GNU Radio Manual and C++ API Reference 3.7.14.0
The Free & Open Software Radio Ecosystem
cvsd_decode_bs.h
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1/* -*- c++ -*- */
2/*
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4 *
5 * This file is part of GNU Radio
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22
23#ifndef INCLUDED_VOCODER_CVSD_DECODE_BS_H
24#define INCLUDED_VOCODER_CVSD_DECODE_BS_H
25
28
29namespace gr {
30namespace vocoder {
31
32/*!
33 * \brief This block performs CVSD audio decoding. Its design and
34 * implementation is modeled after the CVSD encoder/decoder
35 * specifications defined in the Bluetooth standard.
36 * \ingroup audio_blk
37 *
38 * \details
39 * CVSD is a method for encoding speech that seeks to reduce the
40 * bandwidth required for digital voice transmission. CVSD takes
41 * advantage of strong correlation between samples, quantizing the
42 * difference in amplitude between two consecutive samples. This
43 * difference requires fewer quantization levels as compared to
44 * other methods that quantize the actual amplitude level,
45 * reducing the bandwidth. CVSD employs a two level quantizer
46 * (one bit) and an adaptive algorithm that allows for continuous
47 * step size adjustment.
48 *
49 * The coder can represent low amplitude signals with accuracy
50 * without sacrificing performance on large amplitude signals, a
51 * trade off that occurs in some non-adaptive modulations.
52 *
53 * The CVSD decoder effectively provides 1-to-8 decompression.
54 * More specifically, for each incoming input bit, the decoder
55 * outputs one audio sample. If the input is a "1" bit, the
56 * internal reference is increased appropriately and then
57 * outputted as the next estimated audio sample. If the input is
58 * a "0" bit, the internal reference is decreased appropriately
59 * and then likewise outputted as the next estimated audio sample.
60 * Grouping 8 input bits together, the encoder essentially
61 * produces 8 output audio samples for everyone one input byte.
62 *
63 * This decoder requires that output audio samples are 2-byte
64 * short signed integers. The result bandwidth conversion,
65 * therefore, is 1 byte of encoded audio data to 16 output bytes
66 * of raw audio data.
67 *
68 * The CVSD decoder module must be post-fixed by a down-converter
69 * to under-sample the audio data after decoding. The Bluetooth
70 * standard specifically calls for a 8-to-1 decimating
71 * down-converter. This is required so that so that output
72 * sampling rate equals the original input sampling rate present
73 * before the encoder. In all cases, the output down-converter
74 * rate must be the inverse of the input up-converter rate before
75 * the CVSD encoder.
76 *
77 * References:
78 *
79 * 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
80 * Available:
81 * http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
82 *
83 * 2. Specification of The Bluetooth System
84 * Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
85 *
86 * 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
87 * Bluetooth Voice Simulink Model, Available:
88 * http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
89 */
91{
92public:
93 // gr::vocoder::cvsd_decode_bs::sptr
94 typedef boost::shared_ptr<cvsd_decode_bs> sptr;
95
96 /*!
97 * \brief Constructor parameters to initialize the CVSD decoder.
98 * The default values are modeled after the Bluetooth standard
99 * and should not be changed, except by an advanced user
100 *
101 * \param min_step Minimum step size used to update the internal reference.
102 * Default: "10"
103 * \param max_step Maximum step size used to update the internal reference.
104 * Default: "1280"
105 * \param step_decay Decay factor applied to step size when there is not a run of J
106 * output 1s or 0s. Default: "0.9990234375" (i.e. 1-1/1024) \param accum_decay Decay
107 * factor applied to the internal reference during every iteration of the codec.
108 * Default: "0.96875" (i.e. 1-1/32)
109 * \param K Size of shift register; the number of output bits remembered
110 * by codec (must be <= to 32). Default: "32" \param J Number of bits in
111 * the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
112 * \param pos_accum_max Maximum integer value allowed for the internal reference.
113 * Default: "32767" (2^15 - 1 or MAXSHORT)
114 * \param neg_accum_max Minimum integer value allowed for the internal reference.
115 * Default: "-32767" (-2^15 + 1 or MINSHORT+1)
116 */
117 static sptr make(short min_step = 10,
118 short max_step = 1280,
119 double step_decay = 0.9990234375,
120 double accum_decay = 0.96875,
121 int K = 32,
122 int J = 4,
123 short pos_accum_max = 32767,
124 short neg_accum_max = -32767);
125
126 virtual short min_step() = 0;
127 virtual short max_step() = 0;
128 virtual double step_decay() = 0;
129 virtual double accum_decay() = 0;
130 virtual int K() = 0;
131 virtual int J() = 0;
132 virtual short pos_accum_max() = 0;
133 virtual short neg_accum_max() = 0;
134};
135
136} /* namespace vocoder */
137} /* namespace gr */
138
139#endif /* INCLUDED_VOCODER_CVSD_DECODE_BS_H */
synchronous 1:N input to output with history
Definition: sync_interpolator.h:38
This block performs CVSD audio decoding. Its design and implementation is modeled after the CVSD enco...
Definition: cvsd_decode_bs.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 decoder. The default values are modeled after the Bluet...
virtual short min_step()=0
virtual double step_decay()=0
virtual short pos_accum_max()=0
virtual double accum_decay()=0
boost::shared_ptr< cvsd_decode_bs > sptr
Definition: cvsd_decode_bs.h:94
virtual short neg_accum_max()=0
virtual short max_step()=0
#define VOCODER_API
Definition: gr-vocoder/include/gnuradio/vocoder/api.h:30
Include this header to use the message passing features.
Definition: basic_block.h:45