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# stk::Filter Class Reference

STK abstract filter class. More...

`#include <Filter.h>`

Inheritance diagram for stk::Filter:

List of all members.

## Public Member Functions
| Filter (void)
| Class constructor.
unsigned int | channelsIn (void) const
| Return the number of input channels for the class.
unsigned int | channelsOut (void) const
| Return the number of output channels for the class.
virtual void | clear (void)
| Clears all internal states of the filter.
void | setGain (StkFloat gain)
| Set the filter gain.
StkFloat | getGain (void) const
| Return the current filter gain.
StkFloat | phaseDelay (StkFloat frequency)
| Return the filter phase delay at the specified frequency.
const StkFrames & | lastFrame (void) const
| Return an StkFrames reference to the last output sample frame.
virtual StkFrames & | tick (StkFrames &frames, unsigned int channel=0)=0
| Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.

## Detailed Description

STK abstract filter class.

This class provides limited common functionality for STK digital filter subclasses. It is general enough to support both monophonic and polyphonic input/output classes.

by Perry R. Cook and Gary P. Scavone, 1995-2012.

## Member Function Documentation

void stk::Filter::setGain | ( | StkFloat | gain | ) | `[inline]`

Set the filter gain.

The gain is applied at the filter input and does not affect the coefficient values. The default gain value is 1.0.

    00042 { gain_ = gain; };

StkFloat stk::Filter::phaseDelay | ( | StkFloat | frequency | ) | `[inline]`

Return the filter phase delay at the specified frequency.

Note that the phase delay calculation accounts for the filter gain. The frequency value should be greater than 0.0 and less than or equal to one-half the sample rate.

    00094 {
    00095   if ( frequency <= 0.0 || frequency > 0.5 * Stk::sampleRate() ) {
    00096     oStream_ << "Filter::phaseDelay: argument (" << frequency << ") is out of range!";
    00097     handleError( StkError::WARNING ); return 0.0;
    00098   }
    00099
    00100   StkFloat omegaT = 2 * PI * frequency / Stk::sampleRate();
    00101   StkFloat real = 0.0, imag = 0.0;
    00102   for ( unsigned int i=0; i<b_.size(); i++ ) {
    00103     real += b_[i] * std::cos( i * omegaT );
    00104     imag -= b_[i] * std::sin( i * omegaT );
    00105   }
    00106   real *= gain_;
    00107   imag *= gain_;
    00108
    00109   StkFloat phase = atan2( imag, real );
    00110
    00111   real = 0.0, imag = 0.0;
    00112   for ( unsigned int i=0; i<a_.size(); i++ ) {
    00113     real += a_[i] * std::cos( i * omegaT );
    00114     imag -= a_[i] * std::sin( i * omegaT );
    00115   }
    00116
    00117   phase -= std::atan2( imag, real );
    00118   phase = std::fmod( -phase, 2 * PI );
    00119   return phase / omegaT;
    00120 }

virtual StkFrames& stk::Filter::tick | ( | StkFrames & | frames,
|  | unsigned int | channel = `0` |
| ) |  |  | `[pure virtual]`

Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.

The StkFrames argument reference is returned. The `channel` argument must be less than the number of channels in the StkFrames argument (the first channel is specified by 0). However, range checking is only performed if _STK_DEBUG_ is defined during compilation, in which case an out-of-range value will trigger an StkError exception.

Implemented in stk::BiQuad, stk::Delay, stk::DelayA, stk::DelayL, stk::Fir, stk::FormSwep, stk::Iir, stk::OnePole, stk::OneZero, stk::PoleZero, stk::TapDelay, stk::TwoPole, and stk::TwoZero.

The documentation for this class was generated from the following file:

- Filter.h

The Synthesis ToolKit in C++ (STK)
©1995-2012 Perry R. Cook and Gary P. Scavone. All Rights Reserved.