GNU Radio 3.5.3.2 C++ API
|
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 */