Add fourth-order methods to the NFC filter
Unused, but it finishes out the currently possible implementations.
This commit is contained in:
Chris Robinson
+112
-120
@@ -50,12 +50,12 @@
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namespace {
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constexpr float B[4][3] = {
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constexpr float B[5][4] = {
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{ 0.0f },
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{ 1.0f },
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{ 3.0f, 3.0f },
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{ 3.6778f, 6.4595f, 2.3222f },
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/*{ 4.2076f, 11.4877f, 5.7924f, 9.1401f }*/
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{ 4.2076f, 11.4877f, 5.7924f, 9.1401f }
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};
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NfcFilter1 NfcFilterCreate1(const float w0, const float w1) noexcept
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@@ -219,6 +219,81 @@ void NfcFilterAdjust3(NfcFilter3 *nfc, const float w0) noexcept
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nfc->b3 = 2.0f * b_00 / g_0;
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}
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NfcFilter4 NfcFilterCreate4(const float w0, const float w1) noexcept
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{
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NfcFilter4 nfc{};
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float b_10, b_11, g_1;
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float r;
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nfc.base_gain = 1.0f;
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nfc.gain = 1.0f;
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/* Calculate bass-boost coefficients. */
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r = 0.5f * w0;
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b_10 = B[4][0] * r;
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b_11 = B[4][1] * r * r;
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g_1 = 1.0f + b_10 + b_11;
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nfc.gain *= g_1;
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nfc.b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
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nfc.b2 = 4.0f * b_11 / g_1;
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b_10 = B[4][2] * r;
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b_11 = B[4][3] * r * r;
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g_1 = 1.0f + b_10 + b_11;
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nfc.gain *= g_1;
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nfc.b3 = (2.0f*b_10 + 4.0f*b_11) / g_1;
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nfc.b4 = 4.0f * b_11 / g_1;
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/* Calculate bass-cut coefficients. */
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r = 0.5f * w1;
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b_10 = B[4][0] * r;
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b_11 = B[4][1] * r * r;
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g_1 = 1.0f + b_10 + b_11;
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nfc.base_gain /= g_1;
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nfc.gain /= g_1;
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nfc.a1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
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nfc.a2 = 4.0f * b_11 / g_1;
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b_10 = B[4][2] * r;
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b_11 = B[4][3] * r * r;
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g_1 = 1.0f + b_10 + b_11;
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nfc.base_gain /= g_1;
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nfc.gain /= g_1;
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nfc.a3 = (2.0f*b_10 + 4.0f*b_11) / g_1;
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nfc.a4 = 4.0f * b_11 / g_1;
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return nfc;
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}
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void NfcFilterAdjust4(NfcFilter4 *nfc, const float w0) noexcept
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{
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float b_10, b_11, g_1;
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float r;
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r = 0.5f * w0;
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b_10 = B[4][0] * r;
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b_11 = B[4][1] * r * r;
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g_1 = 1.0f + b_10 + b_11;
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nfc->gain = nfc->base_gain * g_1;
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nfc->b1 = (2.0f*b_10 + 4.0f*b_11) / g_1;
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nfc->b2 = 4.0f * b_11 / g_1;
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b_10 = B[4][2] * r;
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b_11 = B[4][3] * r * r;
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g_1 = 1.0f + b_10 + b_11;
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nfc->gain *= nfc->base_gain * g_1;
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nfc->b3 = (2.0f*b_10 + 4.0f*b_11) / g_1;
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nfc->b4 = 4.0f * b_11 / g_1;
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}
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} // namespace
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void NfcFilter::init(const float w0, const float w1) noexcept
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@@ -226,6 +301,7 @@ void NfcFilter::init(const float w0, const float w1) noexcept
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first = NfcFilterCreate1(w0, w1);
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second = NfcFilterCreate2(w0, w1);
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third = NfcFilterCreate3(w0, w1);
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fourth = NfcFilterCreate4(w0, w1);
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}
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void NfcFilter::adjust(const float w0) noexcept
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@@ -233,6 +309,7 @@ void NfcFilter::adjust(const float w0) noexcept
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NfcFilterAdjust1(&first, w0);
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NfcFilterAdjust2(&second, w0);
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NfcFilterAdjust3(&third, w0);
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NfcFilterAdjust4(&fourth, w0);
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}
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@@ -311,124 +388,39 @@ void NfcFilter::process3(float *RESTRICT dst, const float *RESTRICT src, const i
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third.z[2] = z3;
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}
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#if 0 /* Original methods the above are derived from. */
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static void NfcFilterCreate(NfcFilter *nfc, const ALsizei order, const float src_dist, const float ctl_dist, const float rate)
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void NfcFilter::process4(float *RESTRICT dst, const float *RESTRICT src, const int count)
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{
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static const float B[4][5] = {
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{ },
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{ 1.0f },
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{ 3.0f, 3.0f },
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{ 3.6778f, 6.4595f, 2.3222f },
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{ 4.2076f, 11.4877f, 5.7924f, 9.1401f }
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ASSUME(count > 0);
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const float gain{fourth.gain};
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const float b1{fourth.b1};
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const float b2{fourth.b2};
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const float b3{fourth.b3};
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const float b4{fourth.b4};
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const float a1{fourth.a1};
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const float a2{fourth.a2};
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const float a3{fourth.a3};
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const float a4{fourth.a4};
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float z1{fourth.z[0]};
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float z2{fourth.z[1]};
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float z3{fourth.z[2]};
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float z4{fourth.z[3]};
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auto proc_sample = [gain,b1,b2,b3,b4,a1,a2,a3,a4,&z1,&z2,&z3,&z4](const float in) noexcept -> float
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{
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float y{in*gain - a1*z1 - a2*z2};
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float out{y + b1*z1 + b2*z2};
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z2 += z1;
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z1 += y;
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y = out - a3*z3 - a4*z4;
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out = y + b3*z3 + b4*z4;
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z4 += z3;
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z3 += y;
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return out;
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};
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float w0 = SPEEDOFSOUNDMETRESPERSEC / (src_dist * rate);
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float w1 = SPEEDOFSOUNDMETRESPERSEC / (ctl_dist * rate);
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ALsizei i;
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float r;
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nfc->g = 1.0f;
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nfc->coeffs[0] = 1.0f;
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/* NOTE: Slight adjustment from the literature to raise the center
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* frequency a bit (0.5 -> 1.0).
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*/
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r = 1.0f * w0;
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for(i = 0; i < (order-1);i += 2)
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{
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float b_10 = B[order][i ] * r;
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float b_11 = B[order][i+1] * r * r;
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float g_1 = 1.0f + b_10 + b_11;
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nfc->b[i] = b_10;
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nfc->b[i + 1] = b_11;
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nfc->coeffs[0] *= g_1;
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nfc->coeffs[i+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
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nfc->coeffs[i+2] = (4.0f * b_11) / g_1;
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}
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if(i < order)
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{
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float b_00 = B[order][i] * r;
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float g_0 = 1.0f + b_00;
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nfc->b[i] = b_00;
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nfc->coeffs[0] *= g_0;
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nfc->coeffs[i+1] = (2.0f * b_00) / g_0;
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}
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r = 1.0f * w1;
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for(i = 0;i < (order-1);i += 2)
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{
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float b_10 = B[order][i ] * r;
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float b_11 = B[order][i+1] * r * r;
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float g_1 = 1.0f + b_10 + b_11;
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nfc->g /= g_1;
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nfc->coeffs[0] /= g_1;
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nfc->coeffs[order+i+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
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nfc->coeffs[order+i+2] = (4.0f * b_11) / g_1;
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}
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if(i < order)
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{
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float b_00 = B[order][i] * r;
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float g_0 = 1.0f + b_00;
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nfc->g /= g_0;
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nfc->coeffs[0] /= g_0;
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nfc->coeffs[order+i+1] = (2.0f * b_00) / g_0;
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}
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for(i = 0; i < MAX_AMBI_ORDER; i++)
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nfc->history[i] = 0.0f;
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std::transform(src, src+count, dst, proc_sample);
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fourth.z[0] = z1;
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fourth.z[1] = z2;
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fourth.z[2] = z3;
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fourth.z[3] = z4;
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}
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static void NfcFilterAdjust(NfcFilter *nfc, const float distance)
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{
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int i;
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nfc->coeffs[0] = nfc->g;
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for(i = 0;i < (nfc->order-1);i += 2)
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{
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float b_10 = nfc->b[i] / distance;
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float b_11 = nfc->b[i+1] / (distance * distance);
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float g_1 = 1.0f + b_10 + b_11;
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nfc->coeffs[0] *= g_1;
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nfc->coeffs[i+1] = ((2.0f * b_10) + (4.0f * b_11)) / g_1;
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nfc->coeffs[i+2] = (4.0f * b_11) / g_1;
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}
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if(i < nfc->order)
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{
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float b_00 = nfc->b[i] / distance;
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float g_0 = 1.0f + b_00;
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nfc->coeffs[0] *= g_0;
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nfc->coeffs[i+1] = (2.0f * b_00) / g_0;
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}
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}
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static float NfcFilterProcess(const float in, NfcFilter *nfc)
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{
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int i;
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float out = in * nfc->coeffs[0];
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for(i = 0;i < (nfc->order-1);i += 2)
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{
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float y = out - (nfc->coeffs[nfc->order+i+1] * nfc->history[i]) -
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(nfc->coeffs[nfc->order+i+2] * nfc->history[i+1]) + 1.0e-30f;
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out = y + (nfc->coeffs[i+1]*nfc->history[i]) + (nfc->coeffs[i+2]*nfc->history[i+1]);
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nfc->history[i+1] += nfc->history[i];
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nfc->history[i] += y;
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}
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if(i < nfc->order)
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{
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float y = out - (nfc->coeffs[nfc->order+i+1] * nfc->history[i]) + 1.0e-30f;
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out = y + (nfc->coeffs[i+1] * nfc->history[i]);
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nfc->history[i] += y;
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}
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return out;
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}
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#endif
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@@ -16,11 +16,17 @@ struct NfcFilter3 {
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float b1, b2, b3, a1, a2, a3;
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float z[3];
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};
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struct NfcFilter4 {
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float base_gain, gain;
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float b1, b2, b3, b4, a1, a2, a3, a4;
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float z[4];
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};
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class NfcFilter {
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NfcFilter1 first;
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NfcFilter2 second;
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NfcFilter3 third;
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NfcFilter4 fourth;
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public:
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/* NOTE:
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@@ -44,6 +50,9 @@ public:
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/* Near-field control filter for third-order ambisonic channels (9-15). */
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void process3(float *RESTRICT dst, const float *RESTRICT src, const int count);
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/* Near-field control filter for fourth-order ambisonic channels (16-24). */
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void process4(float *RESTRICT dst, const float *RESTRICT src, const int count);
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};
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#endif /* FILTER_NFC_H */
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