initHEADmain

1 files changed, 202 insertions, 0 deletions

diff --git a/mod/biquad.c b/mod/biquad.c
new file mode 100644
index 0000000..6591d87
--- /dev/null
+++ b/mod/biquad.c
@@ -0,0 +1,202 @@
+/*
+ * melisma - extensible and scriptable audio engine
+ * Copyright (C) 2026  Ludvig Gunne Lindström
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include <math.h>
+#include <lauxlib.h>
+#include "melisma.h"
+#include "mutil.h"
+
+#define LOWPASS_TYPENAME "biquad LPF"
+#define LOWPASS_DEFAULT_CUTOFF 4000
+#define LOWPASS_DEFAULT_RESONANCE 0.5
+
+struct biquad;
+
+typedef void (*recomp_fn)(struct biquad*);
+
+struct biquad
+{
+	ml_channel *out;
+	recomp_fn   recomp;
+	double      x_1,x_2,y_1,y_2;
+	double      xc_0,xc_1,xc_2;
+	double      yc_1,yc_2;
+	double      Fs;
+	double      f0;
+	double      Q;
+};
+
+static inline void lowpass_recomp(struct biquad *bq)
+{
+	double w0,cosw0,sinw0,alpha,b0,b1,b2,a0,a1,a2;
+	w0 = 2*M_PI*bq->f0/bq->Fs;
+	cosw0 = cos(w0);
+	sinw0 = sin(w0);
+	alpha = sinw0/(2*bq->Q);
+	b0 = (1 - cosw0)/2;
+	b1 = 1 - cosw0;
+	b2 = (1 - cosw0)/2;
+	a0 = 1 + alpha;
+	a1 = -2*cosw0;
+	a2 = 1 - alpha;
+	bq->xc_0 = b0/a0;
+	bq->xc_1 = b1/a0;
+	bq->xc_2 = b2/a0;
+	bq->yc_1 = a1/a0;
+	bq->yc_2 = a2/a0;
+}
+
+static void proc(const ml_proc_args *args)
+{
+	struct biquad bq = *(struct biquad*) args->userp;
+
+	float *x = args->in[0];
+	float *y = args->out[0];
+
+	for (size_t i = 0; i < args->nframes; i++)
+	{
+		y[i] = bq.xc_0*x[i]
+		     + bq.xc_1*bq.x_1
+		     + bq.xc_2*bq.x_2
+		     - bq.yc_1*bq.y_1
+		     - bq.yc_2*bq.y_2;
+
+		bq.x_2 = bq.x_1;
+		bq.x_1 = x[i];
+		bq.y_2 = bq.y_1;
+		bq.y_1 = y[i];
+	}
+
+	*(struct biquad*) args->userp = bq;
+}
+
+static int l_lowpass_init(lua_State *s)
+{
+	ml_channel *src = mutil_get_channel(s,1);
+
+	struct biquad *bq = calloc(1,sizeof(*bq));
+	bq->recomp = lowpass_recomp;
+	bq->Fs = ml_sample_rate();
+	bq->f0 = LOWPASS_DEFAULT_CUTOFF;
+	bq->Q = LOWPASS_DEFAULT_RESONANCE;
+	bq->recomp(bq);
+
+	ml_node *node = ml_create_node(proc,bq);
+	ml_label_node(node,"lowpass");
+
+	ml_channel *dst = ml_add_input(node);
+	ml_connect(src,dst);
+
+	bq->out = ml_add_output(node);
+
+	*(void**) lua_newuserdata(s,sizeof(void*)) = bq;
+	luaL_setmetatable(s,LOWPASS_TYPENAME);
+
+	return 1;
+}
+
+static int l_lowpass_resonance(lua_State *s)
+{
+	struct biquad *bq = *(void**) luaL_checkudata(s,1,LOWPASS_TYPENAME);
+	bq->Q = luaL_checknumber(s,2);
+	bq->recomp(bq);
+	*(void**) lua_newuserdata(s,sizeof(void*)) = bq;
+	luaL_setmetatable(s,LOWPASS_TYPENAME);
+	return 1;
+}
+
+static int l_lowpass_cutoff(lua_State *s)
+{
+	struct biquad *bq = *(void**) luaL_checkudata(s,1,LOWPASS_TYPENAME);
+	bq->f0 = luaL_checknumber(s,2);
+	bq->recomp(bq);
+	*(void**) lua_newuserdata(s,sizeof(void*)) = bq;
+	luaL_setmetatable(s,LOWPASS_TYPENAME);
+	return 1;
+}
+
+static int l_lowpass_out(lua_State *s)
+{
+	struct biquad *bq = *(void**) luaL_checkudata(s,1,LOWPASS_TYPENAME);
+	*(void**) lua_newuserdata(s,sizeof(void*)) = bq->out;
+	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
+	return 1;
+}
+
+int luaopen_melisma_biquad(lua_State *s)
+{
+/*** Digital biquad filters.
+@module biquad
+*/
+	lua_newtable(s);
+	int tbl = lua_gettop(s);
+
+/*** Lowpass filter.
+@type biquad.lowpass
+@usage
+
+	local mbiquad = require 'melisma.biquad'
+	local input = ...
+	local lowpass = mbiquad.lowpass.init(node, 2000, 0.6)
+	lowpass:resonance(1000)
+	lowpass:cutoff(0.25)
+*/
+	lua_newtable(s);
+	int lowpass_tbl = lua_gettop(s);
+
+/*** Create a lowpass filter.
+@static
+@function init
+@tparam channel input Input signal.
+@treturn biquad.lowpass The newly created lowpass filter.
+*/
+	lua_pushcfunction(s,l_lowpass_init);
+	lua_setfield(s,lowpass_tbl,"init");
+
+/*** Set filter resonance.
+@function lowpass:resonance
+@tparam number res Resonance.
+*/
+	lua_pushcfunction(s,l_lowpass_resonance);
+	lua_setfield(s,lowpass_tbl,"resonance");
+
+
+/*** Set filter cutoff frequency.
+@function lowpass:cutoff
+@tparam number cut Cutoff frequency.
+*/
+	lua_pushcfunction(s,l_lowpass_cutoff);
+	lua_setfield(s,lowpass_tbl,"cutoff");
+
+	lua_pushcfunction(s,l_lowpass_out);
+	lua_setfield(s,lowpass_tbl,MUTIL_OUTPUT_CHANNEL_FUNCTION);
+
+	luaL_newmetatable(s,LOWPASS_TYPENAME);
+	int lowpass_mt = lua_gettop(s);
+
+	lua_pushvalue(s,lowpass_tbl);
+	lua_setfield(s,lowpass_mt,"__index");
+
+	lua_pushvalue(s,lowpass_tbl);
+	lua_setfield(s,tbl,"lowpass");
+
+	lua_settop(s,tbl);
+	return 1;
+}