/***************************************************/ /*! \class TwoPole \brief STK two-pole filter class. This class implements a two-pole digital filter. A method is provided for creating a resonance in the frequency response while maintaining a nearly constant filter gain. by Perry R. Cook and Gary P. Scavone, 1995--2017. */ /***************************************************/ #include "TwoPole.h" #include namespace stk { TwoPole :: TwoPole( void ) { b_.resize( 1 ); a_.resize( 3 ); inputs_.resize( 1, 1, 0.0 ); outputs_.resize( 3, 1, 0.0 ); b_[0] = 1.0; a_[0] = 1.0; Stk::addSampleRateAlert( this ); } TwoPole :: ~TwoPole() { Stk::removeSampleRateAlert( this ); } void TwoPole :: sampleRateChanged( StkFloat newRate, StkFloat oldRate ) { if ( !ignoreSampleRateChange_ ) { oStream_ << "TwoPole::sampleRateChanged: you may need to recompute filter coefficients!"; handleError( StkError::WARNING ); } } void TwoPole :: setResonance( StkFloat frequency, StkFloat radius, bool normalize ) { #if defined(_STK_DEBUG_) if ( frequency < 0.0 || frequency > 0.5 * Stk::sampleRate() ) { oStream_ << "TwoPole::setResonance: frequency argument (" << frequency << ") is out of range!"; handleError( StkError::WARNING ); return; } if ( radius < 0.0 || radius >= 1.0 ) { oStream_ << "TwoPole::setResonance: radius argument (" << radius << ") is out of range!"; handleError( StkError::WARNING ); return; } #endif a_[2] = radius * radius; a_[1] = (StkFloat) -2.0 * radius * cos(TWO_PI * frequency / Stk::sampleRate()); if ( normalize ) { // Normalize the filter gain ... not terribly efficient. StkFloat real = 1 - radius + (a_[2] - radius) * cos(TWO_PI * 2 * frequency / Stk::sampleRate()); StkFloat imag = (a_[2] - radius) * sin(TWO_PI * 2 * frequency / Stk::sampleRate()); b_[0] = sqrt( pow(real, 2) + pow(imag, 2) ); } } void TwoPole :: setCoefficients( StkFloat b0, StkFloat a1, StkFloat a2, bool clearState ) { b_[0] = b0; a_[1] = a1; a_[2] = a2; if ( clearState ) this->clear(); } } // stk namespace