}
+
+static float NfcFilterProcess(const float in, NfcFilter *nfc)
+{
+ int i;
+ float out = in * nfc->coeffs[0];
+
+ for(i = 0;i < (nfc->order-1);i += 2)
+ {
+ float y = out - (nfc->coeffs[nfc->order+i+1] * nfc->history[i]) -
+ (nfc->coeffs[nfc->order+i+2] * nfc->history[i+1]) + 1.0e-30f;
+ out = y + (nfc->coeffs[i+1]*nfc->history[i]) + (nfc->coeffs[i+2]*nfc->history[i+1]);
+
+ nfc->history[i+1] += nfc->history[i];
+ nfc->history[i] += y;
+ }
+ if(i < nfc->order)
+ {
+ float y = out - (nfc->coeffs[nfc->order+i+1] * nfc->history[i]) + 1.0e-30f;
+
+ out = y + (nfc->coeffs[i+1] * nfc->history[i]);
+ nfc->history[i] += y;
+ }
+
+ return out;
+}
+#endif
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