Add sample rate control

re #10

spectrogram.cpp

@@ -9,6 +9,7 @@
 
 Spectrogram::Spectrogram()
 {
+	sampleRate = 8000000;
 	setFFTSize(1024);
 	zoomLevel = 0;
 	powerMax = 0.0f;
@@ -161,6 +162,12 @@ void Spectrogram::getLine(float *dest, int y)
 	}
 }
 
+void Spectrogram::setSampleRate(int rate)
+{
+	sampleRate = rate;
+	update();
+}
+
 void Spectrogram::setFFTSize(int size)
 {
 	fftSize = size;