Added frequency markers to waterfall

app/src/main/java/xdsopl/robot36/Demodulator.java

@@ -33,9 +33,11 @@ public class Demodulator {
 	public int syncPulseOffset;
 	public float frequencyOffset;
 
+	public static final double syncPulseFrequency = 1200;
+	public static final double blackFrequency = 1500;
+	public static final double whiteFrequency = 2300;
+
 	Demodulator(int sampleRate) {
-		double blackFrequency = 1500;
-		double whiteFrequency = 2300;
 		double scanLineBandwidth = whiteFrequency - blackFrequency;
 		frequencyModulation = new FrequencyModulation(scanLineBandwidth, sampleRate);
 		double syncPulse5msSeconds = 0.005;
@@ -65,7 +67,6 @@ public class Demodulator {
 			baseBandLowPass.taps[i] = (float) (kaiser.window(2.0, i, baseBandLowPass.length) * Filter.lowPass(cutoffFrequency, sampleRate, i, baseBandLowPass.length));
 		double centerFrequency = (lowestFrequency + highestFrequency) / 2;
 		baseBandOscillator = new Phasor(-centerFrequency, sampleRate);
-		double syncPulseFrequency = 1200;
 		syncPulseFrequencyValue = (float) ((syncPulseFrequency - centerFrequency) * 2 / scanLineBandwidth);
 		syncPulseFrequencyTolerance = (float) (50 * 2 / scanLineBandwidth);
 		double syncPorchFrequency = 1500;

app/src/main/java/xdsopl/robot36/MainActivity.java

@@ -15,6 +15,7 @@ import android.content.SharedPreferences;
 import android.content.pm.PackageManager;
 import android.content.res.Configuration;
 import android.graphics.Bitmap;
+import android.graphics.Color;
 import android.media.AudioFormat;
 import android.media.AudioRecord;
 import android.media.MediaRecorder;
@@ -43,6 +44,7 @@ import androidx.appcompat.app.AppCompatDelegate;
 import androidx.appcompat.widget.ShareActionProvider;
 import androidx.core.app.ActivityCompat;
 import androidx.core.content.ContextCompat;
+import androidx.core.graphics.ColorUtils;
 import androidx.core.graphics.Insets;
 import androidx.core.os.LocaleListCompat;
 import androidx.core.view.MenuItemCompat;
@@ -72,6 +74,7 @@ public class MainActivity extends AppCompatActivity {
 	private ImageView peakMeterView;
 	private PixelBuffer imageBuffer;
 	private ShortTimeFourierTransform stft;
+	private final int binWidthHz = 10;
 	private short[] shortBuffer;
 	private float[] recordBuffer;
 	private AudioRecord audioRecord;
@@ -223,8 +226,22 @@ public class MainActivity extends AppCompatActivity {
 				double lowest = Math.log(1e-9);
 				double highest = Math.log(1);
 				double range = highest - lowest;
+				int lowestBin = 14;
 				for (int i = 0; i < stride; ++i)
-					waterfallPlotBuffer.pixels[line + i] = rainbow((Math.log(stft.power[i + 14]) - lowest) / range);
+					waterfallPlotBuffer.pixels[line + i] = rainbow((Math.log(stft.power[i + lowestBin]) - lowest) / range);
+
+				int[] markerFrequencies = new int[] {
+						(int)Demodulator.syncPulseFrequency,
+						(int)Demodulator.blackFrequency,
+						(int)Demodulator.whiteFrequency,
+				};
+				for (int freq: markerFrequencies) {
+					int marker = freq / binWidthHz - lowestBin;
+					waterfallPlotBuffer.pixels[line + marker - 1] = Color.BLACK;
+					waterfallPlotBuffer.pixels[line + marker] = ColorUtils.blendARGB(waterfallPlotBuffer.pixels[line + marker], Color.GREEN, 0.8f);
+					waterfallPlotBuffer.pixels[line + marker + 1] = Color.BLACK;
+				}
+
 				System.arraycopy(waterfallPlotBuffer.pixels, line, waterfallPlotBuffer.pixels, line + stride * (waterfallPlotBuffer.height / 2), stride);
 			}
 		}
@@ -315,7 +332,7 @@ public class MainActivity extends AppCompatActivity {
 				if (rateChanged) {
 					decoder = new Decoder(scopeBuffer, imageBuffer, getString(R.string.raw_mode), recordRate);
 					decoder.setMode(currentMode);
-					stft = new ShortTimeFourierTransform(recordRate / 10, 3);
+					stft = new ShortTimeFourierTransform(recordRate / binWidthHz, 3);
 				}
 				startListening();
 			} else {