diff --git a/Config.h b/Config.h
index 572f0e0..978f35f 100644
--- a/Config.h
+++ b/Config.h
@@ -37,8 +37,8 @@
 
 // Use a higher baudrate for host communication. Required for FM network !
 #define SERIAL_SPEED 115200 //suitable for most older boards (Arduino, Due STM32F1_POG etc). External FM will NOT work with this !
-// #define SERIAL_SPEED 230400 //Only works on newer board M4, M7, Teensy. External FM will works with this
-// #define SERIAL_SPEED 460800 // Experimantal
+// #define SERIAL_SPEED 230400 // Only works on newer board M4, M7, Teensy. External FM might work with this
+// #define SERIAL_SPEED 460800 // Only works on newer board M4, M7, Teensy. External FM should work with this
 
 // Allow the use of the COS line to lockout the modem
 // #define USE_COS_AS_LOCKOUT
diff --git a/FM.cpp b/FM.cpp
index d7ef530..4f6b93f 100644
--- a/FM.cpp
+++ b/FM.cpp
@@ -56,7 +56,7 @@ m_extEnabled(false),
 m_rxLevel(1),
 m_inputRFRB(2401U),   // 100ms of audio + 1 sample
 m_outputRFRB(2400U),  // 100ms of audio
-m_inputExtRB(2400U)   // 100ms of Audio
+m_inputExtRB()
 {
   m_statusTimer.setTimeout(1U, 0U);
 
@@ -727,8 +727,9 @@ uint8_t CFM::getSpace() const
 
 uint8_t CFM::writeData(const uint8_t* data, uint8_t length)
 {
+  //todo check if length is a multiple of 3
   m_inputExtRB.addData(data, length);
-  return 0U;//maybe return an error if overflowing ?
+  return 0U;
 }
 
 void CFM::insertDelay(uint16_t ms)
diff --git a/FMUpSampler.cpp b/FMUpSampler.cpp
index d0a0027..04fe705 100644
--- a/FMUpSampler.cpp
+++ b/FMUpSampler.cpp
@@ -21,69 +21,76 @@
 
 const uint32_t FM_UPSAMPLE_MASK = 0x00000FFFU;
 
-CFMUpSampler::CFMUpSampler(uint16_t length) :
+CFMUpSampler::CFMUpSampler() :
 m_upSampleIndex(0),
-m_pack({0U, 0U, 0U}),
-m_samples(length)
+m_pack(0U),
+m_packPointer(NULL),
+m_samples(3600U), //300ms of 12 bit 8kHz audio
+m_running(false)
 {
+  m_packPointer = (uint8_t*)&m_pack;
 }
 
 void CFMUpSampler::reset()
 {
     m_upSampleIndex = 0U;
-    m_pack = {0U, 0U, 0U};
+    m_pack = 0U;
     m_samples.reset();
+    m_running = false;
 }
 
 void CFMUpSampler::addData(const uint8_t* data, uint16_t length)
 {
-  for(uint16_t i = 0U; i < length; i++) {
-    switch (m_upSampleIndex)
-    {
-      case 0U:
-        m_pack.byte0 = data[i];
-      break;
-      case 1U:
-        m_pack.byte1 = data[i];
-      break;
-      case 2U: {
-        m_pack.byte2 = data[i];
-
-        uint32_t pack = 0U;
-        uint8_t* packPtr = (uint8_t*)&pack;
-
-        packPtr[0U] = m_pack.byte0;
-        packPtr[1U] = m_pack.byte1;
-        packPtr[2U] = m_pack.byte2;
-
-        q15_t sample2 = q15_t(uint16_t(pack & FM_UPSAMPLE_MASK) - 2048);
-        q15_t sample1 = q15_t(uint16_t(pack >> 12) - 2048);
-
-        m_samples.put(sample1);
-        m_samples.put(0);
-        m_samples.put(0);
-        m_samples.put(sample2);
-        m_samples.put(0);
-        m_samples.put(0);
-      }
-      break;
-      default:
-      //shoudl never happen
-      break;
-    }
-
-    m_upSampleIndex ++;
-    if (m_upSampleIndex > 2U)
-      m_upSampleIndex = 0U;
+  TSamplePairPack* packPointer = (TSamplePairPack*)data;
+  TSamplePairPack* packPointerEnd = packPointer + (length / 3U);
+  while(packPointer != packPointerEnd) {
+    m_samples.put(*packPointer);
+    packPointer++;
   }
+  if(!m_running)
+    m_running = m_samples.getData() > 300U;//75ms of audio
 }
 
 bool CFMUpSampler::getSample(q15_t& sample)
 {
-    return m_samples.get(sample);
+  if(!m_running)
+    return false;
+
+  switch (m_upSampleIndex)
+  {
+  case 0: {
+    TSamplePairPack pairPack;
+    if(!m_samples.get(pairPack)) {
+      m_running = false;
+      return false;
+    }
+      
+    m_pack = 0U;
+    m_packPointer = (uint8_t*)&m_pack;
+
+    m_packPointer[0U] = pairPack.byte0;
+    m_packPointer[1U] = pairPack.byte1;
+    m_packPointer[2U] = pairPack.byte2;
+
+    sample = q15_t(m_pack >> 12) - 2048;
+    break;
+  }
+  case 3:
+    sample = q15_t(m_pack & FM_UPSAMPLE_MASK) - 2048;
+  break;
+  default:
+    sample = 0;
+  break;
+  }
+
+  m_upSampleIndex++;
+  if(m_upSampleIndex >= 6U)
+    m_upSampleIndex = 0U;
+
+  return true;
 }
 
 uint16_t CFMUpSampler::getSpace() const
 {
-    return m_samples.getSpace();
+  return m_samples.getSpace();
 }
\ No newline at end of file
diff --git a/FMUpSampler.h b/FMUpSampler.h
index cee671b..b76982f 100644
--- a/FMUpSampler.h
+++ b/FMUpSampler.h
@@ -27,7 +27,7 @@
 
 class CFMUpSampler {
 public:
-  CFMUpSampler(uint16_t length);
+  CFMUpSampler();
 
   void reset();
 
@@ -39,8 +39,10 @@ public:
 
 private:
   uint8_t m_upSampleIndex;
-  TSamplePairPack m_pack;
-  CRingBuffer<q15_t> m_samples;
+  uint32_t m_pack;
+  uint8_t * m_packPointer;
+  CRingBuffer<TSamplePairPack> m_samples;
+  bool m_running;
 };
 
 #endif
\ No newline at end of file