refs #144 , improved SELCAL in a way that SELCAL tones will always end with 0 amplitude.

* method to write values in buffer -> writeAmplitudeToBuffer
* fixes the range from the last 0 pass so SELCAL tones will always end with 0 amplitude

src/blacksound/soundgenerator.cpp

@@ -157,14 +157,14 @@ namespace BlackSound
         foreach(Tone t, this->m_tones)
         {
             qint64 bytesPerTone = this->m_audioFormat.sampleRate() * bytesForAllChannels * t.m_durationMs / 1000;
+            qint64 last0AmplitudeSample = bytesPerTone; // last sample when amplitude was 0
             int sampleIndexPerTone = 0;
-
             while (bytesPerTone)
             {
                 // http://hyperphysics.phy-astr.gsu.edu/hbase/audio/sumdif.html
                 // http://math.stackexchange.com/questions/164369/how-do-you-calculate-the-frequency-perceived-by-humans-of-two-sinusoidal-waves-a
                 const double pseudoTime = double(sampleIndexPerTone % this->m_audioFormat.sampleRate()) / this->m_audioFormat.sampleRate();
-                double amplitude = 0; // silence
+                double amplitude = 0.0; // amplitude -1 -> +1 , 0 is silence
                 if (t.m_frequencyHz > 10)
                 {
                     // the combination of two frequencies actually would have 2*amplitude,
@@ -176,7 +176,49 @@ namespace BlackSound
                                 qCos(M_PI * (t.m_frequencyHz - t.m_secondaryFrequencyHz) * pseudoTime);
                 }
 
+                // avoid overflow
+                Q_ASSERT(amplitude <= 1.0 && amplitude >= -1.0);
+                if (amplitude < -1.0)
+                    amplitude = -1.0;
+                else if (amplitude > 1.0)
+                    amplitude = 1.0;
+                else if (qAbs(amplitude) < double(1.0 / 65535))
+                {
+                    amplitude = 0;
+                    last0AmplitudeSample = bytesPerTone;
+                }
+
+                // generate this for all channels, usually 1 channel
                 for (int i = 0; i < this->m_audioFormat.channelCount(); ++i)
+                {
+                    this->writeAmplitudeToBuffer(amplitude, bufferPointer);
+                    bufferPointer += bytesPerSample;
+                    bytesPerTone -= bytesPerSample;
+                }
+                ++sampleIndexPerTone;
+            }
+
+            // fixes the range from the last 0 pass through
+            if (last0AmplitudeSample > 0)
+            {
+                bufferPointer -= last0AmplitudeSample;
+                while (last0AmplitudeSample)
+                {
+                    double amplitude = 0.0; // amplitude -1 -> +1 , 0 is silence
+
+                    // generate this for all channels, usually 1 channel
+                    for (int i = 0; i < this->m_audioFormat.channelCount(); ++i)
+                    {
+                        this->writeAmplitudeToBuffer(amplitude, bufferPointer);
+                        bufferPointer += bytesPerSample;
+                        last0AmplitudeSample -= bytesPerSample;
+                    }
+                }
+            }
+        }
+    }
+
+    void CSoundGenerator::writeAmplitudeToBuffer(const double amplitude, unsigned char *bufferPointer)
     {
         if (this->m_audioFormat.sampleSize() == 8 && this->m_audioFormat.sampleType() == QAudioFormat::UnSignedInt)
         {
@@ -204,13 +246,6 @@ namespace BlackSound
             else
                 qToBigEndian<qint16>(value, bufferPointer);
         }
-
-                    bufferPointer += bytesPerSample;
-                    bytesPerTone -= bytesPerSample;
-                }
-                ++sampleIndexPerTone;
-            }
-        }
     }
 
     bool CSoundGenerator::saveToWavFile(const QString &fileName) const
@@ -450,7 +485,6 @@ namespace BlackSound
     void CSoundGenerator::playFile(qint32 volume, const QString &file, bool removeFileAfterPlaying)
     {
         if (!QFile::exists(file)) return;
-
         QMediaPlayer *mediaPlayer = CSoundGenerator::mediaPlayer();
         QMediaResource mediaResource(QUrl(file), "audio");
         QMediaContent media(mediaResource);

src/blacksound/soundgenerator.h

@@ -344,6 +344,12 @@ namespace BlackSound
         //! \brief save buffer to wav file
         bool saveToWavFile(const QString &fileName) const;
 
+        /*!
+         * \brief Write amplitude to buffer
+         * \param amplitude value -1 .. 1
+         * \param bufferPointer current buffer pointer
+         */
+        void writeAmplitudeToBuffer(const double amplitude, unsigned char *bufferPointer);
     };
 } //namespace