diff --git a/app/src/main/java/xdsopl/robot36/Decoder.java b/app/src/main/java/xdsopl/robot36/Decoder.java
index 75eb167..31c1711 100644
--- a/app/src/main/java/xdsopl/robot36/Decoder.java
+++ b/app/src/main/java/xdsopl/robot36/Decoder.java
@@ -52,7 +52,9 @@ public class Decoder {
 		double scanLineMaxSeconds = 7;
 		int scanLineMaxSamples = (int) Math.round(scanLineMaxSeconds * sampleRate);
 		scanLineBuffer = new float[scanLineMaxSamples];
-		scratchBuffer = new float[sampleRate];
+		double scratchBufferSeconds = 1.1;
+		int scratchBufferSamples = (int) Math.round(scratchBufferSeconds * sampleRate);
+		scratchBuffer = new float[scratchBufferSamples];
 		int scanLineCount = 4;
 		last5msScanLines = new int[scanLineCount];
 		last9msScanLines = new int[scanLineCount];
@@ -160,10 +162,12 @@ public class Decoder {
 		if (lines[0] == 0)
 			return false;
 		double mean = scanLineMean(lines);
+		int scanLineSamples = (int) Math.round(mean);
+		if (scanLineSamples > scratchBuffer.length)
+			return false;
 		if (scanLineStdDev(lines, mean) > scanLineToleranceSamples)
 			return false;
 		float frequencyOffset = (float) frequencyOffsetMean(freqOffs);
-		int scanLineSamples = (int) Math.round(mean);
 		Mode mode = detectMode(modes, scanLineSamples);
 		boolean pictureChanged = lastMode != mode
 			|| Math.abs(lastScanLineSamples - scanLineSamples) > scanLineToleranceSamples
diff --git a/app/src/main/java/xdsopl/robot36/RGBDecoder.java b/app/src/main/java/xdsopl/robot36/RGBDecoder.java
index 056b361..de434f5 100644
--- a/app/src/main/java/xdsopl/robot36/RGBDecoder.java
+++ b/app/src/main/java/xdsopl/robot36/RGBDecoder.java
@@ -23,11 +23,11 @@ public class RGBDecoder implements Mode {
 		this.name = name;
 		scanLineSamples = (int) Math.round(scanLineSeconds * sampleRate);
 		beginSamples = (int) Math.round(beginSeconds * sampleRate);
-		redBeginSamples = (int) Math.round(redBeginSeconds * sampleRate);
+		redBeginSamples = (int) Math.round(redBeginSeconds * sampleRate) - beginSamples;
 		redSamples = (int) Math.round((redEndSeconds - redBeginSeconds) * sampleRate);
-		greenBeginSamples = (int) Math.round(greenBeginSeconds * sampleRate);
+		greenBeginSamples = (int) Math.round(greenBeginSeconds * sampleRate) - beginSamples;
 		greenSamples = (int) Math.round((greenEndSeconds - greenBeginSeconds) * sampleRate);
-		blueBeginSamples = (int) Math.round(blueBeginSeconds * sampleRate);
+		blueBeginSamples = (int) Math.round(blueBeginSeconds * sampleRate) - beginSamples;
 		blueSamples = (int) Math.round((blueEndSeconds - blueBeginSeconds) * sampleRate);
 		endSamples = (int) Math.round(endSeconds * sampleRate);
 		lowPassFilter = new ExponentialMovingAverage();
@@ -53,10 +53,10 @@ public class RGBDecoder implements Mode {
 			return 0;
 		lowPassFilter.cutoff(evenBuffer.length, 2 * greenSamples, 2);
 		lowPassFilter.reset();
-		for (int i = beginSamples; i < endSamples; ++i)
-			scratchBuffer[i] = lowPassFilter.avg(scanLineBuffer[syncPulseIndex + i]);
+		for (int i = 0; i < endSamples - beginSamples; ++i)
+			scratchBuffer[i] = lowPassFilter.avg(scanLineBuffer[syncPulseIndex + beginSamples + i]);
 		lowPassFilter.reset();
-		for (int i = endSamples - 1; i >= beginSamples; --i)
+		for (int i = endSamples - beginSamples - 1; i >= 0; --i)
 			scratchBuffer[i] = freqToLevel(lowPassFilter.avg(scratchBuffer[i]), frequencyOffset);
 		for (int i = 0; i < evenBuffer.length; ++i) {
 			int redPos = redBeginSamples + (i * redSamples) / evenBuffer.length;