1 | /* |
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2 | Copyright (C) 2003-2009 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 FILTER_H |
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22 | #define FILTER_H |
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23 | |
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24 | /** \file |
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25 | |
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26 | Digital filter |
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27 | |
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28 | This object stores a digital filter of order \f$n\f$ for \f$c\f$ channels. |
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29 | It contains the following data: |
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30 | - \f$ n*1 b_i \f$ feedforward coefficients |
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31 | - \f$ n*1 a_i \f$ feedback coefficients |
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32 | - \f$ n*c x_i \f$ input signal |
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33 | - \f$ n*c y_i \f$ output signal |
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34 | |
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35 | For convenience, the samplerate of the input signal is also stored in the |
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36 | object. |
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37 | |
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38 | Feedforward and feedback parameters can be modified using |
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39 | aubio_filter_get_feedback() and aubio_filter_get_feedforward(). |
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40 | |
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41 | The function aubio_filter_do_outplace() computes the following output signal |
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42 | \f$ y[n] \f$ from the input signal \f$ x[n] \f$: |
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43 | |
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44 | \f{eqnarray*}{ |
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45 | y[n] = b_0 x[n] & + & b_1 x[n-1] + b_2 x[n-2] + ... + b_P x[n-P] \\ |
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46 | & - & a_1 y[n-1] - a_2 y[n-2] - ... - a_P y[n-P] \\ |
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47 | \f} |
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48 | |
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49 | The function aubio_filter_do() executes the same computation but modifies |
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50 | directly the input signal (in-place). |
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51 | |
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52 | The function aubio_filter_do_filtfilt() version runs the filter twice, first |
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53 | forward then backward, to compensate with the phase shifting of the forward |
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54 | operation. |
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55 | |
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56 | Some convenience functions are provided: |
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57 | - new_aubio_filter_a_weighting() and aubio_filter_set_a_weighting(), |
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58 | - new_aubio_filter_c_weighting() and aubio_filter_set_c_weighting(). |
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59 | |
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60 | */ |
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61 | |
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62 | #ifdef __cplusplus |
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63 | extern "C" { |
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64 | #endif |
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65 | |
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66 | /** Digital filter |
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67 | |
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68 | */ |
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69 | typedef struct _aubio_filter_t aubio_filter_t; |
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70 | |
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71 | /** filter input vector (in-place) |
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72 | |
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73 | \param f filter object as returned by new_aubio_filter() |
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74 | \param in input vector to filter |
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75 | |
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76 | */ |
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77 | void aubio_filter_do (aubio_filter_t * f, fvec_t * in); |
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78 | |
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79 | /** filter input vector (out-of-place) |
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80 | |
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81 | \param f filter object as returned by new_aubio_filter() |
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82 | \param in input vector to filter |
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83 | \param out output vector to store filtered input |
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84 | |
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85 | */ |
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86 | void aubio_filter_do_outplace (aubio_filter_t * f, fvec_t * in, fvec_t * out); |
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87 | |
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88 | /** filter input vector forward and backward |
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89 | |
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90 | \param f ::aubio_filter_t object as returned by new_aubio_filter() |
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91 | \param in ::fvec_t input vector to filter |
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92 | \param tmp memory space to use for computation |
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93 | |
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94 | */ |
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95 | void aubio_filter_do_filtfilt (aubio_filter_t * f, fvec_t * in, fvec_t * tmp); |
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96 | |
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97 | /** returns a pointer to feedback coefficients \f$ a_i \f$ |
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98 | |
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99 | \param f filter object to get parameters from |
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100 | |
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101 | \return a pointer to the \f$ a_0 ... a_i ... a_P \f$ coefficients |
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102 | |
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103 | */ |
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104 | lvec_t *aubio_filter_get_feedback (aubio_filter_t * f); |
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105 | |
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106 | /** returns a pointer to feedforward coefficients \f$ b_i \f$ |
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107 | |
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108 | \param f filter object to get coefficients from |
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109 | |
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110 | \return a pointer to the \f$ b_0 ... b_i ... b_P \f$ coefficients |
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111 | |
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112 | */ |
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113 | lvec_t *aubio_filter_get_feedforward (aubio_filter_t * f); |
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114 | |
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115 | /** get order of the filter |
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116 | |
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117 | \param f filter to get order from |
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118 | |
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119 | \return the order of the filter |
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120 | |
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121 | */ |
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122 | uint_t aubio_filter_get_order (aubio_filter_t * f); |
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123 | |
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124 | /** get sampling rate of the filter |
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125 | |
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126 | \param f filter to get sampling rate from |
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127 | |
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128 | \return the sampling rate of the filter, in Hz |
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129 | |
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130 | */ |
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131 | uint_t aubio_filter_get_samplerate (aubio_filter_t * f); |
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132 | |
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133 | /** get sampling rate of the filter |
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134 | |
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135 | \param f filter to get sampling rate from |
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136 | \param samplerate sample rate to set the filter to |
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137 | |
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138 | \return the sampling rate of the filter, in Hz |
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139 | |
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140 | */ |
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141 | uint_t aubio_filter_set_samplerate (aubio_filter_t * f, uint_t samplerate); |
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142 | |
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143 | /** create new filter object |
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144 | |
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145 | This function creates a new ::aubio_filter_t object, given an order |
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146 | and a specific number of channels. |
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147 | |
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148 | \param samplerate signal sampling rate |
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149 | \param order order of the filter (number of coefficients) |
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150 | \param channels number of channels to allocate |
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151 | |
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152 | \return the newly created filter object |
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153 | |
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154 | */ |
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155 | aubio_filter_t *new_aubio_filter (uint_t order, uint_t channels); |
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156 | |
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157 | /** delete a filter object |
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158 | |
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159 | \param f filter object to delete |
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160 | |
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161 | */ |
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162 | void del_aubio_filter (aubio_filter_t * f); |
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163 | |
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164 | #ifdef __cplusplus |
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165 | } |
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166 | #endif |
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167 | |
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168 | #endif /*FILTER_H*/ |
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