diff --git a/src/ggwave.cpp b/src/ggwave.cpp
index ecbf396..e4fc339 100644
--- a/src/ggwave.cpp
+++ b/src/ggwave.cpp
@@ -700,34 +700,6 @@ bool GGWave::encode(const CBWaveformOut & cbWaveformOut) {
         m_resampler->reset();
     }
 
-    for (int k = 0; k < (int) m_tx->phaseOffsets.size(); ++k) {
-        m_tx->phaseOffsets[k] = (M_PI*k)/(m_tx->txProtocol.nDataBitsPerTx());
-    }
-
-    // note : what is the purpose of this shuffle ? I forgot .. :(
-    //std::random_device rd;
-    //std::mt19937 g(rd());
-
-    //std::shuffle(phaseOffsets.begin(), phaseOffsets.end(), g);
-
-    for (int k = 0; k < (int) m_tx->dataBits.size(); ++k) {
-        const double freq = bitFreq(m_tx->txProtocol, k);
-
-        const double phaseOffset = m_tx->phaseOffsets[k];
-        const double curHzPerSample = m_hzPerSample;
-        const double curIHzPerSample = 1.0/curHzPerSample;
-
-        for (int i = 0; i < m_samplesPerFrame; i++) {
-            const double curi = i;
-            m_tx->bit1Amplitude[k][i] = std::sin((2.0*M_PI)*(curi*m_isamplesPerFrame)*(freq*curIHzPerSample) + phaseOffset);
-        }
-
-        for (int i = 0; i < m_samplesPerFrame; i++) {
-            const double curi = i;
-            m_tx->bit0Amplitude[k][i] = std::sin((2.0*M_PI)*(curi*m_isamplesPerFrame)*((freq + m_hzPerSample*m_freqDelta_bin)*curIHzPerSample) + phaseOffset);
-        }
-    }
-
     const int nECCBytesPerTx = getECCBytesForLength(m_tx->txDataLength);
     const int sendDataLength = m_tx->txDataLength + m_encodedDataOffset;
     const int totalBytes = sendDataLength + nECCBytesPerTx;
@@ -813,6 +785,37 @@ bool GGWave::encode(const CBWaveformOut & cbWaveformOut) {
         }
     }
 
+    // compute Tx data
+    {
+        for (int k = 0; k < (int) m_tx->phaseOffsets.size(); ++k) {
+            m_tx->phaseOffsets[k] = (M_PI*k)/(m_tx->txProtocol.nDataBitsPerTx());
+        }
+
+        // note : what is the purpose of this shuffle ? I forgot .. :(
+        //std::random_device rd;
+        //std::mt19937 g(rd());
+
+        //std::shuffle(phaseOffsets.begin(), phaseOffsets.end(), g);
+
+        for (int k = 0; k < (int) m_tx->dataBits.size(); ++k) {
+            const double freq = bitFreq(m_tx->txProtocol, k);
+
+            const double phaseOffset = m_tx->phaseOffsets[k];
+            const double curHzPerSample = m_hzPerSample;
+            const double curIHzPerSample = 1.0/curHzPerSample;
+
+            for (int i = 0; i < m_samplesPerFrame; i++) {
+                const double curi = i;
+                m_tx->bit1Amplitude[k][i] = std::sin((2.0*M_PI)*(curi*m_isamplesPerFrame)*(freq*curIHzPerSample) + phaseOffset);
+            }
+
+            for (int i = 0; i < m_samplesPerFrame; i++) {
+                const double curi = i;
+                m_tx->bit0Amplitude[k][i] = std::sin((2.0*M_PI)*(curi*m_isamplesPerFrame)*((freq + m_hzPerSample*m_freqDelta_bin)*curIHzPerSample) + phaseOffset);
+            }
+        }
+    }
+
     int frameId = 0;
     uint32_t offset = 0;
     const float factor = m_sampleRate/m_sampleRateOut;