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149 lines
4.4 KiB
149 lines
4.4 KiB
/* |
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This program is free software: you can redistribute it and/or modify |
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it under the terms of the GNU General Public License as published by |
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the Free Software Foundation, either version 3 of the License, or |
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(at your option) any later version. |
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This program is distributed in the hope that it will be useful, |
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but WITHOUT ANY WARRANTY; without even the implied warranty of |
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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GNU General Public License for more details. |
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You should have received a copy of the GNU General Public License |
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along with this program. If not, see <http://www.gnu.org/licenses/>. |
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*/ |
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#include "NotchFilter.h" |
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/* |
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calculate the attenuation and quality factors of the filter |
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*/ |
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template <class T> |
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void NotchFilter<T>::calculate_A_and_Q(float center_freq_hz, float bandwidth_hz, float attenuation_dB, float& A, float& Q) { |
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A = powf(10, -attenuation_dB / 40.0f); |
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if (center_freq_hz > 0.5 * bandwidth_hz) { |
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const float octaves = log2f(center_freq_hz / (center_freq_hz - bandwidth_hz / 2.0f)) * 2.0f; |
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Q = sqrtf(powf(2, octaves)) / (powf(2, octaves) - 1.0f); |
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} else { |
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Q = 0.0; |
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} |
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} |
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/* |
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initialise filter |
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*/ |
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template <class T> |
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void NotchFilter<T>::init(float sample_freq_hz, float center_freq_hz, float bandwidth_hz, float attenuation_dB) |
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{ |
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// check center frequency is in the allowable range |
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if ((center_freq_hz > 0.5 * bandwidth_hz) && (center_freq_hz < 0.5 * sample_freq_hz)) { |
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float A, Q; |
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calculate_A_and_Q(center_freq_hz, bandwidth_hz, attenuation_dB, A, Q); |
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init_with_A_and_Q(sample_freq_hz, center_freq_hz, A, Q); |
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} else { |
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initialised = false; |
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} |
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} |
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template <class T> |
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void NotchFilter<T>::init_with_A_and_Q(float sample_freq_hz, float center_freq_hz, float A, float Q) |
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{ |
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if ((center_freq_hz > 0.0) && (center_freq_hz < 0.5 * sample_freq_hz) && (Q > 0.0)) { |
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float omega = 2.0 * M_PI * center_freq_hz / sample_freq_hz; |
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float alpha = sinf(omega) / (2 * Q); |
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b0 = 1.0 + alpha*sq(A); |
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b1 = -2.0 * cosf(omega); |
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b2 = 1.0 - alpha*sq(A); |
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a0_inv = 1.0/(1.0 + alpha); |
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a1 = b1; |
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a2 = 1.0 - alpha; |
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initialised = true; |
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} else { |
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initialised = false; |
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} |
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} |
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/* |
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apply a new input sample, returning new output |
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*/ |
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template <class T> |
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T NotchFilter<T>::apply(const T &sample) |
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{ |
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if (!initialised) { |
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// if we have not been initialised when return the input |
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// sample as output and update delayed samples |
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ntchsig2 = ntchsig1; |
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ntchsig1 = ntchsig; |
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ntchsig = sample; |
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signal2 = signal1; |
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signal1 = sample; |
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return sample; |
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} |
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ntchsig2 = ntchsig1; |
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ntchsig1 = ntchsig; |
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ntchsig = sample; |
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T output = (ntchsig*b0 + ntchsig1*b1 + ntchsig2*b2 - signal1*a1 - signal2*a2) * a0_inv; |
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signal2 = signal1; |
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signal1 = output; |
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return output; |
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} |
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template <class T> |
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void NotchFilter<T>::reset() |
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{ |
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ntchsig2 = ntchsig1 = T(); |
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signal2 = signal1 = T(); |
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} |
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// table of user settable parameters |
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const AP_Param::GroupInfo NotchFilterParams::var_info[] = { |
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// @Param: ENABLE |
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// @DisplayName: Enable |
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// @Description: Enable notch filter |
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// @Values: 0:Disabled,1:Enabled |
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// @User: Advanced |
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AP_GROUPINFO_FLAGS("ENABLE", 1, NotchFilterParams, _enable, 0, AP_PARAM_FLAG_ENABLE), |
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// Slots 2 and 3 are reserved - they were integer versions of FREQ and BW which have since been converted to float |
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// @Param: ATT |
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// @DisplayName: Attenuation |
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// @Description: Notch attenuation in dB |
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// @Range: 5 30 |
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// @Units: dB |
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// @User: Advanced |
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AP_GROUPINFO("ATT", 4, NotchFilterParams, _attenuation_dB, 15), |
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// @Param: FREQ |
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// @DisplayName: Frequency |
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// @Description: Notch center frequency in Hz |
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// @Range: 10 400 |
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// @Units: Hz |
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// @User: Advanced |
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AP_GROUPINFO("FREQ", 5, NotchFilterParams, _center_freq_hz, 80), |
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// @Param: BW |
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// @DisplayName: Bandwidth |
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// @Description: Notch bandwidth in Hz |
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// @Range: 5 100 |
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// @Units: Hz |
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// @User: Advanced |
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AP_GROUPINFO("BW", 6, NotchFilterParams, _bandwidth_hz, 20), |
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AP_GROUPEND |
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}; |
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/* |
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a notch filter with enable and filter parameters - constructor |
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*/ |
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NotchFilterParams::NotchFilterParams(void) |
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{ |
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AP_Param::setup_object_defaults(this, var_info); |
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} |
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/* |
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instantiate template classes |
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*/ |
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template class NotchFilter<float>; |
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template class NotchFilter<Vector3f>;
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