1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
/* -*- c++ -*- */
/*
* Copyright 2007 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef INCLUDED_VOCODER_CVSD_ENCODER_SB_H
#define INCLUDED_VOCODER_CVSD_ENCODER_SB_H
#include <vocoder_api.h>
#include <gr_sync_decimator.h>
class vocoder_cvsd_encode_sb;
typedef boost::shared_ptr<vocoder_cvsd_encode_sb> vocoder_cvsd_encode_sb_sptr;
/*!
* \brief Constructor parameters to initialize the CVSD encoder. The default
* values are modeled after the Bluetooth standard and should not be changed
* except by an advanced user
*
* \param min_step Minimum step size used to update the internal reference. Default: "10"
* \param max_step Maximum step size used to update the internal reference. Default: "1280"
* \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)
* \param accum_decay Decay factor applied to the internal reference during every interation of the codec. Default: "0.96875" (i.e. 1-1/32)
* \param K; Size of shift register; the number of output bits remembered by codec (must be less or equal to 32). Default: "32"
* \param J; Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
* \param pos_accum_max Maximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT)
* \param neg_accum_max Minimum integer value allowed for the internal reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1)
*
*/
VOCODER_API vocoder_cvsd_encode_sb_sptr vocoder_make_cvsd_encode_sb(short min_step=10,
short max_step=1280,
double step_decay=0.9990234375,
double accum_decay= 0.96875,
int K=32,
int J=4,
short pos_accum_max=32767,
short neg_accum_max=-32767);
/*!
* \brief This block performs CVSD audio encoding. Its design and implementation
* is modeled after the CVSD encoder/decoder specifications defined in the
* Bluetooth standard.
*
* \ingroup vocoder_blk
*
* CVSD is a method for encoding speech that seeks to reduce the
* bandwidth required for digital voice transmission. CVSD takes
* advantage of strong correlation between samples, quantizing the
* difference in amplitude between two consecutive samples. This
* difference requires fewer quantization levels as compared to other
* methods that quantize the actual amplitude level, reducing the
* bandwidth. CVSD employs a two level quantizer (one bit) and an
* adaptive algorithm that allows for continuous step size adjustment.
*
* The coder can represent low amplitude signals with accuracy without
* sacrificing performance on large amplitude signals, a trade off that
* occurs in some non-adaptive modulations.
*
* The CVSD encoder effectively provides 8-to-1 compression. More
* specifically, each incoming audio sample is compared to an internal
* reference value. If the input is greater or equal to the reference,
* the encoder outputs a "1" bit. If the input is less than the reference,
* the encoder outputs a "0" bit. The reference value is then updated
* accordingly based on the frequency of outputted "1" or "0" bits. By
* grouping 8 outputs bits together, the encoder essentially produce one
* output byte for every 8 input audio samples.
*
* This encoder requires that input audio samples are 2-byte short signed
* integers. The result bandwidth conversion, therefore, is 16 input bytes
* of raw audio data to 1 output byte of encoded audio data.
*
* The CVSD encoder module must be prefixed by an up-converter to over-sample
* the audio data prior to encoding. The Bluetooth standard specifically
* calls for a 1-to-8 interpolating up-converter. While this reduces the
* overall compression of the codec, this is required so that the encoder
* can accurately compute the slope between adjacent audio samples and
* correctly update its internal reference value.
*
* References:
*
* 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
* Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
*
* 2. Specification of The Bluetooth System
* Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
*
* 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
* Bluetooth Voice Simulink® Model, Available:
* http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
*
*/
class VOCODER_API vocoder_cvsd_encode_sb : public gr_sync_decimator
{
private:
friend VOCODER_API vocoder_cvsd_encode_sb_sptr vocoder_make_cvsd_encode_sb(short min_step,
short max_step,
double step_decay,
double accum_decay,
int K,
int J,
short pos_accum_max,
short neg_accum_max);
vocoder_cvsd_encode_sb(short min_step, short max_step, double step_decay,
double accum_decay, int K, int J,
short pos_accum_max, short neg_accum_max);
//! Member functions required by the encoder/decoder
//! \brief Rounding function specific to CVSD
//! \return the input value rounded to the nearest integer
int cvsd_round(double input);
//! \brief A power function specific to CVSD data formats
//! \return (radix)^power, where radix and power are short integers
unsigned int cvsd_pow (short radix, short power);
//! \brief Sums number of 1's in the input
//! \return the number of 1s in the four bytes of an input unsigned integer
unsigned char cvsd_bitwise_sum (unsigned int input);
// Members variables related to the CVSD encoder use to update interal reference value
short d_min_step;
short d_max_step;
double d_step_decay;
double d_accum_decay;
int d_K; //!< \brief Size of shift register; the number of output bits remembered in shift register
int d_J; //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
short d_pos_accum_max;
short d_neg_accum_max;
int d_accum; //!< \brief Current value of internal reference
int d_loop_counter; //!< \brief Current value of the loop counter
unsigned int d_runner; //!< \brief Current value of the shift register
short d_stepsize; //!< \brief Current value of the step sizer
public:
~vocoder_cvsd_encode_sb (); // public destructor
short min_step() { return d_min_step; }
short max_step() { return d_max_step; }
double step_decay() { return d_step_decay; }
double accum_decay() { return d_accum_decay; }
int K() { return d_K; }
int J() { return d_J; }
short pos_accum_max() { return d_pos_accum_max; }
short neg_accum_max() { return d_neg_accum_max; }
int work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items);
};
#endif /* INCLUDED_VOCODER_CVSD_ENCODE_SB_H */
|
