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#ifndef FILTER_NFC_H
#define FILTER_NFC_H
#ifdef __cplusplus
extern "C" {
#endif
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];
};
typedef struct NfcFilter {
struct NfcFilter1 first;
struct NfcFilter2 second;
struct NfcFilter3 third;
} NfcFilter;
/* 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 NfcFilterCreate(NfcFilter *nfc, const float w0, const float w1);
void NfcFilterAdjust(NfcFilter *nfc, const float w0);
/* Near-field control filter for first-order ambisonic channels (1-3). */
void NfcFilterProcess1(NfcFilter *nfc, float *RESTRICT dst, const float *RESTRICT src, const int count);
/* Near-field control filter for second-order ambisonic channels (4-8). */
void NfcFilterProcess2(NfcFilter *nfc, float *RESTRICT dst, const float *RESTRICT src, const int count);
/* Near-field control filter for third-order ambisonic channels (9-15). */
void NfcFilterProcess3(NfcFilter *nfc, float *RESTRICT dst, const float *RESTRICT src, const int count);
#ifdef __cplusplus
} // extern "C"
#endif
#endif /* FILTER_NFC_H */
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