diff --git a/src/main/java/io/github/dsheirer/dsp/filter/FilterFactory.java b/src/main/java/io/github/dsheirer/dsp/filter/FilterFactory.java
index 235f8581..6c83b7d4 100644
--- a/src/main/java/io/github/dsheirer/dsp/filter/FilterFactory.java
+++ b/src/main/java/io/github/dsheirer/dsp/filter/FilterFactory.java
@@ -1,25 +1,21 @@
-/*******************************************************************************
- * SDR Trunk
- * Copyright (C) 2014,2015 Dennis Sheirer
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2021 Dennis Sheirer
*
- * Root Raised Cosine filter designer:
- * Copyright 2002,2007,2008,2012,2013 Free Software Foundation, Inc.
- * http://gnuradio.org/redmine/projects/gnuradio/repository/changes/gr-filter
- * /lib/firdes.cc?rev=435b1d166f0c7092bbd5e1f788e75dbb6ade3a4b
+ * 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 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.
*
- * 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
- ******************************************************************************/
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see
+ * ****************************************************************************
+ */
package io.github.dsheirer.dsp.filter;
import io.github.dsheirer.dsp.filter.design.FilterDesignException;
@@ -31,7 +27,7 @@ import org.jtransforms.fft.FloatFFT_1D;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
-import java.util.Arrays;
+import java.text.DecimalFormat;
import java.util.Set;
import java.util.TreeSet;
@@ -1001,6 +997,44 @@ public class FilterFactory
return coefficients;
}
+ /**
+ * Creates a symmetrical half-band filter where all odd-indexed coefficients except center are zero
+ * valued.
+ * @param length N is odd where m is an integer multiple in the formula: N = 4m + 3 (e.g. 7, 11, 15, etc.)
+ * @param windowType to apply to the filter.
+ * @return coefficients
+ */
+ public static double[] getHalfBand(int length, Window.WindowType windowType)
+ {
+ if((length - 3) % 4 != 0)
+ {
+ throw new IllegalArgumentException("Half Band filter length (N) must be an odd length where m must be an " +
+ "integer multiple in (N=4m+3), e.g. 7, 11, 15, etc");
+ }
+
+ double[] window = Window.getWindow(windowType, length);
+ double[] taps = new double[length];
+
+ int halfLength = length / 2;
+
+ for(int x = 0; x < length; x++)
+ {
+ int offset = x - halfLength;
+
+ if(offset == 0)
+ {
+ taps[x] = 0.5f; //No window here - window coefficient should be 1.0 anyway
+ }
+ else if((x % 2) == 0)
+ {
+ //Only calculate the even-index taps, leaving odd-index taps at default value of zero
+ taps[x] = (float)((Math.sin(offset * Math.PI / 2) / (offset * Math.PI)) * window[x]);
+ }
+ }
+
+ return taps;
+ }
+
/**
* Compares two doubles for equals and avoids any rounding error that are present.
*
@@ -1015,17 +1049,17 @@ public class FilterFactory
public static void main(String[] args)
{
- float[] taps = null;
+ DecimalFormat df = new DecimalFormat("0.000000");
- try
+ int length = 15;
+
+ double [] taps = FilterFactory.getHalfBand(length, Window.WindowType.HAMMING);
+
+ for(int x = 0; x < length; x++)
{
- taps = FilterFactory.getSincM2Channelizer(12500.0, 800, 9, true);
- }
- catch(FilterDesignException fde)
- {
- mLog.error("Error", fde);
+ mLog.debug("Tap: " + x + " Value: " + df.format(taps[x]));
}
- mLog.debug("Done: " + Arrays.toString(taps));
+ mLog.debug("Done!");
}
}
diff --git a/src/main/java/io/github/dsheirer/dsp/filter/Window.java b/src/main/java/io/github/dsheirer/dsp/filter/Window.java
index b67b459a..7ccea3f0 100644
--- a/src/main/java/io/github/dsheirer/dsp/filter/Window.java
+++ b/src/main/java/io/github/dsheirer/dsp/filter/Window.java
@@ -1,39 +1,22 @@
-/*******************************************************************************
- * sdr-trunk
- * Copyright (C) 2014-2018 Dennis Sheirer
- *
- * 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
- *
- ******************************************************************************/
-
/*
- * Kaiser Window design methods: getKaiser(), getKaiserBeta() and getBesselZerothOrder() with minor naming changes were
- * adopted from:
+ * *****************************************************************************
+ * Copyright (C) 2014-2021 Dennis Sheirer
*
- * https://github.com/rjeschke/neetutils-base/blob/master/src/main/java/com/github/rjeschke/neetutils/audio/FIRUtils.java
+ * 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.
*
- * Copyright (C) 2012 René Jeschke
+ * 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.
*
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see
+ * ****************************************************************************
*/
+
package io.github.dsheirer.dsp.filter;
import org.apache.commons.math3.util.FastMath;
@@ -294,13 +277,9 @@ public class Window
{
double[] coefficients = new double[length];
- double a0 = 0.54;
- double a1 = 0.46;
- double denominator = length;
-
for(int x = 0; x < length; x++)
{
- coefficients[x] = a0 - (a1 * FastMath.cos(TWO_PI * (double)x / denominator));
+ coefficients[x] = 0.54 - (0.46 * FastMath.cos((TWO_PI * x) / (length - 1)));
}
return coefficients;
@@ -316,13 +295,9 @@ public class Window
{
double[] coefficients = new double[length];
- double a0 = 0.5;
- double a1 = 0.5;
- double denominator = length;
-
for(int x = 0; x < length; x++)
{
- coefficients[x] = a0 - (a1 * FastMath.cos(TWO_PI * (double)x / denominator));
+ coefficients[x] = 0.5 - (0.5 * FastMath.cos(TWO_PI * (double)x / (length - 1)));
}
return coefficients;