Add an NFC filter implementation

1 files changed, 37 insertions, 0 deletions

diff --git a/Alc/nfcfilter.h b/Alc/nfcfilter.h
new file mode 100644
index 00000000..199849fb
--- /dev/null
+++ b/Alc/nfcfilter.h
@@ -0,0 +1,37 @@
+#ifndef NFCFILTER_H
+#define NFCFILTER_H
+
+#include "alMain.h"
+
+typedef struct NfcFilter {
+    float g;
+    float coeffs[MAX_AMBI_ORDER*2 + 1];
+    float history[MAX_AMBI_ORDER];
+} NfcFilter;
+
+/* 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.
+ */
+
+/* Near-field control filter for first-order ambisonic channels (1-3). */
+void NfcFilterCreate1(NfcFilter *nfc, const float w0, const float w1);
+void NfcFilterAdjust1(NfcFilter *nfc, const float w0);
+void NfcFilterUpdate1(NfcFilter *nfc, float *restrict dst, const float *restrict src, const int count);
+
+/* Near-field control filter for second-order ambisonic channels (4-8). */
+void NfcFilterCreate2(NfcFilter *nfc, const float w0, const float w1);
+void NfcFilterAdjust2(NfcFilter *nfc, const float w0);
+void NfcFilterUpdate2(NfcFilter *nfc, float *restrict dst, const float *restrict src, const int count);
+
+/* Near-field control filter for third-order ambisonic channels (9-15). */
+void NfcFilterCreate3(NfcFilter *nfc, const float w0, const float w1);
+void NfcFilterAdjust3(NfcFilter *nfc, const float w0);
+void NfcFilterUpdate3(NfcFilter *nfc, float *restrict dst, const float *restrict src, const int count);
+
+#endif /* NFCFILTER_H */