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#ifndef FILTER_NFC_H
#define FILTER_NFC_H
#include <cstddef>
#include "alspan.h"
struct NfcFilter1 {
float base_gain, gain;
float b1, a1;
float z[1];
};
struct NfcFilter2 {
float base_gain, gain;
float b1, b2, a1, a2;
float z[2];
};
struct NfcFilter3 {
float base_gain, gain;
float b1, b2, b3, a1, a2, a3;
float z[3];
};
struct NfcFilter4 {
float base_gain, gain;
float b1, b2, b3, b4, a1, a2, a3, a4;
float z[4];
};
class NfcFilter {
NfcFilter1 first;
NfcFilter2 second;
NfcFilter3 third;
NfcFilter4 fourth;
public:
/* NOTE:
* w0 = speed_of_sound / (source_distance * sample_rate);
* w1 = speed_of_sound / (control_distance * sample_rate);
*
* Generally speaking, the control distance should be approximately the
* average speaker distance, or based on the reference delay if outputing
* NFC-HOA. It must not be negative, 0, or infinite. The source distance
* should not be too small relative to the control distance.
*/
void init(const float w1) noexcept;
void adjust(const float w0) noexcept;
/* Near-field control filter for first-order ambisonic channels (1-3). */
void process1(const al::span<const float> src, float *RESTRICT dst);
/* Near-field control filter for second-order ambisonic channels (4-8). */
void process2(const al::span<const float> src, float *RESTRICT dst);
/* Near-field control filter for third-order ambisonic channels (9-15). */
void process3(const al::span<const float> src, float *RESTRICT dst);
/* Near-field control filter for fourth-order ambisonic channels (16-24). */
void process4(const al::span<const float> src, float *RESTRICT dst);
};
#endif /* FILTER_NFC_H */
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