1 files changed, 58 insertions, 0 deletions
diff --git a/alc/filters/nfc.h b/alc/filters/nfc.h
new file mode 100644
index 00000000..b656850a
--- /dev/null
+++ b/alc/filters/nfc.h
@@ -0,0 +1,58 @@
+#ifndef FILTER_NFC_H
+#define FILTER_NFC_H
+
+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];
+};
+struct NfcFilter4 {
+    float base_gain, gain;
+    float b1, b2, b3, b4, a1, a2, a3, a4;
+    float z[4];
+};
+
+class NfcFilter {
+    NfcFilter1 first;
+    NfcFilter2 second;
+    NfcFilter3 third;
+    NfcFilter4 fourth;
+
+public:
+    /* 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 init(const float w1) noexcept;
+    void adjust(const float w0) noexcept;
+
+    /* Near-field control filter for first-order ambisonic channels (1-3). */
+    void process1(float *RESTRICT dst, const float *RESTRICT src, const int count);
+
+    /* Near-field control filter for second-order ambisonic channels (4-8). */
+    void process2(float *RESTRICT dst, const float *RESTRICT src, const int count);
+
+    /* Near-field control filter for third-order ambisonic channels (9-15). */
+    void process3(float *RESTRICT dst, const float *RESTRICT src, const int count);
+
+    /* Near-field control filter for fourth-order ambisonic channels (16-24). */
+    void process4(float *RESTRICT dst, const float *RESTRICT src, const int count);
+};
+
+#endif /* FILTER_NFC_H */