Alc/filters/nfc.h

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