From 756de6fee0abbb270f862b17a3655c5f3d76f626 Mon Sep 17 00:00:00 2001
From: "Robin. P. Clark" <robin@energytechnologycontrol.com>
Date: Mon, 16 Sep 2019 14:30:42 +0100
Subject: [PATCH] some zeros filters

---
 freq_analysis.c | 41 ++++++++++++++++++++++++++++++++---------
 1 file changed, 32 insertions(+), 9 deletions(-)

diff --git a/freq_analysis.c b/freq_analysis.c
index 9210845..3b4b440 100644
--- a/freq_analysis.c
+++ b/freq_analysis.c
@@ -94,16 +94,39 @@ main () {
 	}
 
 	// simple lag filter
-	// xz[0] = 0.125;
-	// yp[0] = 1.0;
-	// yp[1] = -0.875;
-	//
-	//
-	//simple 7/8th lag filter squared
-	xz[0] = (0.125*0.125);
+	xz[0] = 0.125;
 	yp[0] = 1.0;
-	yp[1] = -(2.0*0.875);
-	yp[2] = (0.875*0.875); 
+	yp[1] = -0.875;
+
+
+	// simple 7/8th lag filter squared
+	//
+	// xz[0] = (0.125*0.125);
+	// yp[0] = 1.0;
+	// yp[1] = -(2.0*0.875);
+	// yp[2] = (0.875*0.875); 
+
+	// simple bandpass
+	// (Z-1)(Z+1) = Z^2-1
+	// xz[0] = 1.0;
+	// xz[1] = 0.0;
+	// xz[2] = -1.0;
+	// yp[0] = 1.0;
+
+        // peaky x4 bandpass, no d.c. no high freq near nyquist.	
+	// (Z^2-1)^2
+	// 
+	// xz[0] = 1.0;
+	// xz[1] = 0.0;
+	// xz[2] = -2.0;
+	// xz[3] = 0.0;
+	// xz[4] = 1.0;
+	// yp[0] = 1.0;
+	// yp[1] = 0.0;
+	// yp[2] = 0.0;
+	//
+	
+	
 
 	for (i=0;i<NYQUIST;i++) {