GNU Radio 3.6.1 C++ API
vocoder_cvsd_decode_bs.h
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1 /* -*- c++ -*- */
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22 
23 #ifndef INCLUDED_VOCODER_CVSD_DECODE_BS_H
24 #define INCLUDED_VOCODER_CVSD_DECODE_BS_H
25 
26 #include <vocoder_api.h>
27 #include <gr_sync_interpolator.h>
28 
30 
32 
33  /*!
34  * \brief Constructor parameters to initialize the CVSD decoder. The default
35  * values are modeled after the Bluetooth standard and should not be changed,
36  * except by an advanced user
37  *
38  * \ingroup vocoder_blk
39  *
40  * \param min_step Minimum step size used to update the internal reference. Default: "10"
41  * \param max_step Maximum step size used to update the internal reference. Default: "1280"
42  * \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)
43  * \param accum_decay Decay factor applied to the internal reference during every interation of the codec. Default: "0.96875" (i.e. 1-1/32)
44  * \param K; Size of shift register; the number of output bits remembered by codec (must be less or equal to 32). Default: "32"
45  * \param J; Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
46  * \param pos_accum_max Maximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT)
47  * \param neg_accum_max Minimum integer value allowed for the internal reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1)
48  *
49  */
51  short max_step=1280,
52  double step_decay=0.9990234375,
53  double accum_decay= 0.96875,
54  int K=32,
55  int J=4,
56  short pos_accum_max=32767,
57  short neg_accum_max=-32767);
58 
59 /*!
60  * \brief This block performs CVSD audio decoding. Its design and implementation
61  * is modeled after the CVSD encoder/decoder specifications defined in the
62  * Bluetooth standard.
63  *
64  * \ingroup vocoder_blk
65  *
66  * CVSD is a method for encoding speech that seeks to reduce the
67  * bandwidth required for digital voice transmission. CVSD takes
68  * advantage of strong correlation between samples, quantizing the
69  * difference in amplitude between two consecutive samples. This
70  * difference requires fewer quantization levels as compared to other
71  * methods that quantize the actual amplitude level, reducing the
72  * bandwidth. CVSD employs a two level quantizer (one bit) and an
73  * adaptive algorithm that allows for continuous step size adjustment.
74  *
75  * The coder can represent low amplitude signals with accuracy without
76  * sacrificing performance on large amplitude signals, a trade off that
77  * occurs in some non-adaptive modulations.
78  *
79  * The CVSD decoder effectively provides 1-to-8 decompression. More
80  * specifically, for each incoming input bit, the decoder outputs one
81  * audio sample. If the input is a "1" bit, the internal reference is
82  * increased appropriately and then outputted as the next estimated audio
83  * sample. If the input is a "0" bit, the internal reference is
84  * decreased appropriately and then likewise outputted as the next estimated
85  * audio sample. Grouping 8 input bits together, the encoder essentially
86  * produces 8 output audio samples for everyone one input byte.
87  *
88  * This decoder requires that output audio samples are 2-byte short signed
89  * integers. The result bandwidth conversion, therefore, is 1 byte of
90  * encoded audio data to 16 output bytes of raw audio data.
91  *
92  * The CVSD decoder module must be post-fixed by a down-converter to
93  * under-sample the audio data after decoding. The Bluetooth standard
94  * specifically calls for a 8-to-1 decimating down-converter. This is
95  * required so that so that output sampling rate equals the original input
96  * sampling rate present before the encoder. In all cases, the output
97  * down-converter rate must be the inverse of the input up-converter rate
98  * before the CVSD encoder.
99  *
100  * References:
101  * 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
102  * Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
103  * 2. Specification of The Bluetooth System
104  * Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
105  * 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
106  * Bluetooth Voice Simulink® Model, Available:
107  * http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
108  *
109  */
110 
112 {
113 private:
115  short max_step,
116  double step_decay,
117  double accum_decay,
118  int K,
119  int J,
120  short pos_accum_max,
121  short neg_accum_max);
122 
123  vocoder_cvsd_decode_bs (short min_step, short max_step, double step_decay,
124  double accum_decay, int K, int J,
125  short pos_accum_max, short neg_accum_max);
126 
127  //! Member functions required by the encoder/decoder
128  //! \brief Rounding function specific to CVSD
129  //! \return the input value rounded to the nearest integer
130  int cvsd_round(double input);
131 
132  //! \brief A power function specific to CVSD data formats
133  //! \return (radix)^power, where radix and power are short integers
134  unsigned int cvsd_pow (short radix, short power);
135 
136  //! \brief Sums number of 1's in the input
137  //! \return the number of 1s in the four bytes of an input unsigned integer
138  unsigned char cvsd_bitwise_sum (unsigned int input);
139 
140  short d_min_step;
141  short d_max_step;
142  double d_step_decay;
143  double d_accum_decay;
144 
145  int d_K; //!< \brief Size of shift register; the number of output bits remembered in shift register
146  int d_J; //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
147 
148  short d_pos_accum_max;
149  short d_neg_accum_max;
150 
151  int d_accum; //!< \brief Current value of internal reference
152  int d_loop_counter; //!< \brief Current value of the loop counter
153  unsigned int d_runner; //!< \brief Current value of the shift register
154  unsigned int d_runner_mask; //!< \brief Value of the mask to access the last J bits of the shift register
155  short d_stepsize; //!< \brief Current value of the step sizer
156 
157  public:
158  ~vocoder_cvsd_decode_bs (); // public destructor
159 
160  short min_step() { return d_min_step; }
161  short max_step() { return d_max_step; }
162  double step_decay() { return d_step_decay; }
163  double accum_decay() { return d_accum_decay; }
164  int K() { return d_K; }
165  int J() { return d_J; }
166  short pos_accum_max() { return d_pos_accum_max; }
167  short neg_accum_max() { return d_neg_accum_max; }
168 
169  int work (int noutput_items,
170  gr_vector_const_void_star &input_items,
171  gr_vector_void_star &output_items);
172 };
173 
174 #endif /* INCLUDED_VOCODER_CVSD_DECODE_BS_H */