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/* -*- c++ -*- */
/*
* Copyright 2007 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef INCLUDED_CVSD_ENCODER_SB_H
#define INCLUDED_CVSD_ENCODER_SB_H
#include <gr_sync_decimator.h>
class cvsd_encode_sb;
typedef boost::shared_ptr<cvsd_encode_sb> cvsd_encode_sb_sptr;
/*!
* \brief Constructor parameters to initialize the CVSD encoder. The default
* values are modeled after the Bluetooth standard and should not be changed
* except by an advanced user
*
* \param min_step Minimum step size used to update the internal reference. Default: "10"
* \param max_step Maximum step size used to update the internal reference. Default: "1280"
* \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)
* \param accum_decay Decay factor applied to the internal reference during every interation of the codec. Default: "0.96875" (i.e. 1-1/32)
* \param K; Size of shift register; the number of output bits remembered by codec (must be less or equal to 32). Default: "32"
* \param J; Number of bits in the shift register that are equal; i.e. the size of a run of 1s, 0s. Default: "4"
* \param pos_accum_max Maximum integer value allowed for the internal reference. Default: "32767" (2^15 - 1 or MAXSHORT)
* \param neg_accum_max Minimum integer value allowed for the internal reference. Default: "-32767" (-2^15 + 1 or MINSHORT+1)
*
*/
cvsd_encode_sb_sptr cvsd_make_encode_sb (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);
/*!
* \brief This block performs CVSD audio encoding. Its design and implementation
* is modeled after the CVSD encoder/decoder specifications defined in the
* Bluetooth standard.
*
* \ingroup vocoder
*
* CVSD is a method for encoding speech that seeks to reduce the
* bandwidth required for digital voice transmission. CVSD takes
* advantage of strong correlation between samples, quantizing the
* difference in amplitude between two consecutive samples. This
* difference requires fewer quantization levels as compared to other
* methods that quantize the actual amplitude level, reducing the
* bandwidth. CVSD employs a two level quantizer (one bit) and an
* adaptive algorithm that allows for continuous step size adjustment.
*
* The coder can represent low amplitude signals with accuracy without
* sacrificing performance on large amplitude signals, a trade off that
* occurs in some non-adaptive modulations.
*
* The CVSD encoder effectively provides 8-to-1 compression. More
* specifically, each incoming audio sample is compared to an internal
* reference value. If the input is greater or equal to the reference,
* the encoder outputs a "1" bit. If the input is less than the reference,
* the encoder outputs a "0" bit. The reference value is then updated
* accordingly based on the frequency of outputted "1" or "0" bits. By
* grouping 8 outputs bits together, the encoder essentially produce one
* output byte for every 8 input audio samples.
*
* This encoder requires that input audio samples are 2-byte short signed
* integers. The result bandwidth conversion, therefore, is 16 input bytes
* of raw audio data to 1 output byte of encoded audio data.
*
* The CVSD encoder module must be prefixed by an up-converter to over-sample
* the audio data prior to encoding. The Bluetooth standard specifically
* calls for a 1-to-8 interpolating up-converter. While this reduces the
* overall compression of the codec, this is required so that the encoder
* can accurately compute the slope between adjacent audio samples and
* correctly update its internal reference value.
*
* References:
*
* 1. Continuously Variable Slope Delta Modulation (CVSD) A Tutorial,
* Available: http://www.eetkorea.com/ARTICLES/2003AUG/A/2003AUG29_NTEK_RFD_AN02.PDF.
*
* 2. Specification of The Bluetooth System
* Available: http://grouper.ieee.org/groups/802/15/Bluetooth/core_10_b.pdf.
*
* 3. McGarrity, S., Bluetooth Full Duplex Voice and Data Transmission. 2002.
* Bluetooth Voice Simulink® Model, Available:
* http://www.mathworks.com/company/newsletters/digest/nov01/bluetooth.html
*
*/
class cvsd_encode_sb : public gr_sync_decimator
{
private:
friend cvsd_encode_sb_sptr cvsd_make_encode_sb (short min_step,
short max_step,
double step_decay,
double accum_decay,
int K,
int J,
short pos_accum_max,
short neg_accum_max);
cvsd_encode_sb (short min_step, short max_step, double step_decay,
double accum_decay, int K, int J,
short pos_accum_max, short neg_accum_max);
//! Member functions required by the encoder/decoder
//! \brief Rounding function specific to CVSD
//! \return the input value rounded to the nearest integer
int cvsd_round(double input);
//! \brief A power function specific to CVSD data formats
//! \return (radix)^power, where radix and power are short integers
unsigned int cvsd_pow (short radix, short power);
//! \brief Sums number of 1's in the input
//! \return the number of 1s in the four bytes of an input unsigned integer
unsigned char cvsd_bitwise_sum (unsigned int input);
// Members variables related to the CVSD encoder use to update interal reference value
short d_min_step;
short d_max_step;
double d_step_decay;
double d_accum_decay;
int d_K; //!< \brief Size of shift register; the number of output bits remembered in shift register
int d_J; //!< \brief Number of bits in the shift register that are equal; size of run of 1s, 0s
short d_pos_accum_max;
short d_neg_accum_max;
int d_accum; //!< \brief Current value of internal reference
int d_loop_counter; //!< \brief Current value of the loop counter
unsigned int d_runner; //!< \brief Current value of the shift register
short d_stepsize; //!< \brief Current value of the step sizer
public:
~cvsd_encode_sb (); // public destructor
short min_step() { return d_min_step; }
short max_step() { return d_max_step; }
double step_decay() { return d_step_decay; }
double accum_decay() { return d_accum_decay; }
int K() { return d_K; }
int J() { return d_J; }
short pos_accum_max() { return d_pos_accum_max; }
short neg_accum_max() { return d_neg_accum_max; }
int work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items);
};
#endif /* INCLUDED_CVSD_ENCODE_SB_H */
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