Fix TII insertion for positive frequency carriers

3 files changed, 11 insertions, 15 deletions

diff --git a/doc/example.ini b/doc/example.ini
index d356ee1..ec0525c 100644
--- a/doc/example.ini
+++ b/doc/example.ini
@@ -318,8 +318,12 @@ offset=0.002
 ; DAB modes I and II are supported, and must be set explicitly in
 ; this file. Reading DAB mode from ETI is not supported.
 enable=0
-comb=16
-pattern=3
+; comb is also known as sub-identifier.
+comb=1
+; pattern is also known as main-identifier. If you run several transmitters
+; in SFN, it is better to use the same pattern for all, and vary the comb.
+; Otherwise identification of the transmitters may be more difficult.
+pattern=11
 ; There are two variants of TII being used. The old variant that uses the wrong
 ; phase on the second carrier in each carrier pairs and is therefore not
 ; conforming to the specification. Modern analysers can decode both variants,
diff --git a/src/TII.cpp b/src/TII.cpp
index af64c9f..446d9c6 100644
--- a/src/TII.cpp
+++ b/src/TII.cpp
@@ -197,10 +197,6 @@ int TII::process(Buffer* dataIn, Buffer* dataOut)
         complexf* in = reinterpret_cast<complexf*>(dataIn->getData());
         complexf* out = reinterpret_cast<complexf*>(dataOut->getData());
 
-        if ((m_enabled_carriers.size() % 2) != 0) {
-            throw std::logic_error("odd number of enabled carriers");
-        }
-
         /* Normalise the TII carrier power according to ETSI TR 101 496-3
          * Clause 5.4.2.2 Paragraph 7:
          *
@@ -213,13 +209,10 @@ int TII::process(Buffer* dataIn, Buffer* dataOut)
          */
         const float normalise_factor = 0.14433756729740644112f; // = 1/sqrt(48)
 
-        for (size_t i = 0; i < m_enabled_carriers.size(); i+=2) {
+        for (size_t i = 0; i < m_enabled_carriers.size(); i++) {
             // See header file for an explanation of the old variant
             if (m_enabled_carriers[i]) {
                 out[i] = normalise_factor * (m_conf.old_variant ? in[i+1] : in[i]);
-            }
-
-            if (m_enabled_carriers[i+1]) {
                 out[i+1] = normalise_factor * in[i+1];
             }
         }
@@ -239,10 +232,6 @@ void TII::enable_carrier(int k) {
     }
 
     m_enabled_carriers[ix] = true;
-    // NULL frequency is never enabled.
-    if (ix > 1 and (ix-1 != 768)) {
-        m_enabled_carriers[ix-1] = true;
-    }
 }
 
 void TII::prepare_pattern() {
@@ -287,7 +276,7 @@ void TII::prepare_pattern() {
             }
         }
 
-        for (int k = 384; k <= 768; k++) {
+        for (int k = 385; k <= 768; k++) {
             for (int b = 0; b < 8; b++) {
                 if (    k == 385 + 2 * comb + 48 * b and
                         pattern_tm1_2_4[m_conf.pattern][b]) {
diff --git a/src/TII.h b/src/TII.h
index fe67978..4c5c605 100644
--- a/src/TII.h
+++ b/src/TII.h
@@ -122,6 +122,9 @@ class TII : public ModCodec, public RemoteControllable
         // m_enabled_carriers is read by modulator thread, and written
         // to by RC thread.
         mutable boost::mutex m_enabled_carriers_mutex;
+
+        // m_enabled_carriers is true only for the first carrier in the
+        // active pair
         std::vector<bool> m_enabled_carriers;
 };