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