Revert "Normalise TII to 1/sqrt(48)" and fix TII level in GainControl

This reverts commit c7961c2e8688d6db2a87b5079c60a04b8fe37e74.

3 files changed, 21 insertions, 12 deletions

diff --git a/src/GainControl.cpp b/src/GainControl.cpp
index c111de3..d90da45 100644
--- a/src/GainControl.cpp
+++ b/src/GainControl.cpp
@@ -127,21 +127,25 @@ int GainControl::internal_process(Buffer* const dataIn, Buffer* dataOut)
 
     if ((sizeIn % m_frameSize) != 0) {
         PDEBUG("%zu != %zu\n", sizeIn, m_frameSize);
-        throw std::runtime_error(
-                "GainControl::process input size not valid!");
+        throw std::runtime_error("GainControl::process input size not valid!");
     }
 
     const auto constantGain4 = _mm_set1_ps(constantGain);
 
     for (size_t i = 0; i < sizeIn; i += m_frameSize) {
-        gain128.m = computeGain(in, m_frameSize);
+        // Do not apply gain computation to the NULL symbol, which either
+        // is blank or contains TII. Apply the gain calculation from the next
+        // symbol on the NULL symbol to get consistent TII power.
+        if (i > 0) {
+            gain128.m = computeGain(in, m_frameSize);
+        }
+        else {
+            gain128.m = computeGain(in + m_frameSize, m_frameSize);
+        }
         gain128.m = _mm_mul_ps(gain128.m, constantGain4);
 
         PDEBUG("********** Gain: %10f **********\n", gain128.f[0]);
 
-        ////////////////////////////////////////////////////////////////////////
-        // Applying gain to output data
-        ////////////////////////////////////////////////////////////////////////
         for (size_t sample = 0; sample < m_frameSize; ++sample) {
             out[sample] = _mm_mul_ps(in[sample], gain128.m);
         }
@@ -163,7 +167,12 @@ int GainControl::internal_process(Buffer* const dataIn, Buffer* dataOut)
     }
 
     for (size_t i = 0; i < sizeIn; i += m_frameSize) {
-        gain = constantGain * computeGain(in, m_frameSize);
+        // Do not apply gain computation to the NULL symbol, which either
+        // is blank or contains TII. Apply the gain calculation from the next
+        // symbol on the NULL symbol to get consistent TII power.
+        gain = constantGain * (i > 0 ?
+                computeGain(in, m_frameSize) :
+                computeGain(in + m_frameSize, m_frameSize));
 
         PDEBUG("********** Gain: %10f **********\n", gain);
 
diff --git a/src/GainControl.h b/src/GainControl.h
index f0fd6b6..f024fa2 100644
--- a/src/GainControl.h
+++ b/src/GainControl.h
@@ -38,6 +38,7 @@
 #include <complex>
 #include <string>
 #include <mutex>
+
 #ifdef __SSE__
 #   include <xmmintrin.h>
 #endif
diff --git a/src/TII.cpp b/src/TII.cpp
index 2d7429f..b329cdb 100644
--- a/src/TII.cpp
+++ b/src/TII.cpp
@@ -189,8 +189,6 @@ int TII::process(Buffer* dataIn, Buffer* dataOut)
         complexf* in = reinterpret_cast<complexf*>(dataIn->getData());
         complexf* out = reinterpret_cast<complexf*>(dataOut->getData());
 
-        constexpr float normalisation = 0.144337f; // 1/sqrt(48);
-
         /* Normalise the TII carrier power according to ETSI TR 101 496-3
          * Clause 5.4.2.2 Paragraph 7:
          *
@@ -198,7 +196,8 @@ int TII::process(Buffer* dataIn, Buffer* dataOut)
          * > is 1:48 for all Modes, so that the signal power in a TII symbol is
          * > 16 dB below the signal power of the other symbols.
          *
-         * Divide by sqrt(48) because I and Q are separately normalised.
+         * This is because we only enable 32 out of 1536 carriers, not because
+         * every carrier is lower power.
          */
         for (size_t i = 0; i < m_Acp.size(); i++) {
             /* See header file for an explanation of the old variant.
@@ -219,8 +218,8 @@ int TII::process(Buffer* dataIn, Buffer* dataOut)
              * and fuse the two conditionals together:
              */
             if (m_Acp[i]) {
-                out[i] = in[i] * normalisation;
-                out[i+1] = (m_conf.old_variant ? in[i+1] : in[i]) * normalisation;
+                out[i] = in[i];
+                out[i+1] = (m_conf.old_variant ? in[i+1] : in[i]);
             }
         }
     }