alc/filters/nfc.h

   1 #ifndef FILTER_NFC_H
   2 #define FILTER_NFC_H
   3
   4 #include <cstddef>
   5
   6 #include "alspan.h"
   7
   8
   9 struct NfcFilter1 {
  10     float base_gain, gain;
  11     float b1, a1;
  12     float z[1];
  13 };
  14 struct NfcFilter2 {
  15     float base_gain, gain;
  16     float b1, b2, a1, a2;
  17     float z[2];
  18 };
  19 struct NfcFilter3 {
  20     float base_gain, gain;
  21     float b1, b2, b3, a1, a2, a3;
  22     float z[3];
  23 };
  24 struct NfcFilter4 {
  25     float base_gain, gain;
  26     float b1, b2, b3, b4, a1, a2, a3, a4;
  27     float z[4];
  28 };
  29
  30 class NfcFilter {
  31     NfcFilter1 first;
  32     NfcFilter2 second;
  33     NfcFilter3 third;
  34     NfcFilter4 fourth;
  35
  36 public:
  37     /* NOTE:
  38      * w0 = speed_of_sound / (source_distance * sample_rate);
  39      * w1 = speed_of_sound / (control_distance * sample_rate);
  40      *
  41      * Generally speaking, the control distance should be approximately the
  42      * average speaker distance, or based on the reference delay if outputing
  43      * NFC-HOA. It must not be negative, 0, or infinite. The source distance
  44      * should not be too small relative to the control distance.
  45      */
  46
  47     void init(const float w1) noexcept;
  48     void adjust(const float w0) noexcept;
  49
  50     /* Near-field control filter for first-order ambisonic channels (1-3). */
  51     void process1(const al::span<const float> src, float *RESTRICT dst);
  52
  53     /* Near-field control filter for second-order ambisonic channels (4-8). */
  54     void process2(const al::span<const float> src, float *RESTRICT dst);
  55
  56     /* Near-field control filter for third-order ambisonic channels (9-15). */
  57     void process3(const al::span<const float> src, float *RESTRICT dst);
  58
  59     /* Near-field control filter for fourth-order ambisonic channels (16-24). */
  60     void process4(const al::span<const float> src, float *RESTRICT dst);
  61 };
  62
  63 #endif /* FILTER_NFC_H */