| 1 | /* |
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| 2 | Copyright (C) 2003-2015 Paul Brossier <piem@aubio.org> |
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| 3 | |
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| 4 | This file is part of aubio. |
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| 5 | |
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| 6 | aubio is free software: you can redistribute it and/or modify |
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| 7 | it under the terms of the GNU General Public License as published by |
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| 8 | the Free Software Foundation, either version 3 of the License, or |
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| 9 | (at your option) any later version. |
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| 10 | |
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| 11 | aubio is distributed in the hope that it will be useful, |
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| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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| 14 | GNU General Public License for more details. |
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| 15 | |
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| 16 | You should have received a copy of the GNU General Public License |
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| 17 | along with aubio. If not, see <http://www.gnu.org/licenses/>. |
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| 18 | |
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| 19 | */ |
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| 20 | |
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| 21 | #ifndef AUBIO_FILTER_C_DESIGN_H |
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| 22 | #define AUBIO_FILTER_C_DESIGN_H |
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| 23 | |
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| 24 | /** \file |
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| 25 | |
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| 26 | C-weighting filter coefficients |
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| 27 | |
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| 28 | This file creates a C-weighting digital filter, which reduces low and high |
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| 29 | frequencies and enhance the middle ones to reflect the ability of the human |
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| 30 | hearing. |
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| 31 | |
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| 32 | The implementation is based on the following standard: |
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| 33 | |
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| 34 | - IEC/CD 1672: Electroacoustics-Sound Level Meters, IEC, Geneva, Nov. 1996, |
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| 35 | for A- and C-weighting filters. |
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| 36 | |
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| 37 | See also: |
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| 38 | |
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| 39 | - <a href="http://en.wikipedia.org/wiki/A-weighting">A-Weighting on |
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| 40 | Wikipedia</a> |
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| 41 | - <a href="http://en.wikipedia.org/wiki/Weighting_filter">Weighting filter on |
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| 42 | Wikipedia</a> |
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| 43 | - <a href="http://www.mathworks.com/matlabcentral/fileexchange/69">Christophe |
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| 44 | Couvreur's 'octave' toolbox</a> |
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| 45 | |
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| 46 | The coefficients in this file have been computed using Christophe Couvreur's |
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| 47 | scripts in octave 3.0 (debian package 1:3.0.5-6+b2 with octave-signal |
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| 48 | 1.0.9-1+b1 on i386), with <pre> [b, a] = cdsign(1/Fs) </pre> for various |
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| 49 | sampling frequencies (8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000, |
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| 50 | 88200, 96000, and 192000 Hz). |
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| 51 | |
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| 52 | The sampling frequency should normally be higher than 20kHz, but most common |
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| 53 | file sampling rates have been included for completeness. |
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| 54 | |
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| 55 | \example temporal/test-c_weighting.c |
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| 56 | |
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| 57 | */ |
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| 58 | |
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| 59 | #ifdef __cplusplus |
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| 60 | extern "C" { |
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| 61 | #endif |
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| 62 | |
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| 63 | /** create new C-design filter |
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| 64 | |
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| 65 | \param samplerate sampling frequency of the signal to filter. Should be one of |
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| 66 | 8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000, 88200, 96000, and |
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| 67 | 192000 Hz |
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| 68 | |
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| 69 | \return a new filter object |
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| 70 | |
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| 71 | */ |
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| 72 | aubio_filter_t *new_aubio_filter_c_weighting (uint_t samplerate); |
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| 73 | |
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| 74 | /** set feedback and feedforward coefficients of a C-weighting filter |
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| 75 | |
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| 76 | \param f filter object to get coefficients from |
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| 77 | \param samplerate sampling frequency of the signal to filter. Should be one of |
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| 78 | 8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000, 88200, 96000, and |
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| 79 | 192000 Hz |
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| 80 | |
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| 81 | */ |
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| 82 | uint_t aubio_filter_set_c_weighting (aubio_filter_t * f, uint_t samplerate); |
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| 83 | |
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| 84 | #ifdef __cplusplus |
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| 85 | } |
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| 86 | #endif |
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| 87 | |
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| 88 | #endif /* AUBIO_FILTER_C_DESIGN_H */ |
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