diff options
Diffstat (limited to 'gr-vocoder/include/vocoder_cvsd_encode_sb.h')
| -rw-r--r-- | gr-vocoder/include/vocoder_cvsd_encode_sb.h | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/gr-vocoder/include/vocoder_cvsd_encode_sb.h b/gr-vocoder/include/vocoder_cvsd_encode_sb.h new file mode 100644 index 000000000..da09b3927 --- /dev/null +++ b/gr-vocoder/include/vocoder_cvsd_encode_sb.h @@ -0,0 +1,173 @@ +/* -*- 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_VOCODER_CVSD_ENCODER_SB_H +#define INCLUDED_VOCODER_CVSD_ENCODER_SB_H + +#include <gr_sync_decimator.h> + +class vocoder_cvsd_encode_sb; + +typedef boost::shared_ptr<vocoder_cvsd_encode_sb> vocoder_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) + * + */ + +vocoder_cvsd_encode_sb_sptr vocoder_make_cvsd_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_blk + * + * 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 vocoder_cvsd_encode_sb : public gr_sync_decimator +{ +private: + friend vocoder_cvsd_encode_sb_sptr vocoder_make_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); + + vocoder_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: + ~vocoder_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_VOCODER_CVSD_ENCODE_SB_H */ |