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22 #ifndef INCLUDED_CVSD_ENCODER_SB_H
23 #define INCLUDED_CVSD_ENCODER_SB_H
25 #include <gr_sync_decimator.h>
29 typedef boost::shared_ptr<cvsd_encode_sb> cvsd_encode_sb_sptr;
32 * \brief Constructor parameters to initialize the CVSD encoder. 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_encode_sb_sptr cvsd_make_encode_sb (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 encoding. 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 encoder effectively provides 8-to-1 compression. More
77 * specifically, each incoming audio sample is compared to an internal
78 * reference value. If the input is greater or equal to the reference,
79 * the encoder outputs a "1" bit. If the input is less than the reference,
80 * the encoder outputs a "0" bit. The reference value is then updated
81 * accordingly based on the frequency of outputted "1" or "0" bits. By
82 * grouping 8 outputs bits together, the encoder essentially produce one
83 * output byte for every 8 input audio samples.
85 * This encoder requires that input audio samples are 2-byte short signed
86 * integers. The result bandwidth conversion, therefore, is 16 input bytes
87 * of raw audio data to 1 output byte of encoded audio data.
89 * The CVSD encoder module must be prefixed by an up-converter to over-sample
90 * the audio data prior to encoding. The Bluetooth standard specifically
91 * calls for a 1-to-8 interpolating up-converter. While this reduces the
92 * overall compression of the codec, this is required so that the encoder
93 * can accurately compute the slope between adjacent audio samples and
94 * correctly update its internal reference value.
98 * 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
99 * Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
101 * 2. Specification of The Bluetooth System
102 * Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
104 * 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
105 * Bluetooth Voice Simulink® Model, Available:
106 * http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
110 class cvsd_encode_sb : public gr_sync_decimator
113 friend cvsd_encode_sb_sptr cvsd_make_encode_sb (short min_step,
120 short neg_accum_max);
122 cvsd_encode_sb (short min_step, short max_step, double step_decay,
123 double accum_decay, int K, int J,
124 short pos_accum_max, short neg_accum_max);
126 //! Member functions required by the encoder/decoder
127 //! \brief Rounding function specific to CVSD
128 //! \return the input value rounded to the nearest integer
129 int cvsd_round(double input);
131 //! \brief A power function specific to CVSD data formats
132 //! \return (radix)^power, where radix and power are short integers
133 unsigned int cvsd_pow (short radix, short power);
135 //! \brief Sums number of 1's in the input
136 //! \return the number of 1s in the four bytes of an input unsigned integer
137 unsigned char cvsd_bitwise_sum (unsigned int input);
139 // Members variables related to the CVSD encoder use to update interal reference value
143 double d_accum_decay;
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
148 short d_pos_accum_max;
149 short d_neg_accum_max;
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 short d_stepsize; //!< \brief Current value of the step sizer
157 ~cvsd_encode_sb (); // public destructor
159 short min_step() { return d_min_step; }
160 short max_step() { return d_max_step; }
161 double step_decay() { return d_step_decay; }
162 double accum_decay() { return d_accum_decay; }
163 int K() { return d_K; }
164 int J() { return d_J; }
165 short pos_accum_max() { return d_pos_accum_max; }
166 short neg_accum_max() { return d_neg_accum_max; }
168 int work (int noutput_items,
169 gr_vector_const_void_star &input_items,
170 gr_vector_void_star &output_items);
173 #endif /* INCLUDED_CVSD_ENCODE_SB_H */