diff --git a/app/src/main/java/xdsopl/robot36/ColorConverter.java b/app/src/main/java/xdsopl/robot36/ColorConverter.java
index cd64aaf..d5b18e5 100644
--- a/app/src/main/java/xdsopl/robot36/ColorConverter.java
+++ b/app/src/main/java/xdsopl/robot36/ColorConverter.java
@@ -6,6 +6,8 @@ Copyright 2024 Ahmet Inan <xdsopl@gmail.com>
 
 package xdsopl.robot36;
 
+import android.graphics.Color;
+
 public final class ColorConverter {
 
 	private static int clamp(int value) {
@@ -36,6 +38,24 @@ public final class ColorConverter {
 		return 0xff000000 | (R << 16) | (G << 8) | B;
 	}
 
+	private static int[] argb2components(int argb) {
+		return new int[] { (argb >> 24) & 0xff, (argb >> 16) & 0xff, (argb >> 8) & 0xff, argb & 0xff };
+	}
+
+	public static int blend(int argbLeft, int argbRight, float ratioOfArgbRight) {
+		int[] componentsLeft = argb2components(argbLeft);
+		int[] componentsRight = argb2components(argbRight);
+		int[] output = new int[4];
+
+		ratioOfArgbRight = clamp(ratioOfArgbRight);
+
+		for (int i = 0; i < 4; i++) {
+			output[i] = clamp(Math.round(componentsLeft[i] * (1 - ratioOfArgbRight) + componentsRight[i] * ratioOfArgbRight));
+		}
+
+		return Color.argb(output[0], output[1], output[2], output[3]);
+	}
+
 	public static int GRAY(float level) {
 		return 0xff000000 | 0x00010101 * compress(level);
 	}
diff --git a/app/src/main/java/xdsopl/robot36/Demodulator.java b/app/src/main/java/xdsopl/robot36/Demodulator.java
index 2bf882a..9f48001 100644
--- a/app/src/main/java/xdsopl/robot36/Demodulator.java
+++ b/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;
diff --git a/app/src/main/java/xdsopl/robot36/MainActivity.java b/app/src/main/java/xdsopl/robot36/MainActivity.java
index 0a51384..d644c0b 100644
--- a/app/src/main/java/xdsopl/robot36/MainActivity.java
+++ b/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;
@@ -72,6 +73,7 @@ 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 +225,22 @@ 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] = ColorConverter.blend(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 +331,7 @@ 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 {