adding proper documentation to CVSD vocoder

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@5096 221aa14e-8319-0410-a670-987f0aec2ac5

1 files changed, 87 insertions, 10 deletions

diff --git a/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h b/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h
index 57734ca15..066a477f4 100644
--- a/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h
+++ b/gr-cvsd-vocoder/src/lib/cvsd_encode_sb.h
@@ -28,6 +28,22 @@ class cvsd_encode_sb;
 
 typedef boost::shared_ptr<cvsd_encode_sb> cvsd_encode_sb_sptr;
 
+ /*!
+  * \brief Constructor parameters to initialize the CVSD encoder.  The default
+  * values are modeled after the Bluetooth standard and should not be changed
+  * except by an advanced user
+  *
+  * \param min_step       Minimum step size used to update the internal reference.  Default: "10"
+  * \param max_step       Maximum step size used to update the internal reference.  Default: "1280"
+  * \param step_decay     Decay factor applied to step size when there is not a run of J output 1s or 0s.  Default: "0.9990234375"  (i.e. 1-1/1024)
+  * \param accum_decay    Decay factor applied to the internal reference during every interation of the codec.  Default: "0.96875"  (i.e. 1-1/32)
+  * \param K;             Size of shift register; the number of output bits remembered by codec (must be less or equal to 32).  Default: "32"
+  * \param J;             Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
+  * \param pos_accum_max  Maximum integer value allowed for the internal reference.  Default: "32767" (2^15 - 1 or MAXSHORT)
+  * \param neg_accum_max  Minimum integer value allowed for the internal reference.  Default: "-32767" (-2^15 + 1 or MINSHORT+1)
+  *
+  */
+
 cvsd_encode_sb_sptr cvsd_make_encode_sb (short min_step=10,
 					 short max_step=1280,
 					 double step_decay=0.9990234375,
@@ -37,6 +53,60 @@ cvsd_encode_sb_sptr cvsd_make_encode_sb (short min_step=10,
 					 short pos_accum_max=32767,
 					 short neg_accum_max=-32767);
 
+/*!
+ * \brief This block performs CVSD audio encoding.  Its design and implementation
+ * is modeled after the CVSD encoder/decoder specifications defined in the
+ * Bluetooth standard.
+ *
+ * \ingroup block
+ *
+ * CVSD is a method for encoding speech that seeks to reduce the
+ * bandwidth required for digital voice transmission.  CVSD takes
+ * advantage of strong correlation between samples, quantizing the
+ * difference in amplitude between two consecutive samples.  This
+ * difference requires fewer quantization levels as compared to other
+ * methods that quantize the actual amplitude level, reducing the
+ * bandwidth.  CVSD employs a two level quantizer (one bit) and an
+ * adaptive algorithm that allows for continuous step size adjustment.
+ *
+ * The coder can represent low amplitude signals with accuracy without
+ * sacrificing performance on large amplitude signals, a trade off that
+ * occurs in some non-adaptive modulations.
+ *
+ * The CVSD encoder effectively provides 8-to-1 compression.  More
+ * specifically, each incoming audio sample is compared to an internal
+ * reference value.  If the input is greater or equal to the reference,
+ * the encoder outputs a "1" bit.  If the input is less than the reference,
+ * the encoder outputs a "0" bit.  The reference value is then updated
+ * accordingly based on the frequency of outputted "1" or "0" bits.  By
+ * grouping 8 outputs bits together, the encoder essentially produce one
+ * output byte for every 8 input audio samples.
+ *
+ * This encoder requires that input audio samples are 2-byte short signed
+ * integers.  The result bandwidth conversion, therefore, is 16 input bytes
+ * of raw audio data to 1 output byte of encoded audio data.
+ *
+ * The CVSD encoder module must be prefixed by an up-converter to over-sample
+ * the audio data prior to encoding.  The Bluetooth standard specifically
+ * calls for a 1-to-8 interpolating up-converter.  While this reduces the
+ * overall compression of the codec, this is required so that the encoder
+ * can accurately compute the slope between adjacent audio samples and
+ * correctly update its internal reference value.
+ *
+ * References:
+ *
+ * 1.  Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
+ *     Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
+ *
+ * 2.  Specification of The Bluetooth System
+ *     Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
+ *
+ * 3.  McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
+ *     Bluetooth Voice Simulink® Model, Available:
+ *     http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
+ *
+ */
+
 class cvsd_encode_sb : public gr_sync_decimator
 {
 private:
@@ -53,28 +123,35 @@ private:
 		  double accum_decay, int K, int J,
 		  short pos_accum_max, short neg_accum_max);
   
+  //! Member functions required by the encoder/decoder
+  //! \brief Rounding function specific to CVSD
+  //! \return the input value rounded to the nearest integer
   int cvsd_round(double input);
+  
+  //! \brief A power function specific to CVSD data formats
+  //! \return (radix)^power, where radix and power are short integers
   unsigned int cvsd_pow (short radix, short power);
+ 
+  //! \brief Sums number of 1's in the input
+  //! \return the number of 1s in the four bytes of an input unsigned integer
   unsigned char cvsd_bitwise_sum (unsigned int input);
 
+  // Members variables related to the CVSD encoder use to update interal reference value
   short d_min_step;
   short d_max_step;
   double d_step_decay;
   double d_accum_decay;
 
-  //! \brief Size of shift register; the number of output bits remembered in shift register
-  int d_K;
-
-  //! \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
-  int d_J;
-
+  int d_K; //!< \brief Size of shift register; the number of output bits remembered in shift register
+  int d_J; //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
+  
   short d_pos_accum_max;
   short d_neg_accum_max;
 
-  int d_accum;
-  int d_loop_counter;
-  unsigned int d_runner;
-  short d_stepsize;
+  int d_accum;            //!< \brief Current value of internal reference
+  int d_loop_counter;     //!< \brief Current value of the loop counter
+  unsigned int d_runner;  //!< \brief Current value of the shift register
+  short d_stepsize;       //!< \brief Current value of the step sizer
 
  public:
   ~cvsd_encode_sb ();	// public destructor