GNU Radio 3.7.1 C++ API
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00001 /* -*- c++ -*- */ 00002 /* 00003 * Copyright 2007,2013 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 <gnuradio/vocoder/api.h> 00026 #include <gnuradio/sync_decimator.h> 00027 00028 namespace gr { 00029 namespace vocoder { 00030 00031 /*! 00032 * \brief This block performs CVSD audio encoding. Its design and 00033 * implementation is modeled after the CVSD encoder/decoder 00034 * specifications defined in the Bluetooth standard. 00035 * \ingroup audio_blk 00036 * 00037 * \details 00038 * CVSD is a method for encoding speech that seeks to reduce the 00039 * bandwidth required for digital voice transmission. CVSD takes 00040 * advantage of strong correlation between samples, quantizing the 00041 * difference in amplitude between two consecutive samples. This 00042 * difference requires fewer quantization levels as compared to 00043 * other methods that quantize the actual amplitude level, 00044 * reducing the bandwidth. CVSD employs a two level quantizer 00045 * (one bit) and an adaptive algorithm that allows for continuous 00046 * step size adjustment. 00047 * 00048 * The coder can represent low amplitude signals with accuracy 00049 * without sacrificing performance on large amplitude signals, a 00050 * trade off that occurs in some non-adaptive modulations. 00051 * 00052 * The CVSD encoder effectively provides 8-to-1 compression. More 00053 * specifically, each incoming audio sample is compared to an 00054 * internal reference value. If the input is greater or equal to 00055 * the reference, the encoder outputs a "1" bit. If the input is 00056 * less than the reference, the encoder outputs a "0" bit. The 00057 * reference value is then updated accordingly based on the 00058 * frequency of outputted "1" or "0" bits. By grouping 8 outputs 00059 * bits together, the encoder essentially produce one output byte 00060 * for every 8 input audio samples. 00061 * 00062 * This encoder requires that input audio samples are 2-byte short 00063 * signed integers. The result bandwidth conversion, therefore, 00064 * is 16 input bytes of raw audio data to 1 output byte of encoded 00065 * audio data. 00066 * 00067 * The CVSD encoder module must be prefixed by an up-converter to 00068 * over-sample the audio data prior to encoding. The Bluetooth 00069 * standard specifically calls for a 1-to-8 interpolating 00070 * up-converter. While this reduces the overall compression of 00071 * the codec, this is required so that the encoder can accurately 00072 * compute the slope between adjacent audio samples and correctly 00073 * update its internal reference value. 00074 * 00075 * References: 00076 * 00077 * 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial, 00078 * Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF. 00079 * 00080 * 2. Specification of The Bluetooth System 00081 * Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf. 00082 * 00083 * 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002. 00084 * Bluetooth Voice Simulink® Model, Available: 00085 * http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html 00086 */ 00087 class VOCODER_API cvsd_encode_sb : virtual public sync_decimator 00088 { 00089 public: 00090 // gr::vocoder::cvsd_encode_sb::sptr 00091 typedef boost::shared_ptr<cvsd_encode_sb> sptr; 00092 00093 /*! 00094 * \brief Constructor parameters to initialize the CVSD encoder. 00095 * The default values are modeled after the Bluetooth standard and 00096 * should not be changed except by an advanced user 00097 * 00098 * \param min_step Minimum step size used to update the internal reference. Default: "10" 00099 * \param max_step Maximum step size used to update the internal reference. Default: "1280" 00100 * \param step_decay Decay factor applied to step size when there is not a run of J output 1s or 0s. 00101 * Default: "0.9990234375" (i.e. 1-1/1024) 00102 * \param accum_decay Decay factor applied to the internal reference during every interation of the codec. 00103 * Default: "0.96875" (i.e. 1-1/32) 00104 * \param K; Size of shift register; the number of output bits remembered by codec (must be <= to 32). 00105 * Default: "32" 00106 * \param J; Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. 00107 * Default: "4" 00108 * \param pos_accum_max Maximum integer value allowed for the internal reference. 00109 * Default: "32767" (2^15 - 1 or MAXSHORT) 00110 * \param neg_accum_max Minimum integer value allowed for the internal reference. 00111 * Default: "-32767" (-2^15 + 1 or MINSHORT+1) 00112 */ 00113 static sptr make(short min_step=10, short max_step=1280, 00114 double step_decay=0.9990234375, double accum_decay= 0.96875, 00115 int K=32, int J=4, 00116 short pos_accum_max=32767, short neg_accum_max=-32767); 00117 00118 virtual short min_step() = 0; 00119 virtual short max_step() = 0; 00120 virtual double step_decay() = 0; 00121 virtual double accum_decay() = 0; 00122 virtual int K() = 0; 00123 virtual int J() = 0; 00124 virtual short pos_accum_max() = 0; 00125 virtual short neg_accum_max() = 0; 00126 }; 00127 00128 } /* namespace vocoder */ 00129 } /* namespace gr */ 00130 00131 #endif /* INCLUDED_VOCODER_CVSD_ENCODE_SB_H */