135 lines
4.0 KiB
C++
135 lines
4.0 KiB
C++
/*
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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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const float octaves = log2f(center_freq_hz / (center_freq_hz - bandwidth_hz / 2.0f)) * 2.0f;
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A = powf(10, -attenuation_dB / 40.0f);
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Q = sqrtf(powf(2, octaves)) / (powf(2, octaves) - 1.0f);
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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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// adjust the center frequency to be in the allowable range
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center_freq_hz = constrain_float(center_freq_hz, bandwidth_hz * 0.52f, sample_freq_hz * 0.48f);
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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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}
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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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float omega = 2.0 * M_PI * center_freq_hz / sample_freq_hz;
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float alpha = sinf(omega) / (2 * Q/A);
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b0 = 1.0 + alpha*A;
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b1 = -2.0 * cosf(omega);
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b2 = 1.0 - alpha*A;
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a0_inv = 1.0/(1.0 + alpha/A);
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a1 = -2.0 * cosf(omega);
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a2 = 1.0 - alpha/A;
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initialised = true;
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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
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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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