95 lines
3.0 KiB
C++
95 lines
3.0 KiB
C++
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#include "config.h"
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#include "mixer.h"
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#include <cmath>
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#include "alnumbers.h"
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#include "devformat.h"
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#include "device.h"
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#include "mixer/defs.h"
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struct CTag;
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MixerFunc MixSamples{Mix_<CTag>};
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std::array<float,MaxAmbiChannels> CalcAmbiCoeffs(const float y, const float z, const float x,
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const float spread)
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{
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std::array<float,MaxAmbiChannels> coeffs{CalcAmbiCoeffs(y, z, x)};
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if(spread > 0.0f)
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{
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/* Implement the spread by using a spherical source that subtends the
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* angle spread. See:
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* http://www.ppsloan.org/publications/StupidSH36.pdf - Appendix A3
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*
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* When adjusted for N3D normalization instead of SN3D, these
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* calculations are:
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*
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* ZH0 = -sqrt(pi) * (-1+ca);
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* ZH1 = 0.5*sqrt(pi) * sa*sa;
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* ZH2 = -0.5*sqrt(pi) * ca*(-1+ca)*(ca+1);
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* ZH3 = -0.125*sqrt(pi) * (-1+ca)*(ca+1)*(5*ca*ca - 1);
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* ZH4 = -0.125*sqrt(pi) * ca*(-1+ca)*(ca+1)*(7*ca*ca - 3);
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* ZH5 = -0.0625*sqrt(pi) * (-1+ca)*(ca+1)*(21*ca*ca*ca*ca - 14*ca*ca + 1);
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*
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* The gain of the source is compensated for size, so that the
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* loudness doesn't depend on the spread. Thus:
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*
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* ZH0 = 1.0f;
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* ZH1 = 0.5f * (ca+1.0f);
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* ZH2 = 0.5f * (ca+1.0f)*ca;
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* ZH3 = 0.125f * (ca+1.0f)*(5.0f*ca*ca - 1.0f);
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* ZH4 = 0.125f * (ca+1.0f)*(7.0f*ca*ca - 3.0f)*ca;
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* ZH5 = 0.0625f * (ca+1.0f)*(21.0f*ca*ca*ca*ca - 14.0f*ca*ca + 1.0f);
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*/
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const float ca{std::cos(spread * 0.5f)};
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/* Increase the source volume by up to +3dB for a full spread. */
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const float scale{std::sqrt(1.0f + al::numbers::inv_pi_v<float>/2.0f*spread)};
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const float ZH0_norm{scale};
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const float ZH1_norm{scale * 0.5f * (ca+1.f)};
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const float ZH2_norm{scale * 0.5f * (ca+1.f)*ca};
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const float ZH3_norm{scale * 0.125f * (ca+1.f)*(5.f*ca*ca-1.f)};
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/* Zeroth-order */
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coeffs[0] *= ZH0_norm;
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/* First-order */
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coeffs[1] *= ZH1_norm;
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coeffs[2] *= ZH1_norm;
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coeffs[3] *= ZH1_norm;
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/* Second-order */
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coeffs[4] *= ZH2_norm;
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coeffs[5] *= ZH2_norm;
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coeffs[6] *= ZH2_norm;
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coeffs[7] *= ZH2_norm;
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coeffs[8] *= ZH2_norm;
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/* Third-order */
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coeffs[9] *= ZH3_norm;
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coeffs[10] *= ZH3_norm;
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coeffs[11] *= ZH3_norm;
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coeffs[12] *= ZH3_norm;
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coeffs[13] *= ZH3_norm;
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coeffs[14] *= ZH3_norm;
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coeffs[15] *= ZH3_norm;
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}
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return coeffs;
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}
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void ComputePanGains(const MixParams *mix, const float*RESTRICT coeffs, const float ingain,
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const al::span<float,MaxAmbiChannels> gains)
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{
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auto ambimap = mix->AmbiMap.cbegin();
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auto iter = std::transform(ambimap, ambimap+mix->Buffer.size(), gains.begin(),
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[coeffs,ingain](const BFChannelConfig &chanmap) noexcept -> float
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{ return chanmap.Scale * coeffs[chanmap.Index] * ingain; }
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);
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std::fill(iter, gains.end(), 0.0f);
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}
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