GNU Radio Manual and C++ API Reference 3.8.5.0
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cvsd_encode_sb.h
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1/* -*- c++ -*- */
2/*
3 * Copyright 2007,2013 Free Software Foundation, Inc.
4 *
5 * This file is part of GNU Radio
6 *
7 * GNU Radio is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 3, or (at your option)
10 * any later version.
11 *
12 * GNU Radio is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with GNU Radio; see the file COPYING. If not, write to
19 * the Free Software Foundation, Inc., 51 Franklin Street,
20 * Boston, MA 02110-1301, USA.
21 */
22#ifndef INCLUDED_VOCODER_CVSD_ENCODER_SB_H
23#define INCLUDED_VOCODER_CVSD_ENCODER_SB_H
24
27
28namespace gr {
29namespace vocoder {
30
31/*!
32 * \brief This block performs CVSD audio encoding. Its design and
33 * implementation is modeled after the CVSD encoder/decoder
34 * specifications defined in the Bluetooth standard.
35 * \ingroup audio_blk
36 *
37 * \details
38 * CVSD is a method for encoding speech that seeks to reduce the
39 * bandwidth required for digital voice transmission. CVSD takes
40 * advantage of strong correlation between samples, quantizing the
41 * difference in amplitude between two consecutive samples. This
42 * difference requires fewer quantization levels as compared to
43 * other methods that quantize the actual amplitude level,
44 * reducing the bandwidth. CVSD employs a two level quantizer
45 * (one bit) and an adaptive algorithm that allows for continuous
46 * step size adjustment.
47 *
48 * The coder can represent low amplitude signals with accuracy
49 * without sacrificing performance on large amplitude signals, a
50 * trade off that occurs in some non-adaptive modulations.
51 *
52 * The CVSD encoder effectively provides 8-to-1 compression. More
53 * specifically, each incoming audio sample is compared to an
54 * internal reference value. If the input is greater or equal to
55 * the reference, the encoder outputs a "1" bit. If the input is
56 * less than the reference, the encoder outputs a "0" bit. The
57 * reference value is then updated accordingly based on the
58 * frequency of outputted "1" or "0" bits. By grouping 8 outputs
59 * bits together, the encoder essentially produce one output byte
60 * for every 8 input audio samples.
61 *
62 * This encoder requires that input audio samples are 2-byte short
63 * signed integers. The result bandwidth conversion, therefore,
64 * is 16 input bytes of raw audio data to 1 output byte of encoded
65 * audio data.
66 *
67 * The CVSD encoder module must be prefixed by an up-converter to
68 * over-sample the audio data prior to encoding. The Bluetooth
69 * standard specifically calls for a 1-to-8 interpolating
70 * up-converter. While this reduces the overall compression of
71 * the codec, this is required so that the encoder can accurately
72 * compute the slope between adjacent audio samples and correctly
73 * update its internal reference value.
74 *
75 * References:
76 *
77 * 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
78 * Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
79 *
80 * 2. Specification of The Bluetooth System
81 * Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
82 *
83 * 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
84 * Bluetooth Voice Simulink Model, Available:
85 * http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
86 */
88{
89public:
90 // gr::vocoder::cvsd_encode_sb::sptr
91 typedef boost::shared_ptr<cvsd_encode_sb> sptr;
92
93 /*!
94 * \brief Constructor parameters to initialize the CVSD encoder.
95 * The default values are modeled after the Bluetooth standard and
96 * should not be changed except by an advanced user
97 *
98 * \param min_step Minimum step size used to update the internal reference.
99 * Default: "10" \param max_step Maximum step size used to update the internal
100 * reference. Default: "1280" \param step_decay Decay factor applied to step size
101 * when there is not a run of J output 1s or 0s. Default: "0.9990234375" (i.e.
102 * 1-1/1024) \param accum_decay Decay factor applied to the internal reference
103 * during every iteration of the codec. Default: "0.96875" (i.e. 1-1/32) \param K
104 * Size of shift register; the number of output bits remembered by codec (must be <=
105 * to 32). Default: "32" \param J Number of bits in the shift register
106 * that are equal; i.e. the size of a run of 1s, 0s. Default: "4" \param pos_accum_max
107 * Maximum integer value allowed for the internal reference. Default: "32767" (2^15 -
108 * 1 or MAXSHORT) \param neg_accum_max Minimum integer value allowed for the internal
109 * reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1)
110 */
111 static sptr make(short min_step = 10,
112 short max_step = 1280,
113 double step_decay = 0.9990234375,
114 double accum_decay = 0.96875,
115 int K = 32,
116 int J = 4,
117 short pos_accum_max = 32767,
118 short neg_accum_max = -32767);
119
120 virtual short min_step() = 0;
121 virtual short max_step() = 0;
122 virtual double step_decay() = 0;
123 virtual double accum_decay() = 0;
124 virtual int K() = 0;
125 virtual int J() = 0;
126 virtual short pos_accum_max() = 0;
127 virtual short neg_accum_max() = 0;
128};
129
130} /* namespace vocoder */
131} /* namespace gr */
132
133#endif /* INCLUDED_VOCODER_CVSD_ENCODE_SB_H */
synchronous N:1 input to output with history
Definition sync_decimator.h:38
This block performs CVSD audio encoding. Its design and implementation is modeled after the CVSD enco...
Definition cvsd_encode_sb.h:88
virtual double accum_decay()=0
virtual short min_step()=0
virtual short max_step()=0
virtual short neg_accum_max()=0
boost::shared_ptr< cvsd_encode_sb > sptr
Definition cvsd_encode_sb.h:91
static sptr make(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)
Constructor parameters to initialize the CVSD encoder. The default values are modeled after the Bluet...
virtual double step_decay()=0
virtual short pos_accum_max()=0
#define VOCODER_API
Definition gr-vocoder/include/gnuradio/vocoder/api.h:30
GNU Radio logging wrapper for log4cpp library (C++ port of log4j)
Definition basic_block.h:46