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#include "config.h"
#include "nfcfilter.h"
#include "alu.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 }*/
};
void NfcFilterCreate1(NfcFilter *nfc, const float w0, const float w1)
{
float b_00, g_0;
float r;
memset(nfc, 0, sizeof(*nfc));
nfc->g = 1.0f;
nfc->coeffs[0] = 1.0f;
/* Calculate bass-boost coefficients. */
r = 0.5f * w0;
b_00 = B[1][0] * r;
g_0 = 1.0f + b_00;
nfc->coeffs[0] *= g_0;
nfc->coeffs[1] = (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->g /= g_0;
nfc->coeffs[0] /= g_0;
nfc->coeffs[1+1] = (2.0f * b_00) / g_0;
}
void NfcFilterAdjust1(NfcFilter *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->coeffs[0] = nfc->g * g_0;
nfc->coeffs[1] = (2.0f * b_00) / g_0;
}
void NfcFilterUpdate1(NfcFilter *nfc, ALfloat *restrict dst, const float *restrict src, const int count)
{
const float b0 = nfc->coeffs[0];
const float a0 = nfc->coeffs[1];
const float a1 = nfc->coeffs[2];
float z1 = nfc->history[0];
int i;
for(i = 0;i < count;i++)
{
float out = src[i] * b0;
float y;
y = out - (a1*z1);
out = y + (a0*z1);
z1 += y;
dst[i] = out;
}
nfc->history[0] = z1;
}
void NfcFilterCreate2(NfcFilter *nfc, const float w0, const float w1)
{
float b_10, b_11, g_1;
float r;
memset(nfc, 0, sizeof(*nfc));
nfc->g = 1.0f;
nfc->coeffs[0] = 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->coeffs[0] *= g_1;
nfc->coeffs[1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
nfc->coeffs[2] = (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->g /= g_1;
nfc->coeffs[0] /= g_1;
nfc->coeffs[2+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
nfc->coeffs[2+2] = (4.0f * b_11) / g_1;
}
void NfcFilterAdjust2(NfcFilter *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->coeffs[0] = nfc->g * g_1;
nfc->coeffs[1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
nfc->coeffs[2] = (4.0f * b_11) / g_1;
}
void NfcFilterUpdate2(NfcFilter *nfc, ALfloat *restrict dst, const float *restrict src, const int count)
{
const float b0 = nfc->coeffs[0];
const float a00 = nfc->coeffs[1];
const float a01 = nfc->coeffs[2];
const float a10 = nfc->coeffs[3];
const float a11 = nfc->coeffs[4];
float z1 = nfc->history[0];
float z2 = nfc->history[1];
int i;
for(i = 0;i < count;i++)
{
float out = src[i] * b0;
float y;
y = out - (a10*z1) - (a11*z2);
out = y + (a00*z1) + (a01*z2);
z2 += z1;
z1 += y;
dst[i] = out;
}
nfc->history[0] = z1;
nfc->history[1] = z2;
}
void NfcFilterCreate3(NfcFilter *nfc, const float w0, const float w1)
{
float b_10, b_11, g_1;
float b_00, g_0;
float r;
memset(nfc, 0, sizeof(*nfc));
nfc->g = 1.0f;
nfc->coeffs[0] = 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->coeffs[0] *= g_1;
nfc->coeffs[1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
nfc->coeffs[2] = (4.0f * b_11) / g_1;
b_00 = B[3][2] * r;
g_0 = 1.0f + b_00;
nfc->coeffs[0] *= g_0;
nfc->coeffs[2+1] = (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->g /= g_1;
nfc->coeffs[0] /= g_1;
nfc->coeffs[3+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
nfc->coeffs[3+2] = (4.0f * b_11) / g_1;
b_00 = B[3][2] * r;
g_0 = 1.0f + b_00;
nfc->g /= g_0;
nfc->coeffs[0] /= g_0;
nfc->coeffs[3+2+1] = (2.0f * b_00) / g_0;
}
void NfcFilterAdjust3(NfcFilter *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->coeffs[0] = nfc->g * g_1;
nfc->coeffs[1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
nfc->coeffs[2] = (4.0f * b_11) / g_1;
b_00 = B[3][2] * r;
g_0 = 1.0f + b_00;
nfc->coeffs[0] *= g_0;
nfc->coeffs[2+1] = (2.0f * b_00) / g_0;
}
void NfcFilterUpdate3(NfcFilter *nfc, ALfloat *restrict dst, const float *restrict src, const int count)
{
const float b0 = nfc->coeffs[0];
const float a00 = nfc->coeffs[1];
const float a01 = nfc->coeffs[2];
const float a02 = nfc->coeffs[3];
const float a10 = nfc->coeffs[4];
const float a11 = nfc->coeffs[5];
const float a12 = nfc->coeffs[6];
float z1 = nfc->history[0];
float z2 = nfc->history[1];
float z3 = nfc->history[2];
int i;
for(i = 0;i < count;i++)
{
float out = src[i] * b0;
float y;
y = out - (a10*z1) - (a11*z2);
out = y + (a00*z1) + (a01*z2);
z2 += z1;
z1 += y;
y = out - (a12*z3);
out = y + (a02*z3);
z3 += y;
dst[i] = out;
}
nfc->history[0] = z1;
nfc->history[1] = z2;
nfc->history[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 NfcFilterUpdate(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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