From fc3d3c0a4f110a23335398c327ac0a4fc949d5cb Mon Sep 17 00:00:00 2001
From: Guenter  Geiger <ggeiger@users.sourceforge.net>
Date: Mon, 17 Jun 2002 10:13:57 +0000
Subject: This commit was generated by cvs2svn to compensate for changes in
 r12, which included commits to RCS files with non-trunk default branches.

svn path=/trunk/externals/ggee/; revision=13
---
 filters/lowshelf.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100755 filters/lowshelf.c

(limited to 'filters/lowshelf.c')

diff --git a/filters/lowshelf.c b/filters/lowshelf.c
new file mode 100755
index 0000000..dd925dc
--- /dev/null
+++ b/filters/lowshelf.c
@@ -0,0 +1,91 @@
+/* (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"
+
+
+
+/* ------------------- lowshelf ----------------------------*/
+
+static t_class *lowshelf_class;
+
+void lowshelf_bang(t_rbjfilter *x)
+{
+     t_atom at[5];
+     t_float omega = e_omega(x->x_freq,x->x_rate);
+     t_float A = e_A(x->x_gain);
+     t_float cs = cos(omega);
+     t_float sn = sin(omega);
+     t_float beta = e_beta(A,x->x_bw*0.01);
+
+     t_float b0 =    A*((A+1) - (A-1)*cs + beta*sn);
+     t_float b1 = 2.*A*((A-1) - (A+1)*cs);
+     t_float b2 =    A*((A+1) - (A-1)*cs - beta*sn);
+     t_float a0 =      ((A+1) + (A-1)*cs + beta*sn);
+     t_float a1 =  -2.*((A-1) + (A+1)*cs);
+     t_float a2 =      ((A+1) + (A-1)*cs - beta*sn);
+
+/*     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("lowshelf: 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 lowshelf_float(t_rbjfilter *x,t_floatarg f)
+{
+     x->x_freq = f;
+     lowshelf_bang(x);
+}
+
+
+static void *lowshelf_new(t_floatarg f,t_floatarg g,t_floatarg bw)
+{
+    t_rbjfilter *x = (t_rbjfilter *)pd_new(lowshelf_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;
+    if (g != 0.) x->x_gain = g;
+    return (x);
+}
+
+
+void lowshelf_setup(void)
+{
+    lowshelf_class = class_new(gensym("lowshelf"), (t_newmethod)lowshelf_new, 0,
+				sizeof(t_rbjfilter), 0,A_DEFFLOAT,A_DEFFLOAT,A_DEFFLOAT,0);
+    class_addbang(lowshelf_class,lowshelf_bang);
+    class_addfloat(lowshelf_class,lowshelf_float);
+}
+
+
-- 
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