alc/filters/nfc.h

   1 #ifndef FILTER_NFC_H
   2 #define FILTER_NFC_H
   3
   4 #include <cstddef>
   5
   6
   7 struct NfcFilter1 {
   8     float base_gain, gain;
   9     float b1, a1;
  10     float z[1];
  11 };
  12 struct NfcFilter2 {
  13     float base_gain, gain;
  14     float b1, b2, a1, a2;
  15     float z[2];
  16 };
  17 struct NfcFilter3 {
  18     float base_gain, gain;
  19     float b1, b2, b3, a1, a2, a3;
  20     float z[3];
  21 };
  22 struct NfcFilter4 {
  23     float base_gain, gain;
  24     float b1, b2, b3, b4, a1, a2, a3, a4;
  25     float z[4];
  26 };
  27
  28 class NfcFilter {
  29     NfcFilter1 first;
  30     NfcFilter2 second;
  31     NfcFilter3 third;
  32     NfcFilter4 fourth;
  33
  34 public:
  35     /* NOTE:
  36      * w0 = speed_of_sound / (source_distance * sample_rate);
  37      * w1 = speed_of_sound / (control_distance * sample_rate);
  38      *
  39      * Generally speaking, the control distance should be approximately the
  40      * average speaker distance, or based on the reference delay if outputing
  41      * NFC-HOA. It must not be negative, 0, or infinite. The source distance
  42      * should not be too small relative to the control distance.
  43      */
  44
  45     void init(const float w1) noexcept;
  46     void adjust(const float w0) noexcept;
  47
  48     /* Near-field control filter for first-order ambisonic channels (1-3). */
  49     void process1(float *RESTRICT dst, const float *RESTRICT src, const size_t count);
  50
  51     /* Near-field control filter for second-order ambisonic channels (4-8). */
  52     void process2(float *RESTRICT dst, const float *RESTRICT src, const size_t count);
  53
  54     /* Near-field control filter for third-order ambisonic channels (9-15). */
  55     void process3(float *RESTRICT dst, const float *RESTRICT src, const size_t count);
  56
  57     /* Near-field control filter for fourth-order ambisonic channels (16-24). */
  58     void process4(float *RESTRICT dst, const float *RESTRICT src, const size_t count);
  59 };
  60
  61 #endif /* FILTER_NFC_H */