sfFDN::AllpassFilter Class Reference

Implements a simple allpass filter with differential equation \(y(n) = g*x(n) + x(n-1) -g*y(n-1)\). More...

#include <filter.h>

Inheritance diagram for sfFDN::AllpassFilter:

Collaboration diagram for sfFDN::AllpassFilter:

Public Member Functions
	AllpassFilter (const AllpassFilterOptions &config={})
	Constructs an allpass filter.
void	SetCoefficients (float coeff) noexcept SFFDN_NONBLOCKING
	Sets the allpass coefficient.
void	WarpState (float last_in, float coeff) noexcept SFFDN_NONBLOCKING
	Re-seeds the filter state and sets a new coefficient in one step.
float	Tick (float in) noexcept SFFDN_NONBLOCKING
	Input a sample in the filter and return the next output.
void	Process (const AudioBuffer &input, AudioBuffer &output) noexcept SFFDN_NONBLOCKING override
	Processes a block of input samples through the filter.
uint32_t	InputChannelCount () const noexcept SFFDN_NONBLOCKING override
	Returns the number of input channels supported by this processor.
uint32_t	OutputChannelCount () const noexcept SFFDN_NONBLOCKING override
	Returns the number of output channels produced by this processor.
void	Clear () override
	Clears the internal state of the processor.
std::unique_ptr< AudioProcessor >	Clone () const override
	Creates a copy of the filter.
Public Member Functions inherited from sfFDN::AudioProcessor

Additional Inherited Members
Protected Member Functions inherited from sfFDN::AudioProcessor
	AudioProcessor (const AudioProcessor &)=default
AudioProcessor &	operator= (const AudioProcessor &)=default
	AudioProcessor (AudioProcessor &&) noexcept=default
AudioProcessor &	operator= (AudioProcessor &&) noexcept=default

Detailed Description

Implements a simple allpass filter with differential equation \(y(n) = g*x(n) + x(n-1) -g*y(n-1)\).

Member Function Documentation

Clear()

void sfFDN::AllpassFilter::Clear ( )

overridevirtual

Clears the internal state of the processor.

This function resets the internal state of the filter to zero.

Implements sfFDN::AudioProcessor.

Clone()

std::unique_ptr< AudioProcessor > sfFDN::AllpassFilter::Clone ( ) const

overridevirtual

Creates a copy of the filter.

Returns

A unique pointer to the cloned filter.

Implements sfFDN::AudioProcessor.

InputChannelCount()

uint32_t sfFDN::AllpassFilter::InputChannelCount ( ) const

overridevirtualnoexcept

Returns the number of input channels supported by this processor.

Returns

The number of input channels.

Implements sfFDN::AudioProcessor.

OutputChannelCount()

uint32_t sfFDN::AllpassFilter::OutputChannelCount ( ) const

overridevirtualnoexcept

Returns the number of output channels produced by this processor.

Returns

The number of output channels.

Implements sfFDN::AudioProcessor.

Process()

void sfFDN::AllpassFilter::Process ( const AudioBuffer & input, AudioBuffer & output )

overridevirtualnoexcept

Processes a block of input samples through the filter.

Parameters

input	The input audio buffer.
output	The output audio buffer. The input and output buffers must have the same number of channels and sample count.

Implements sfFDN::AudioProcessor.

SetCoefficients()

void sfFDN::AllpassFilter::SetCoefficients ( float coeff )

inlinenoexcept

Sets the allpass coefficient.

Parameters

coeff

The allpass coefficient.

Tick()

float sfFDN::AllpassFilter::Tick ( float in )

noexcept

Input a sample in the filter and return the next output.

Parameters

in	The input sample

Returns

The next output sample

WarpState()

void sfFDN::AllpassFilter::WarpState ( float last_in, float coeff )

inlinenoexcept

Re-seeds the filter state and sets a new coefficient in one step.

The filter is a Direct Form I first order allpass, so its state is the previous input sample and the previous output sample. When the filter is used as a fractional delay and the signal feeding it is switched to a different tap of a delay line, the stored previous input belongs to the old tap and is no longer the sample that precedes the next input. Feeding that stale sample back into Tick() injects a step into the output; this is the source of the clicks heard when an allpass interpolated delay line crosses an integer sample boundary.

Parameters

last_in	The sample that precedes the next input, i.e. the previous output of the new tap.
coeff	The new allpass coefficient.

Note

The previous output is deliberately left untouched: it is a genuine continuation of the output signal, and the remaining discontinuity decays at a rate set by the coefficient.

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

• include/sffdn/filter.h