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cvsd_decode_bs.h
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/* -*- c++ -*- */
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/*
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* Copyright 2007,2011,2013 Free Software Foundation, Inc.
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*
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* This file is part of GNU Radio
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*
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* GNU Radio is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* GNU Radio is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU Radio; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifndef INCLUDED_VOCODER_CVSD_DECODE_BS_H
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#define INCLUDED_VOCODER_CVSD_DECODE_BS_H
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#include <
gnuradio/vocoder/api.h
>
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#include <
gnuradio/sync_interpolator.h
>
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namespace
gr {
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namespace
vocoder {
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/*!
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* \brief This block performs CVSD audio decoding. Its design and
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* implementation is modeled after the CVSD encoder/decoder
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* specifications defined in the Bluetooth standard.
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* \ingroup audio_blk
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*
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* \details
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* CVSD is a method for encoding speech that seeks to reduce the
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* bandwidth required for digital voice transmission. CVSD takes
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* advantage of strong correlation between samples, quantizing the
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* difference in amplitude between two consecutive samples. This
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* difference requires fewer quantization levels as compared to
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* other methods that quantize the actual amplitude level,
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* reducing the bandwidth. CVSD employs a two level quantizer
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* (one bit) and an adaptive algorithm that allows for continuous
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* step size adjustment.
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*
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* The coder can represent low amplitude signals with accuracy
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* without sacrificing performance on large amplitude signals, a
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* trade off that occurs in some non-adaptive modulations.
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*
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* The CVSD decoder effectively provides 1-to-8 decompression.
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* More specifically, for each incoming input bit, the decoder
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* outputs one audio sample. If the input is a "1" bit, the
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* internal reference is increased appropriately and then
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* outputted as the next estimated audio sample. If the input is
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* a "0" bit, the internal reference is decreased appropriately
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* and then likewise outputted as the next estimated audio sample.
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* Grouping 8 input bits together, the encoder essentially
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* produces 8 output audio samples for everyone one input byte.
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*
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* This decoder requires that output audio samples are 2-byte
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* short signed integers. The result bandwidth conversion,
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* therefore, is 1 byte of encoded audio data to 16 output bytes
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* of raw audio data.
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*
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* The CVSD decoder module must be post-fixed by a down-converter
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* to under-sample the audio data after decoding. The Bluetooth
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* standard specifically calls for a 8-to-1 decimating
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* down-converter. This is required so that so that output
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* sampling rate equals the original input sampling rate present
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* before the encoder. In all cases, the output down-converter
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* rate must be the inverse of the input up-converter rate before
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* the CVSD encoder.
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*
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* References:
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*
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* 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
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* Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
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*
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* 2. Specification of The Bluetooth System
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* Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
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*
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* 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
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* Bluetooth Voice Simulink Model, Available:
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* http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
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*/
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class
VOCODER_API
cvsd_decode_bs
:
virtual
public
sync_interpolator
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{
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public
:
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// gr::vocoder::cvsd_decode_bs::sptr
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typedef
boost::shared_ptr<cvsd_decode_bs>
sptr
;
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/*!
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* \brief Constructor parameters to initialize the CVSD decoder.
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* The default values are modeled after the Bluetooth standard
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* and should not be changed, except by an advanced user
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*
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* \param min_step Minimum step size used to update the internal reference.
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* Default: "10"
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* \param max_step Maximum step size used to update the internal reference.
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* Default: "1280"
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* \param step_decay Decay factor applied to step size when there is not a run of J output 1s or 0s.
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* Default: "0.9990234375" (i.e. 1-1/1024)
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* \param accum_decay Decay factor applied to the internal reference during every interation of the codec.
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* Default: "0.96875" (i.e. 1-1/32)
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* \param K Size of shift register; the number of output bits remembered by codec (must be <= to 32).
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* Default: "32"
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* \param J Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s.
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* Default: "4"
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* \param pos_accum_max Maximum integer value allowed for the internal reference.
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* Default: "32767" (2^15 - 1 or MAXSHORT)
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* \param neg_accum_max Minimum integer value allowed for the internal reference.
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* Default: "-32767" (-2^15 + 1 or MINSHORT+1)
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*/
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static
sptr
make(
short
min_step=10,
short
max_step=1280,
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double
step_decay=0.9990234375,
double
accum_decay= 0.96875,
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int
K=32,
int
J=4,
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short
pos_accum_max=32767,
short
neg_accum_max=-32767);
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virtual
short
min_step() = 0;
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virtual
short
max_step() = 0;
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virtual
double
step_decay() = 0;
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virtual
double
accum_decay() = 0;
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virtual
int
K() = 0;
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virtual
int
J() = 0;
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virtual
short
pos_accum_max() = 0;
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virtual
short
neg_accum_max() = 0;
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};
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}
/* namespace vocoder */
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}
/* namespace gr */
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#endif
/* INCLUDED_VOCODER_CVSD_DECODE_BS_H */
gr-vocoder
include
gnuradio
vocoder
cvsd_decode_bs.h
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