Added 3 term Blackman window to FFTWindow and use it as default in FFT filter

plugins/channelrx/demodchirpchat/chirpchatdemodgui.ui

@@ -331,6 +331,11 @@
           <string>Kai</string>
          </property>
         </item>
+        <item>
+         <property name="text">
+          <string>Black</string>
+         </property>
+        </item>
        </widget>
       </item>
       <item>

sdrbase/dsp/fftfilt.cpp

@@ -112,7 +112,7 @@ fftfilt::~fftfilt()
 	if (ovlbuf) delete [] ovlbuf;
 }
 
-void fftfilt::create_filter(float f1, float f2)
+void fftfilt::create_filter(float f1, float f2, FFTWindow::Function wf)
 {
 	// initialize the filter to zero
 	std::fill(filter, filter + flen, cmplx{0, 0});
@@ -135,8 +135,12 @@ void fftfilt::create_filter(float f1, float f2)
 	if (b_highpass && f2 < f1)
 		filter[flen2 / 2] += 1;
 
-	for (int i = 0; i < flen2; i++)
+    FFTWindow fwin;
-		filter[i] *= _blackman(i, flen2);
+    fwin.create(wf, flen2);
+    fwin.apply(filter);
+
+	// for (int i = 0; i < flen2; i++)
+	// 	filter[i] *= _blackman(i, flen2);
 
 	fft->ComplexFFT(filter); // filter was expressed in the time domain (impulse response)
 
@@ -153,16 +157,20 @@ void fftfilt::create_filter(float f1, float f2)
 }
 
 // Double the size of FFT used for equivalent SSB filter or assume FFT is half the size of the one used for SSB
-void fftfilt::create_dsb_filter(float f2)
+void fftfilt::create_dsb_filter(float f2, FFTWindow::Function wf)
 {
 	// initialize the filter to zero
 	std::fill(filter, filter + flen, cmplx{0, 0});
 
 	for (int i = 0; i < flen2; i++) {
 		filter[i] = fsinc(f2, i, flen2);
-		filter[i] *= _blackman(i, flen2);
+		// filter[i] *= _blackman(i, flen2);
 	}
 
+    FFTWindow fwin;
+    fwin.create(wf, flen2);
+    fwin.apply(filter);
+
 	fft->ComplexFFT(filter); // filter was expressed in the time domain (impulse response)
 
 	// normalize the output filter for unity gain
@@ -179,7 +187,7 @@ void fftfilt::create_dsb_filter(float f2)
 
 // Double the size of FFT used for equivalent SSB filter or assume FFT is half the size of the one used for SSB
 // used with runAsym for in band / opposite band asymmetrical filtering. Can be used for vestigial sideband modulation.
-void fftfilt::create_asym_filter(float fopp, float fin)
+void fftfilt::create_asym_filter(float fopp, float fin, FFTWindow::Function wf)
 {
     // in band
     // initialize the filter to zero
@@ -187,9 +195,13 @@ void fftfilt::create_asym_filter(float fopp, float fin)
 
     for (int i = 0; i < flen2; i++) {
         filter[i] = fsinc(fin, i, flen2);
-        filter[i] *= _blackman(i, flen2);
+        // filter[i] *= _blackman(i, flen2);
     }
 
+    FFTWindow fwin;
+    fwin.create(wf, flen2);
+    fwin.apply(filter);
+
     fft->ComplexFFT(filter); // filter was expressed in the time domain (impulse response)
 
     // normalize the output filter for unity gain
@@ -209,9 +221,10 @@ void fftfilt::create_asym_filter(float fopp, float fin)
 
     for (int i = 0; i < flen2; i++) {
         filterOpp[i] = fsinc(fopp, i, flen2);
-        filterOpp[i] *= _blackman(i, flen2);
+        // filterOpp[i] *= _blackman(i, flen2);
     }
 
+    fwin.apply(filterOpp);
     fft->ComplexFFT(filterOpp); // filter was expressed in the time domain (impulse response)
 
     // normalize the output filter for unity gain

sdrbase/dsp/fftfilt.h

@@ -9,6 +9,7 @@
 #include <cmath>
 
 #include "gfft.h"
+#include "fftwindow.h"
 #include "export.h"
 
 //----------------------------------------------------------------------
@@ -25,9 +26,9 @@ public:
 	~fftfilt();
 // f1 < f2 ==> bandpass
 // f1 > f2 ==> band reject
-	void create_filter(float f1, float f2);
+	void create_filter(float f1, float f2, FFTWindow::Function wf = FFTWindow::Blackman);
-	void create_dsb_filter(float f2);
+	void create_dsb_filter(float f2, FFTWindow::Function wf = FFTWindow::Blackman);
-    void create_asym_filter(float fopp, float fin); //!< two different filters for in band and opposite band
+    void create_asym_filter(float fopp, float fin, FFTWindow::Function wf = FFTWindow::Blackman); //!< two different filters for in band and opposite band
     void create_rrc_filter(float fb, float a); //!< root raised cosine. fb is half the band pass
 
 	int noFilt(const cmplx& in, cmplx **out);

sdrbase/dsp/fftwindow.cpp

@@ -51,7 +51,7 @@ void FFTWindow::create(Function function, int n)
 		return;
 	}
 
-	switch(function) {
+	switch (function) {
 		case Flattop:
 			wFunc = flatTop;
 			break;
@@ -72,6 +72,10 @@ void FFTWindow::create(Function function, int n)
 			wFunc = hanning;
 			break;
 
+        case Blackman:
+            wFunc = blackman;
+            break;
+
 		case Rectangle:
 		default:
 			wFunc = rectangle;

sdrbase/dsp/fftwindow.h

@@ -33,7 +33,8 @@ public:
 		Hamming,
 		Hanning,
 		Rectangle,
-		Kaiser
+		Kaiser,
+        Blackman
 	};
 
 	FFTWindow();
@@ -70,6 +71,11 @@ private:
 		return (0.35875 - 0.48829 * cos((2.0 * M_PI * i) / n) + 0.14128 * cos((4.0 * M_PI * i) / n) - 0.01168 * cos((6.0 * M_PI * i) / n)) * 2.79;
 	}
 
+    static inline Real blackman(Real n, Real i)
+    {
+        return (0.42438 - 0.49734 * cos(2.0 * M_PI * i / n) + 0.078279 * cos(4.0 * M_PI * i / n)) * 2.37;
+    }
+
 	static inline Real hamming(Real n, Real i)
 	{
 		// amplitude correction = 1.855, energy correction = 1.586

sdrgui/gui/glspectrumgui.ui

@@ -101,6 +101,11 @@
          <string>Kai</string>
         </property>
        </item>
+       <item>
+        <property name="text">
+         <string>Black</string>
+        </property>
+       </item>
       </widget>
      </item>
      <item>