GNU Radio 3.5.1 C++ API
vocoder_cvsd_decode_bs.h
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00001 /* -*- c++ -*- */
00002 /*
00003  * Copyright 2007,2011 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 
00023 #ifndef INCLUDED_VOCODER_CVSD_DECODE_BS_H
00024 #define INCLUDED_VOCODER_CVSD_DECODE_BS_H
00025 
00026 #include <vocoder_api.h>
00027 #include <gr_sync_interpolator.h>
00028 
00029 class vocoder_cvsd_decode_bs;
00030 
00031 typedef boost::shared_ptr<vocoder_cvsd_decode_bs> vocoder_cvsd_decode_bs_sptr;
00032 
00033  /*!
00034   * \brief Constructor parameters to initialize the CVSD decoder.  The default
00035   * values are modeled after the Bluetooth standard and should not be changed,
00036   * except by an advanced user
00037   *
00038   * \ingroup vocoder_blk
00039   *
00040   * \param min_step       Minimum step size used to update the internal reference.  Default: "10"
00041   * \param max_step       Maximum step size used to update the internal reference.  Default: "1280"
00042   * \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)
00043   * \param accum_decay    Decay factor applied to the internal reference during every interation of the codec.  Default: "0.96875"  (i.e. 1-1/32)
00044   * \param K;             Size of shift register; the number of output bits remembered by codec (must be less or equal to 32).  Default: "32"
00045   * \param J;             Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
00046   * \param pos_accum_max  Maximum integer value allowed for the internal reference.  Default: "32767" (2^15 - 1 or MAXSHORT)
00047   * \param neg_accum_max  Minimum integer value allowed for the internal reference.  Default: "-32767" (-2^15 + 1 or MINSHORT+1)
00048   *
00049   */
00050 VOCODER_API vocoder_cvsd_decode_bs_sptr vocoder_make_cvsd_decode_bs (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 decoding.  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 decoder effectively provides 1-to-8 decompression.  More
00080  * specifically, for each incoming input bit, the decoder outputs one
00081  * audio sample.  If the input is a "1" bit, the internal reference is
00082  * increased appropriately and then outputted as the next estimated audio
00083  * sample.  If the input is a "0" bit, the internal reference is
00084  * decreased appropriately and then likewise outputted as the next estimated
00085  * audio sample.  Grouping 8 input bits together, the encoder essentially
00086  * produces 8 output audio samples for everyone one input byte.
00087  *
00088  * This decoder requires that output audio samples are 2-byte short signed
00089  * integers.  The result bandwidth conversion, therefore, is 1 byte of
00090  * encoded audio data to 16 output bytes of raw audio data.
00091  *
00092  * The CVSD decoder module must be post-fixed by a down-converter to
00093  * under-sample the audio data after decoding.  The Bluetooth standard
00094  * specifically calls for a 8-to-1 decimating down-converter.  This is
00095  * required so that so that output sampling rate equals the original input
00096  * sampling rate present before the encoder.  In all cases, the output
00097  * down-converter rate must be the inverse of the input up-converter rate
00098  * before the CVSD encoder.
00099  *
00100  * References:
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  * 2.  Specification of The Bluetooth System
00104  *         Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
00105  * 3.  McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
00106  *         Bluetooth Voice Simulink® Model, Available:
00107  *         http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
00108  *
00109  */
00110 
00111 class VOCODER_API vocoder_cvsd_decode_bs : public gr_sync_interpolator
00112 {
00113 private:
00114   friend VOCODER_API vocoder_cvsd_decode_bs_sptr vocoder_make_cvsd_decode_bs (short min_step,
00115                                                                   short max_step,
00116                                                                   double step_decay,
00117                                                                   double accum_decay,
00118                                                                   int K,
00119                                                                   int J,
00120                                                                   short pos_accum_max,
00121                                                                   short neg_accum_max);
00122 
00123   vocoder_cvsd_decode_bs (short min_step, short max_step, double step_decay,
00124                           double accum_decay, int K, int J,
00125                           short pos_accum_max, short neg_accum_max);
00126 
00127   //! Member functions required by the encoder/decoder
00128   //! \brief Rounding function specific to CVSD
00129   //! \return the input value rounded to the nearest integer
00130   int cvsd_round(double input);
00131   
00132   //! \brief A power function specific to CVSD data formats
00133   //! \return (radix)^power, where radix and power are short integers
00134   unsigned int cvsd_pow (short radix, short power);
00135  
00136   //! \brief Sums number of 1's in the input
00137   //! \return the number of 1s in the four bytes of an input unsigned integer
00138   unsigned char cvsd_bitwise_sum (unsigned int input);
00139 
00140   short d_min_step;
00141   short d_max_step;
00142   double d_step_decay;
00143   double d_accum_decay;
00144 
00145   int d_K;  //!< \brief Size of shift register; the number of output bits remembered in shift register
00146   int d_J;  //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
00147 
00148   short d_pos_accum_max;
00149   short d_neg_accum_max;
00150 
00151   int d_accum;                //!< \brief Current value of internal reference
00152   int d_loop_counter;         //!< \brief Current value of the loop counter
00153   unsigned int d_runner;      //!< \brief Current value of the shift register
00154   unsigned int d_runner_mask; //!< \brief Value of the mask to access the last J bits of the shift register
00155   short d_stepsize;           //!< \brief Current value of the step sizer
00156 
00157  public:
00158   ~vocoder_cvsd_decode_bs ();   // public destructor
00159 
00160   short min_step() { return d_min_step; }
00161   short max_step() { return d_max_step; }
00162   double step_decay() { return d_step_decay; }
00163   double accum_decay() { return d_accum_decay; }
00164   int K() { return d_K; }
00165   int J() { return d_J; }
00166   short pos_accum_max() { return d_pos_accum_max; }
00167   short neg_accum_max() { return d_neg_accum_max; }
00168 
00169   int work (int noutput_items,
00170             gr_vector_const_void_star &input_items,
00171             gr_vector_void_star &output_items);
00172 };
00173 
00174 #endif /* INCLUDED_VOCODER_CVSD_DECODE_BS_H */