Alc/filters/nfc.h

   1 #ifndef FILTER_NFC_H
   2 #define FILTER_NFC_H
   3
   4 #ifdef __cplusplus
   5 extern "C" {
   6 #endif
   7
   8 struct NfcFilter1 {
   9     float base_gain, gain;
  10     float b1, a1;
  11     float z[1];
  12 };
  13 struct NfcFilter2 {
  14     float base_gain, gain;
  15     float b1, b2, a1, a2;
  16     float z[2];
  17 };
  18 struct NfcFilter3 {
  19     float base_gain, gain;
  20     float b1, b2, b3, a1, a2, a3;
  21     float z[3];
  22 };
  23
  24 typedef struct NfcFilter {
  25     struct NfcFilter1 first;
  26     struct NfcFilter2 second;
  27     struct NfcFilter3 third;
  28 } NfcFilter;
  29
  30
  31 /* NOTE:
  32  * w0 = speed_of_sound / (source_distance * sample_rate);
  33  * w1 = speed_of_sound / (control_distance * sample_rate);
  34  *
  35  * Generally speaking, the control distance should be approximately the average
  36  * speaker distance, or based on the reference delay if outputing NFC-HOA. It
  37  * must not be negative, 0, or infinite. The source distance should not be too
  38  * small relative to the control distance.
  39  */
  40
  41 void NfcFilterCreate(NfcFilter *nfc, const float w0, const float w1);
  42 void NfcFilterAdjust(NfcFilter *nfc, const float w0);
  43
  44 /* Near-field control filter for first-order ambisonic channels (1-3). */
  45 void NfcFilterProcess1(NfcFilter *nfc, float *RESTRICT dst, const float *RESTRICT src, const int count);
  46
  47 /* Near-field control filter for second-order ambisonic channels (4-8). */
  48 void NfcFilterProcess2(NfcFilter *nfc, float *RESTRICT dst, const float *RESTRICT src, const int count);
  49
  50 /* Near-field control filter for third-order ambisonic channels (9-15). */
  51 void NfcFilterProcess3(NfcFilter *nfc, float *RESTRICT dst, const float *RESTRICT src, const int count);
  52
  53 #ifdef __cplusplus
  54 } // extern "C"
  55 #endif
  56
  57 #endif /* FILTER_NFC_H */