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
|
/* -*- c++ -*- */
/*
* Copyright 2007,2011 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_DECODE_BS_H
#define INCLUDED_VOCODER_CVSD_DECODE_BS_H
#include <gr_sync_interpolator.h>
class vocoder_cvsd_decode_bs;
typedef boost::shared_ptr<vocoder_cvsd_decode_bs> vocoder_cvsd_decode_bs_sptr;
/*!
* \brief Constructor parameters to initialize the CVSD decoder. The default
* values are modeled after the Bluetooth standard and should not be changed,
* except by an advanced user
*
* \ingroup vocoder_blk
*
* \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_cvsd_decode_bs_sptr vocoder_make_cvsd_decode_bs (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 decoding. 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 decoder effectively provides 1-to-8 decompression. More
* specifically, for each incoming input bit, the decoder outputs one
* audio sample. If the input is a "1" bit, the internal reference is
* increased appropriately and then outputted as the next estimated audio
* sample. If the input is a "0" bit, the internal reference is
* decreased appropriately and then likewise outputted as the next estimated
* audio sample. Grouping 8 input bits together, the encoder essentially
* produces 8 output audio samples for everyone one input byte.
*
* This decoder requires that output audio samples are 2-byte short signed
* integers. The result bandwidth conversion, therefore, is 1 byte of
* encoded audio data to 16 output bytes of raw audio data.
*
* The CVSD decoder module must be post-fixed by a down-converter to
* under-sample the audio data after decoding. The Bluetooth standard
* specifically calls for a 8-to-1 decimating down-converter. This is
* required so that so that output sampling rate equals the original input
* sampling rate present before the encoder. In all cases, the output
* down-converter rate must be the inverse of the input up-converter rate
* before the CVSD encoder.
*
* 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_cvsd_decode_bs : public gr_sync_interpolator
{
private:
friend vocoder_cvsd_decode_bs_sptr vocoder_make_cvsd_decode_bs (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_decode_bs (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);
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
unsigned int d_runner_mask; //!< \brief Value of the mask to access the last J bits of the shift register
short d_stepsize; //!< \brief Current value of the step sizer
public:
~vocoder_cvsd_decode_bs (); // 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_DECODE_BS_H */
|
