GNU Radio 3.6.4.1 C++ API
vocoder_cvsd_encode_sb.h
Go to the documentation of this file.
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/* -*- c++ -*- */
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/*
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* Copyright 2007 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_ENCODER_SB_H
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#define INCLUDED_VOCODER_CVSD_ENCODER_SB_H
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#include <
vocoder_api.h
>
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#include <
gr_sync_decimator.h
>
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class
vocoder_cvsd_encode_sb
;
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typedef
boost::shared_ptr<vocoder_cvsd_encode_sb>
vocoder_cvsd_encode_sb_sptr
;
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/*!
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* \brief Constructor parameters to initialize the CVSD encoder. The
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* default values are modeled after the Bluetooth standard and should
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* not be changed except by an advanced user
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*
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* \ingroup vocoder_blk
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*
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* \param min_step Minimum step size used to update the internal reference. Default: "10"
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* \param max_step Maximum step size used to update the internal reference. 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. 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. 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 less or equal to 32). 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. Default: "4"
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* \param pos_accum_max Maximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT)
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* \param neg_accum_max Minimum integer value allowed for the internal reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1)
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*
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*/
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VOCODER_API
vocoder_cvsd_encode_sb_sptr
vocoder_make_cvsd_encode_sb
(
short
min_step
=10,
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short
max_step
=1280,
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double
step_decay
=0.9990234375,
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double
accum_decay
= 0.96875,
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int
K
=32,
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int
J
=4,
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short
pos_accum_max
=32767,
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short
neg_accum_max
=-32767);
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/*!
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* \brief This block performs CVSD audio encoding. Its design and implementation
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* is modeled after the CVSD encoder/decoder specifications defined in the
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* Bluetooth standard.
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*
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* \ingroup vocoder_blk
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*
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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 other
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* methods that quantize the actual amplitude level, reducing the
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* bandwidth. CVSD employs a two level quantizer (one bit) and an
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* adaptive algorithm that allows for continuous step size adjustment.
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*
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* The coder can represent low amplitude signals with accuracy without
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* sacrificing performance on large amplitude signals, a trade off that
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* occurs in some non-adaptive modulations.
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*
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* The CVSD encoder effectively provides 8-to-1 compression. More
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* specifically, each incoming audio sample is compared to an internal
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* reference value. If the input is greater or equal to the reference,
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* the encoder outputs a "1" bit. If the input is less than the reference,
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* the encoder outputs a "0" bit. The reference value is then updated
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* accordingly based on the frequency of outputted "1" or "0" bits. By
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* grouping 8 outputs bits together, the encoder essentially produce one
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* output byte for every 8 input audio samples.
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*
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* This encoder requires that input audio samples are 2-byte short signed
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* integers. The result bandwidth conversion, therefore, is 16 input bytes
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* of raw audio data to 1 output byte of encoded audio data.
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*
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* The CVSD encoder module must be prefixed by an up-converter to over-sample
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* the audio data prior to encoding. The Bluetooth standard specifically
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* calls for a 1-to-8 interpolating up-converter. While this reduces the
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* overall compression of the codec, this is required so that the encoder
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* can accurately compute the slope between adjacent audio samples and
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* correctly update its internal reference value.
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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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*/
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class
VOCODER_API
vocoder_cvsd_encode_sb
:
public
gr_sync_decimator
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{
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private
:
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friend
VOCODER_API
vocoder_cvsd_encode_sb_sptr
vocoder_make_cvsd_encode_sb
(
short
min_step,
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short
max_step,
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double
step_decay,
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double
accum_decay,
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int
K,
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int
J,
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short
pos_accum_max,
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short
neg_accum_max);
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vocoder_cvsd_encode_sb
(
short
min_step,
short
max_step,
double
step_decay,
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double
accum_decay,
int
K,
int
J,
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short
pos_accum_max,
short
neg_accum_max);
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//! Member functions required by the encoder/decoder
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//! \brief Rounding function specific to CVSD
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//! \return the input value rounded to the nearest integer
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int
cvsd_round(
double
input);
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//! \brief A power function specific to CVSD data formats
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//! \return (radix)^power, where radix and power are short integers
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unsigned
int
cvsd_pow (
short
radix,
short
power);
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//! \brief Sums number of 1's in the input
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//! \return the number of 1s in the four bytes of an input unsigned integer
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unsigned
char
cvsd_bitwise_sum (
unsigned
int
input);
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// Members variables related to the CVSD encoder use to update interal reference value
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short
d_min_step;
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short
d_max_step;
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double
d_step_decay;
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double
d_accum_decay;
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int
d_K;
//!< \brief Size of shift register; the number of output bits remembered in shift register
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int
d_J;
//!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
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short
d_pos_accum_max;
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short
d_neg_accum_max;
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int
d_accum;
//!< \brief Current value of internal reference
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int
d_loop_counter;
//!< \brief Current value of the loop counter
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unsigned
int
d_runner;
//!< \brief Current value of the shift register
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short
d_stepsize;
//!< \brief Current value of the step sizer
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public
:
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~
vocoder_cvsd_encode_sb
();
// public destructor
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short
min_step
() {
return
d_min_step; }
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short
max_step
() {
return
d_max_step; }
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double
step_decay
() {
return
d_step_decay; }
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double
accum_decay
() {
return
d_accum_decay; }
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int
K
() {
return
d_K; }
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int
J
() {
return
d_J; }
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short
pos_accum_max
() {
return
d_pos_accum_max; }
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short
neg_accum_max
() {
return
d_neg_accum_max; }
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int
work
(
int
noutput_items,
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gr_vector_const_void_star
&input_items,
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gr_vector_void_star
&output_items);
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};
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#endif
/* INCLUDED_VOCODER_CVSD_ENCODE_SB_H */
gr-vocoder
include
vocoder_cvsd_encode_sb.h
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