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Diffstat (limited to 'gr-vocoder/include/gnuradio/vocoder/cvsd_encode_sb.h')
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diff --git a/gr-vocoder/include/gnuradio/vocoder/cvsd_encode_sb.h b/gr-vocoder/include/gnuradio/vocoder/cvsd_encode_sb.h new file mode 100644 index 0000000000..7b7cea712e --- /dev/null +++ b/gr-vocoder/include/gnuradio/vocoder/cvsd_encode_sb.h @@ -0,0 +1,131 @@ +/* -*- c++ -*- */ +/* + * Copyright 2007,2013 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 <gnuradio/vocoder/api.h> +#include <gnuradio/sync_decimator.h> + +namespace gr { + namespace vocoder { + + /*! + * \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 audio_blk + * + * \details + * 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_API cvsd_encode_sb : virtual public sync_decimator + { + public: + // gr::vocoder::cvsd_encode_sb::sptr + typedef boost::shared_ptr<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 <= 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) + */ + static sptr make(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); + + virtual short min_step() = 0; + virtual short max_step() = 0; + virtual double step_decay() = 0; + virtual double accum_decay() = 0; + virtual int K() = 0; + virtual int J() = 0; + virtual short pos_accum_max() = 0; + virtual short neg_accum_max() = 0; + }; + + } /* namespace vocoder */ +} /* namespace gr */ + +#endif /* INCLUDED_VOCODER_CVSD_ENCODE_SB_H */ |