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.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