diff --git a/plugins/samplesource/rtlsdr/rtlsdrthread.cpp b/plugins/samplesource/rtlsdr/rtlsdrthread.cpp
index 6c1ee8a17..46ec77e11 100644
--- a/plugins/samplesource/rtlsdr/rtlsdrthread.cpp
+++ b/plugins/samplesource/rtlsdr/rtlsdrthread.cpp
@@ -88,7 +88,7 @@ void RTLSDRThread::run()
 }
 
 //  Decimate according to specified log2 (ex: log2=4 => decim=16)
-void RTLSDRThread::callback(const quint8* buf, qint32 len)
+void RTLSDRThread::callback(const qint8* buf, qint32 len)
 {
 	SampleVector::iterator it = m_convertBuffer.begin();
 
@@ -178,6 +178,9 @@ void RTLSDRThread::callback(const quint8* buf, qint32 len)
 void RTLSDRThread::callbackHelper(unsigned char* buf, uint32_t len, void* ctx)
 {
 	RTLSDRThread* thread = (RTLSDRThread*)ctx;
-	thread->callback(buf, len);
+	for (unsigned int i = 0; i < len; i++) {
+	    buf[i] = buf[i] - 127;
+	}
+	thread->callback((qint8 *) buf, len);
 }
 
diff --git a/plugins/samplesource/rtlsdr/rtlsdrthread.h b/plugins/samplesource/rtlsdr/rtlsdrthread.h
index b5b35e080..8a9debf5f 100644
--- a/plugins/samplesource/rtlsdr/rtlsdrthread.h
+++ b/plugins/samplesource/rtlsdr/rtlsdrthread.h
@@ -52,10 +52,10 @@ private:
 	unsigned int m_log2Decim;
 	int m_fcPos;
 
-	Decimators<quint8, SDR_SAMP_SZ, 8> m_decimators;
+	Decimators<qint8, SDR_SAMP_SZ, 8> m_decimators;
 
 	void run();
-	void callback(const quint8* buf, qint32 len);
+	void callback(const qint8* buf, qint32 len);
 
 	static void callbackHelper(unsigned char* buf, uint32_t len, void* ctx);
 };
diff --git a/sdrbase/dsp/decimators.h b/sdrbase/dsp/decimators.h
index ef5b64566..c4645c2da 100644
--- a/sdrbase/dsp/decimators.h
+++ b/sdrbase/dsp/decimators.h
@@ -83,18 +83,18 @@ struct decimation_shifts<16, 12>
 template<>
 struct decimation_shifts<16, 8>
 {
-    static const uint pre1   = 7;
-    static const uint pre2   = 6;
+    static const uint pre1   = 8;
+    static const uint pre2   = 7;
     static const uint post2  = 0;
-    static const uint pre4   = 5;
+    static const uint pre4   = 6;
     static const uint post4  = 0;
-    static const uint pre8   = 4;
+    static const uint pre8   = 5;
     static const uint post8  = 0;
-    static const uint pre16  = 3;
+    static const uint pre16  = 4;
     static const uint post16 = 0;
-    static const uint pre32  = 2;
+    static const uint pre32  = 3;
     static const uint post32 = 0;
-    static const uint pre64  = 1;
+    static const uint pre64  = 2;
     static const uint post64 = 0;
 };