Fixed optfir for producing equiripple FIR filters. Does LPF, fixes the HPF, and adds BPF (real).

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@11537 221aa14e-8319-0410-a670-987f0aec2ac5

2 files changed, 52 insertions, 7 deletions

diff --git a/gnuradio-core/src/lib/general/gr_remez.cc b/gnuradio-core/src/lib/general/gr_remez.cc
index ca6df541b..86c2901b5 100644
--- a/gnuradio-core/src/lib/general/gr_remez.cc
+++ b/gnuradio-core/src/lib/general/gr_remez.cc
@@ -814,8 +814,10 @@ gr_remez (int order,
   if (arg_bands[0] < 0 || arg_bands[arg_bands.size () - 1] > 1)
     punt ("gr_remez: band edges must be in the range [0,1]");
 
+  // Divide by 2 to fit with the implementation that uses a
+  // sample rate of [0, 0.5] instead of [0, 1.0]
   for (int i = 0; i < 2 * numbands; i++)
-    bands[i] = arg_bands[i] / 2;		// FIXME why / 2?
+    bands[i] = arg_bands[i] / 2;
 
   LOCAL_BUFFER (double, response, numbands * 2);
   if (arg_response.size () != arg_bands.size ())
diff --git a/gnuradio-core/src/python/gnuradio/optfir.py b/gnuradio-core/src/python/gnuradio/optfir.py
index bd43fcc97..06a0eea61 100644
--- a/gnuradio-core/src/python/gnuradio/optfir.py
+++ b/gnuradio-core/src/python/gnuradio/optfir.py
@@ -1,5 +1,5 @@
 #
-# Copyright 2004,2005 Free Software Foundation, Inc.
+# Copyright 2004,2005,2009 Free Software Foundation, Inc.
 # 
 # This file is part of GNU Radio
 # 
@@ -34,25 +34,68 @@ remez = gr.remez
 
 # ----------------------------------------------------------------
 
+##  Builds a low pass filter.
+#   @param gain  Filter gain in the passband (linear)
+#   @param Fs    Sampling rate (sps)
+#   @param freq1 End of pass band (in Hz)
+#   @param freq2 Start of stop band (in Hz)
+#   @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+#   @param stopband_atten_db  Stop band attenuation in dB (should be large, >= 60)
+#   @param nextra_taps  Extra taps to use in the filter (default=2)
 def low_pass (gain, Fs, freq1, freq2, passband_ripple_db, stopband_atten_db,
-              nextra_taps=0):
+              nextra_taps=2):
     passband_dev = passband_ripple_to_dev (passband_ripple_db)
     stopband_dev = stopband_atten_to_dev (stopband_atten_db)
     desired_ampls = (gain, 0)
     (n, fo, ao, w) = remezord ([freq1, freq2], desired_ampls,
                                [passband_dev, stopband_dev], Fs)
+    # The remezord typically under-estimates the filter order, so add 2 taps by default
     taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
     return taps
 
-# FIXME high_passs is broken...
-def high_pass (Fs, freq1, freq2, stopband_atten_db, passband_ripple_db, 
-               nextra_taps=0):
-    """FIXME: broken"""
+##  Builds a band pass filter.
+#   @param gain  Filter gain in the passband (linear)
+#   @param Fs    Sampling rate (sps)
+#   @param freq1 End of stop band (in Hz)
+#   @param freq2 Start of pass band (in Hz)
+#   @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+#   @param stopband_atten_db  Stop band attenuation in dB (should be large, >= 60)
+#   @param nextra_taps  Extra taps to use in the filter (default=2)
+def band_pass (gain, Fs, freq_sb1, freq_pb1, freq_pb2, freq_sb2,
+               passband_ripple_db, stopband_atten_db,
+               nextra_taps=2):
+    passband_dev = passband_ripple_to_dev (passband_ripple_db)
+    stopband_dev = stopband_atten_to_dev (stopband_atten_db)
+    desired_ampls = (0, gain, 0)
+    desired_freqs = [freq_sb1, freq_pb1, freq_pb2, freq_sb2]
+    desired_ripple = [stopband_dev, passband_dev, stopband_dev]
+    (n, fo, ao, w) = remezord (desired_freqs, desired_ampls,
+                               desired_ripple, Fs)
+    # The remezord typically under-estimates the filter order, so add 2 taps by default
+    taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
+    return taps
+
+##  Builds a high pass filter.
+#   @param gain  Filter gain in the passband (linear)
+#   @param Fs    Sampling rate (sps)
+#   @param freq1 End of stop band (in Hz)
+#   @param freq2 Start of pass band (in Hz)
+#   @param passband_ripple_db Pass band ripple in dB (should be small, < 1)
+#   @param stopband_atten_db  Stop band attenuation in dB (should be large, >= 60)
+#   @param nextra_taps  Extra taps to use in the filter (default=2)
+def high_pass (gain, Fs, freq1, freq2, passband_ripple_db, stopband_atten_db,
+               nextra_taps=2):
     passband_dev = passband_ripple_to_dev (passband_ripple_db)
     stopband_dev = stopband_atten_to_dev (stopband_atten_db)
     desired_ampls = (0, 1)
     (n, fo, ao, w) = remezord ([freq1, freq2], desired_ampls,
                                [stopband_dev, passband_dev], Fs)
+    # For a HPF, we need to use an odd number of taps
+    # In gr.remez, ntaps = n+1, so n must be even
+    if((n+nextra_taps)%2 == 1):
+        n += 1
+        
+    # The remezord typically under-estimates the filter order, so add 2 taps by default
     taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
     return taps