#ifndef BIQUADFILTERGATE_H #define BIQUADFILTERGATE_H /** lower frequency limit. about 20 Hz at 48.000 Hz */ #define BFG_MIN 0.0005 #define BFG_MAX 0.4995 using Frequency = float; using Amplitude = float; using SampleRate = int; #include #include #define K_PI M_PI /** * a simple biquad filter that can be used * for low- or high-pass filtering * * http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt */ template class BiquadFilterGate { public: /** ctor */ BiquadFilterGate() : in(), out(), disabled(false) { reset(); } /** filter the given amplitude of the given channel (history) */ Amplitude filter( const unsigned int ch, const Amplitude aIn ) { Amplitude aOut = 0; aOut += aIn *(b0a0); aOut += in[ch][0] *(b1a0); aOut += in[ch][1] *(b2a0); aOut -= out[ch][0]*(a1a0); aOut -= out[ch][1]*(a2a0); //aOut = clamp1(aOut); in[ch][1] = in[ch][0]; in[ch][0] = aIn; out[ch][1] = out[ch][0]; out[ch][0] = aOut; return aOut; } /** reset (disable) the filter */ void reset() { b0a0 = 1.0; b1a0 = 0.0; b2a0 = 0.0; a1a0 = 0.0; a2a0 = 0.0; memset(in, 0, sizeof(in)); memset(out, 0, sizeof(out)); } /** configure the filter as low-pass. freqFact between ]0;0.5[ */ void setLowPass( double freqFact, const float octaves ) { if (freqFact < BFG_MIN) {freqFact = BFG_MIN;} if (freqFact > BFG_MAX) {disabled = true; return;} disabled = false; double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = (1.0 - cos(w0))/2.0; double b1 = 1.0 - cos(w0); double b2 = (1.0 - cos(w0))/2.0; double a0 = 1.0 + alpha; double a1 = -2.0*cos(w0); double a2 = 1.0 - alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as low-pass */ void setLowPass( const Frequency freq, const float octaves, const SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setLowPass(freqFact, octaves); } //http://dspwiki.com/index.php?title=Lowpass_Resonant_Biquad_Filter //http://www.opensource.apple.com/source/WebCore/WebCore-7536.26.14/platform/audio/Biquad.cpp /** * configure as low-pass filter with resonance * @param freqFact the frequency factor between ]0;0.5[ * @param res */ void setLowPassResonance( double freqFact, float res ) { if (freqFact < BFG_MIN) {freqFact = BFG_MIN;} if (freqFact > BFG_MAX) {disabled = true; return;} disabled = false; res *= 10; double g = pow(10.0, 0.05 * res); double d = sqrt((4 - sqrt(16 - 16 / (g * g))) / 2); double theta = K_PI * freqFact; double sn = 0.5 * d * sin(theta); double beta = 0.5 * (1 - sn) / (1 + sn); double gamma = (0.5 + beta) * cos(theta); double alpha = 0.25 * (0.5 + beta - gamma); double a0 = 1.0; double b0 = 2.0 * alpha; double b1 = 2.0 * 2.0 * alpha; double b2 = 2.0 * alpha; double a1 = 2.0 * -gamma; double a2 = 2.0 * beta; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as high-pass. freqFact between ]0;0.5[ */ void setHighPass( double freqFact, const float octaves ) { if (freqFact < BFG_MIN) {disabled = true; return;} if (freqFact > BFG_MAX) {freqFact = BFG_MAX;} disabled = false; double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = (1.0 + cos(w0))/2.0; double b1 = -(1.0 + cos(w0)); double b2 = (1.0 + cos(w0))/2.0; double a0 = 1.0 + alpha; double a1 = -2.0*cos(w0); double a2 = 1.0 - alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as high-pass */ void setHighPass( const Frequency freq, const float octaves, const SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setHighPass(freqFact, octaves); } /** configure the filter as band-pass. freqFact between ]0;0.5[ */ void setBandPass( double freqFact, const float octaves ) { if (freqFact < BFG_MIN) {disabled = true; return;} if (freqFact > BFG_MAX) {disabled = true; return;} disabled = false; //double w0 = 2 * K_PI * / 2 / freqFact; double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = sin(w0)/2.0; double b1 = 0.0; double b2 = -sin(w0)/2.0; double a0 = 1.0 + alpha; double a1 = -2.0*cos(w0); double a2 = 1.0 - alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as band-pass */ void setBandPass( const Frequency freq, const float octaves, SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setBandPass(freqFact, octaves); } /** configure the filter as all-pass. freqFact between ]0;0.5[ */ void setAllPass( double freqFact, const float octaves ) { double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = 1 - alpha; double b1 = -2*cos(w0); double b2 = 1 + alpha; double a0 = 1 + alpha; double a1 = -2*cos(w0); double a2 = 1 - alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as all-pass */ void setAllPass( const Frequency freq, const float octaves, const SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setAllPass(freqFact, octaves); } /** configure as notch filter. freqFact between ]0;0.5[ */ void setNotch( double freqFact, const float octaves ) { double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = 1.0; double b1 = -2.0*cos(w0); double b2 = 1.0; double a0 = 1.0 + alpha; double a1 = -2.0*cos(w0); double a2 = 1.0 - alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure as notch filter */ void setNotch( const Frequency freq, const float octaves, const SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setNotch(freqFact, octaves); } /** configure the filter as low-shelf. increase all aplitudes below freq? freqFact between ]0;0.5[ */ void setLowShelf( double freqFact, const float octaves, const float gain ) { double A = sqrt( pow(10, (gain/20.0)) ); double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = A*( (A+1.0) - (A-1.0)*cos(w0) + 2.0*sqrt(A)*alpha ); double b1 = 2.0*A*( (A-1.0) - (A+1.0)*cos(w0) ); double b2 = A*( (A+1.0) - (A-1.0)*cos(w0) - 2.0*sqrt(A)*alpha ); double a0 = (A+1.0) + (A-1.0)*cos(w0) + 2.0*sqrt(A)*alpha; double a1 = -2.0*( (A-1.0) + (A+1.0)*cos(w0) ); double a2 = (A+1.0) + (A-1.0)*cos(w0) - 2.0*sqrt(A)*alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as low-shelf. increase all aplitudes below freq? */ void setLowShelf( const Frequency freq, const float octaves, const float gain, const SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setLowShelf(freqFact, octaves, gain); } /** configure the filter as high-shelf. increase all amplitues above freq? freqFact between ]0;0.5[ */ void setHighShelf( double freqFact, const float octaves, const float gain ) { double A = sqrt( pow(10, (gain/20.0)) ); double w0 = 2.0 * K_PI * freqFact; double alpha = sin(w0)*sinh( log(2)/2 * octaves * w0/sin(w0) ); double b0 = A*( (A+1.0) + (A-1.0)*cos(w0) + 2.0*sqrt(A)*alpha ); double b1 = -2.0*A*( (A-1.0) + (A+1.0)*cos(w0) ); double b2 = A*( (A+1.0) + (A-1.0)*cos(w0) - 2.0*sqrt(A)*alpha ); double a0 = (A+1.0) - (A-1.0)*cos(w0) + 2.0*sqrt(A)*alpha; double a1 = 2.0*( (A-1.0) - (A+1.0)*cos(w0) ); double a2 = (A+1.0) - (A-1.0)*cos(w0) - 2.0*sqrt(A)*alpha; setValues(a0, a1, a2, b0, b1, b2); } /** configure the filter as high-shelf. increase all amplitues above freq? */ void setHighShelf( const Frequency freq, const float octaves, const float gain, const SampleRate sRate ) { double freqFact = double(freq) / double(sRate); setHighShelf(freqFact, octaves, gain); } protected: /** pre-calculate the quotients for the filtering */ void setValues(double a0, double a1, double a2, double b0, double b1, double b2) { b0a0 = float(b0/a0); b1a0 = float(b1/a0); b2a0 = float(b2/a0); a2a0 = float(a2/a0); a1a0 = float(a1/a0); } /** the bi-quad filter params */ float b0a0; float b1a0; float b2a0; float a1a0; float a2a0; /** history for input values, per channel */ Amplitude in[channels][2]; /** history for ouput values, per channel */ Amplitude out[channels][2]; /** filter disabled due to wrong params? */ bool disabled; }; #endif // BIQUADFILTERGATE_H