GNU Radio 3.7.1-34 C++ API
cvsd_encode_sb.h
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/* -*- c++ -*- */
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/*
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* Copyright 2007,2013 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_ENCODER_SB_H
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#define INCLUDED_VOCODER_CVSD_ENCODER_SB_H
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#include <
gnuradio/vocoder/api.h
>
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#include <
gnuradio/sync_decimator.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 encoding. 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 encoder effectively provides 8-to-1 compression. More
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* specifically, each incoming audio sample is compared to an
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* internal reference value. If the input is greater or equal to
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* the reference, the encoder outputs a "1" bit. If the input is
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* less than the reference, the encoder outputs a "0" bit. The
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* reference value is then updated accordingly based on the
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* frequency of outputted "1" or "0" bits. By grouping 8 outputs
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* bits together, the encoder essentially produce one output byte
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* 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
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* signed integers. The result bandwidth conversion, therefore,
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* is 16 input bytes of raw audio data to 1 output byte of encoded
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* audio data.
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*
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* The CVSD encoder module must be prefixed by an up-converter to
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* over-sample the audio data prior to encoding. The Bluetooth
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* standard specifically calls for a 1-to-8 interpolating
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* up-converter. While this reduces the overall compression of
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* the codec, this is required so that the encoder can accurately
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* compute the slope between adjacent audio samples and correctly
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* 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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class
VOCODER_API
cvsd_encode_sb
:
virtual
public
sync_decimator
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{
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public
:
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// gr::vocoder::cvsd_encode_sb::sptr
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typedef
boost::shared_ptr<cvsd_encode_sb>
sptr
;
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/*!
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* \brief Constructor parameters to initialize the CVSD encoder.
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* The default values are modeled after the Bluetooth standard and
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* 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. 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.
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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_ENCODE_SB_H */
gnuradio
gr-vocoder
include
gnuradio
vocoder
cvsd_encode_sb.h
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