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authorGuenter Geiger <ggeiger@users.sourceforge.net>2002-06-17 10:13:57 +0000
committerGuenter Geiger <ggeiger@users.sourceforge.net>2002-06-17 10:13:57 +0000
commitfc3d3c0a4f110a23335398c327ac0a4fc949d5cb (patch)
tree1849d6afbe34cee9cec97bdb2295401f5126870b /filters/lowpass.c
This commit was generated by cvs2svn to compensate for changes in r12,svn2git-root
which included commits to RCS files with non-trunk default branches. svn path=/trunk/externals/ggee/; revision=13
Diffstat (limited to 'filters/lowpass.c')
-rwxr-xr-xfilters/lowpass.c89
1 files changed, 89 insertions, 0 deletions
diff --git a/filters/lowpass.c b/filters/lowpass.c
new file mode 100755
index 0000000..4e1b2b9
--- /dev/null
+++ b/filters/lowpass.c
@@ -0,0 +1,89 @@
+/* (C) Guenter Geiger <geiger@epy.co.at> */
+
+
+/*
+
+ These filter coefficients computations are taken from
+ http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt
+
+ written by Robert Bristow-Johnson
+
+*/
+
+#include <m_pd.h>
+#ifdef NT
+#pragma warning( disable : 4244 )
+#pragma warning( disable : 4305 )
+#endif
+#include <math.h>
+#include "filters.h"
+
+
+
+/* ------------------- lowpass ----------------------------*/
+
+static t_class *lowpass_class;
+
+void lowpass_bang(t_rbjfilter *x)
+{
+ t_atom at[5];
+ t_float omega = e_omega(x->x_freq,x->x_rate);
+ t_float alpha = e_alpha(x->x_bw*0.01,omega);
+ t_float b1 = 1 - cos(omega);
+ t_float b0 = b1/2.;
+ t_float b2 = b0;
+ t_float a0 = 1 + alpha;
+ t_float a1 = -2.*cos(omega);
+ t_float a2 = 1 - alpha;
+
+/* post("bang %f %f %f",x->x_freq, x->x_gain, x->x_bw); */
+
+ if (!check_stability(-a1/a0,-a2/a0,b0/a0,b1/a0,b2/a0)) {
+ post("lowpass: filter unstable -> resetting");
+ a0=1.;a1=0.;a2=0.;
+ b0=1.;b1=0.;b2=0.;
+ }
+
+ SETFLOAT(at,-a1/a0);
+ SETFLOAT(at+1,-a2/a0);
+ SETFLOAT(at+2,b0/a0);
+ SETFLOAT(at+3,b1/a0);
+ SETFLOAT(at+4,b2/a0);
+
+ outlet_list(x->x_obj.ob_outlet,&s_list,5,at);
+}
+
+
+void lowpass_float(t_rbjfilter *x,t_floatarg f)
+{
+ x->x_freq = f;
+ lowpass_bang(x);
+}
+
+
+static void *lowpass_new(t_floatarg f,t_floatarg bw)
+{
+ t_rbjfilter *x = (t_rbjfilter *)pd_new(lowpass_class);
+
+ x->x_rate = 44100.0;
+ outlet_new(&x->x_obj,&s_float);
+/* floatinlet_new(&x->x_obj, &x->x_gain); */
+ floatinlet_new(&x->x_obj, &x->x_bw);
+
+ if (f > 0.) x->x_freq = f;
+ if (bw > 0.) x->x_bw = bw;
+ return (x);
+}
+
+
+void lowpass_setup(void)
+{
+ lowpass_class = class_new(gensym("lowpass"), (t_newmethod)lowpass_new, 0,
+ sizeof(t_rbjfilter), 0,A_DEFFLOAT,A_DEFFLOAT,0);
+ class_addbang(lowpass_class,lowpass_bang);
+ class_addfloat(lowpass_class,lowpass_float);
+}
+
+
+
+