GNU Radio 3.5.1 C++ API
vocoder_cvsd_encode_sb.h
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00001 /* -*- c++ -*- */
00002 /*
00003  * Copyright 2007 Free Software Foundation, Inc.
00004  * 
00005  * This file is part of GNU Radio
00006  * 
00007  * GNU Radio is free software; you can redistribute it and/or modify
00008  * it under the terms of the GNU General Public License as published by
00009  * the Free Software Foundation; either version 3, or (at your option)
00010  * any later version.
00011  * 
00012  * GNU Radio is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015  * GNU General Public License for more details.
00016  * 
00017  * You should have received a copy of the GNU General Public License
00018  * along with GNU Radio; see the file COPYING.  If not, write to
00019  * the Free Software Foundation, Inc., 51 Franklin Street,
00020  * Boston, MA 02110-1301, USA.
00021  */
00022 #ifndef INCLUDED_VOCODER_CVSD_ENCODER_SB_H
00023 #define INCLUDED_VOCODER_CVSD_ENCODER_SB_H
00024 
00025 #include <vocoder_api.h>
00026 #include <gr_sync_decimator.h>
00027 
00028 class vocoder_cvsd_encode_sb;
00029 
00030 typedef boost::shared_ptr<vocoder_cvsd_encode_sb> vocoder_cvsd_encode_sb_sptr;
00031 
00032  /*!
00033   * \brief Constructor parameters to initialize the CVSD encoder.  The
00034   * default values are modeled after the Bluetooth standard and should
00035   * not be changed except by an advanced user
00036   *
00037   * \ingroup vocoder_blk
00038   *
00039   * \param min_step       Minimum step size used to update the internal reference.  Default: "10"
00040   * \param max_step       Maximum step size used to update the internal reference.  Default: "1280"
00041   * \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)
00042   * \param accum_decay    Decay factor applied to the internal reference during every interation of the codec.  Default: "0.96875"  (i.e. 1-1/32)
00043   * \param K;             Size of shift register; the number of output bits remembered by codec (must be less or equal to 32).  Default: "32"
00044   * \param J;             Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
00045   * \param pos_accum_max  Maximum integer value allowed for the internal reference.  Default: "32767" (2^15 - 1 or MAXSHORT)
00046   * \param neg_accum_max  Minimum integer value allowed for the internal reference.  Default: "-32767" (-2^15 + 1 or MINSHORT+1)
00047   *
00048   */
00049 
00050 VOCODER_API vocoder_cvsd_encode_sb_sptr vocoder_make_cvsd_encode_sb(short min_step=10,
00051                                                         short max_step=1280,
00052                                                         double step_decay=0.9990234375,
00053                                                         double accum_decay= 0.96875,
00054                                                         int K=32,
00055                                                         int J=4,
00056                                                         short pos_accum_max=32767,
00057                                                         short neg_accum_max=-32767);
00058 
00059 /*!
00060  * \brief This block performs CVSD audio encoding.  Its design and implementation
00061  * is modeled after the CVSD encoder/decoder specifications defined in the
00062  * Bluetooth standard.
00063  *
00064  * \ingroup vocoder_blk
00065  *
00066  * CVSD is a method for encoding speech that seeks to reduce the
00067  * bandwidth required for digital voice transmission.  CVSD takes
00068  * advantage of strong correlation between samples, quantizing the
00069  * difference in amplitude between two consecutive samples.  This
00070  * difference requires fewer quantization levels as compared to other
00071  * methods that quantize the actual amplitude level, reducing the
00072  * bandwidth.  CVSD employs a two level quantizer (one bit) and an
00073  * adaptive algorithm that allows for continuous step size adjustment.
00074  *
00075  * The coder can represent low amplitude signals with accuracy without
00076  * sacrificing performance on large amplitude signals, a trade off that
00077  * occurs in some non-adaptive modulations.
00078  *
00079  * The CVSD encoder effectively provides 8-to-1 compression.  More
00080  * specifically, each incoming audio sample is compared to an internal
00081  * reference value.  If the input is greater or equal to the reference,
00082  * the encoder outputs a "1" bit.  If the input is less than the reference,
00083  * the encoder outputs a "0" bit.  The reference value is then updated
00084  * accordingly based on the frequency of outputted "1" or "0" bits.  By
00085  * grouping 8 outputs bits together, the encoder essentially produce one
00086  * output byte for every 8 input audio samples.
00087  *
00088  * This encoder requires that input audio samples are 2-byte short signed
00089  * integers.  The result bandwidth conversion, therefore, is 16 input bytes
00090  * of raw audio data to 1 output byte of encoded audio data.
00091  *
00092  * The CVSD encoder module must be prefixed by an up-converter to over-sample
00093  * the audio data prior to encoding.  The Bluetooth standard specifically
00094  * calls for a 1-to-8 interpolating up-converter.  While this reduces the
00095  * overall compression of the codec, this is required so that the encoder
00096  * can accurately compute the slope between adjacent audio samples and
00097  * correctly update its internal reference value.
00098  *
00099  * References:
00100  *
00101  * 1.  Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
00102  *     Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
00103  *
00104  * 2.  Specification of The Bluetooth System
00105  *     Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
00106  *
00107  * 3.  McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
00108  *     Bluetooth Voice Simulink® Model, Available:
00109  *     http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
00110  *
00111  */
00112 
00113 class VOCODER_API vocoder_cvsd_encode_sb : public gr_sync_decimator
00114 {
00115 private:
00116   friend VOCODER_API vocoder_cvsd_encode_sb_sptr vocoder_make_cvsd_encode_sb(short min_step,
00117                                                                  short max_step,
00118                                                                  double step_decay,
00119                                                                  double accum_decay,
00120                                                                  int K,
00121                                                                  int J,
00122                                                                  short pos_accum_max,
00123                                                                  short neg_accum_max);
00124 
00125   vocoder_cvsd_encode_sb(short min_step, short max_step, double step_decay,
00126                          double accum_decay, int K, int J,
00127                          short pos_accum_max, short neg_accum_max);
00128   
00129   //! Member functions required by the encoder/decoder
00130   //! \brief Rounding function specific to CVSD
00131   //! \return the input value rounded to the nearest integer
00132   int cvsd_round(double input);
00133   
00134   //! \brief A power function specific to CVSD data formats
00135   //! \return (radix)^power, where radix and power are short integers
00136   unsigned int cvsd_pow (short radix, short power);
00137  
00138   //! \brief Sums number of 1's in the input
00139   //! \return the number of 1s in the four bytes of an input unsigned integer
00140   unsigned char cvsd_bitwise_sum (unsigned int input);
00141 
00142   // Members variables related to the CVSD encoder use to update interal reference value
00143   short d_min_step;
00144   short d_max_step;
00145   double d_step_decay;
00146   double d_accum_decay;
00147 
00148   int d_K; //!< \brief Size of shift register; the number of output bits remembered in shift register
00149   int d_J; //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
00150   
00151   short d_pos_accum_max;
00152   short d_neg_accum_max;
00153 
00154   int d_accum;            //!< \brief Current value of internal reference
00155   int d_loop_counter;     //!< \brief Current value of the loop counter
00156   unsigned int d_runner;  //!< \brief Current value of the shift register
00157   short d_stepsize;       //!< \brief Current value of the step sizer
00158 
00159  public:
00160   ~vocoder_cvsd_encode_sb ();   // public destructor
00161 
00162   short min_step() { return d_min_step; }
00163   short max_step() { return d_max_step; }
00164   double step_decay() { return d_step_decay; }
00165   double accum_decay() { return d_accum_decay; }
00166   int K() { return d_K; }
00167   int J() { return d_J; }
00168   short pos_accum_max() { return d_pos_accum_max; }
00169   short neg_accum_max() { return d_neg_accum_max; }
00170 
00171   int work (int noutput_items,
00172             gr_vector_const_void_star &input_items,
00173             gr_vector_void_star &output_items);
00174 };
00175 
00176 #endif /* INCLUDED_VOCODER_CVSD_ENCODE_SB_H */