add filter file

plugin/filter.cpp

@@ -0,0 +1,38 @@
+/*
+   Peacock-8 VA polysynth
+
+   Copyright 2024 Gordon JC Pearce <gordonjcp@gjcp.net>
+
+   Permission to use, copy, modify, and/or distribute this software for any
+   purpose with or without fee is hereby granted, provided that the above
+   copyright notice and this permission notice appear in all copies.
+
+   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+   WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+   MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+   SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+   OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+   CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "ic29.hpp"
+
+void Voice::filter(float *buffer, uint32_t pos, uint32_t frames) {
+    for (uint32_t i = 0; i < frames; i++) {
+        for (uint8_t ovs = 0; ovs < 4; ovs++) {
+            fb = b4;
+            // hard clip
+            if (fb > 1) fb = 1;
+            if (fb < -1) fb = -1;
+
+            fb = buffer[i+pos] - (fb * reso);
+            b1 = ((fb - b1) * cut) + b1;
+            b2 = ((b1 - b2) * cut) + b2;
+            b3 = ((b2 - b3) * cut) + b3;
+            b4 = ((b3 - b4) * cut) + b4;
+        }
+
+         buffer[i+pos] = b4;
+    }
+}