pulp::signal::TptFilterT< SampleType > Class Template Reference

First-order TPT (trapezoidal integration) filter. More...

#include <tpt_filter.hpp>

Classes
struct	Outputs
	Process and return all three outputs at once. More...

Public Member Functions
	TptFilterT ()=default
void	prepare (SampleType sample_rate)
void	set_cutoff (SampleType hz)
	Set cutoff frequency in Hz. Safe to modulate per-sample.
SampleType	cutoff () const
SampleType	sample_rate () const
SampleType	process_lowpass (SampleType input)
	Process and return the lowpass output.
SampleType	process_highpass (SampleType input)
	Process and return the highpass output.
SampleType	process_allpass (SampleType input)
	Process and return the allpass output.
void	process_lowpass (SampleType *buffer, std::size_t num_samples)
	Process a buffer in place, replacing it with the lowpass output.
void	process_highpass (SampleType *buffer, std::size_t num_samples)
	Process a buffer in place, replacing it with the highpass output.
void	process_allpass (SampleType *buffer, std::size_t num_samples)
	Process a buffer in place, replacing it with the allpass output.
Outputs	process (SampleType input)
void	reset ()

Static Public Attributes
static constexpr SampleType	kMinCutoffHz = SampleType{1}
static constexpr SampleType	kMaxCutoffFraction = SampleType{0.49}
static constexpr SampleType	kMinSampleRate = SampleType{4}
	Conservative defensive floor that leaves a non-empty valid cutoff interval above the 1 Hz lower bound.

Detailed Description

template<typename SampleType = float>
class pulp::signal::TptFilterT< SampleType >

First-order TPT (trapezoidal integration) filter.

Provides lowpass, highpass, and allpass outputs simultaneously. The TPT structure is unconditionally stable under modulation, making it ideal for filter FM and fast cutoff sweeps.

RT contract: prepare(), cutoff modulation, process paths, queries, and reset are fixed-state only and allocate no memory.

TptFilter filt;
filt.prepare(44100.0f);
filt.set_cutoff(1000.0f);
float lp = filt.process_lowpass(input);

Constructor & Destructor Documentation

TptFilterT()

template<typename SampleType = float>

pulp::signal::TptFilterT< SampleType >::TptFilterT ( )

default

Member Function Documentation

cutoff()

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::cutoff ( ) const

inline

prepare()

template<typename SampleType = float>

void pulp::signal::TptFilterT< SampleType >::prepare ( SampleType sample_rate )

inline

process()

template<typename SampleType = float>

Outputs pulp::signal::TptFilterT< SampleType >::process ( SampleType input )

inline

process_allpass() [1/2]

template<typename SampleType = float>

void pulp::signal::TptFilterT< SampleType >::process_allpass ( SampleType * buffer, std::size_t num_samples )

inline

Process a buffer in place, replacing it with the allpass output.

process_allpass() [2/2]

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::process_allpass ( SampleType input )

inline

Process and return the allpass output.

process_highpass() [1/2]

template<typename SampleType = float>

void pulp::signal::TptFilterT< SampleType >::process_highpass ( SampleType * buffer, std::size_t num_samples )

inline

Process a buffer in place, replacing it with the highpass output.

process_highpass() [2/2]

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::process_highpass ( SampleType input )

inline

Process and return the highpass output.

process_lowpass() [1/2]

template<typename SampleType = float>

void pulp::signal::TptFilterT< SampleType >::process_lowpass ( SampleType * buffer, std::size_t num_samples )

inline

Process a buffer in place, replacing it with the lowpass output.

Same arithmetic as the per-sample path on a register-resident state. The denormal snap runs once per kSnapChunkSamples chunk (snap_chunks()). The integrator's pole is 1 - 2g; unless |1 - 2g| < 0.44 (cutoffs near a quarter of the sample rate) a state at or above 1e-15 at the start of a chunk cannot decay into the float subnormal range before the next snap, and inside that band the tail falls through the subnormal range; there, and with subnormal input, the state can stay subnormal until the next snap, so residency is bounded by one chunk.

process_lowpass() [2/2]

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::process_lowpass ( SampleType input )

inline

Process and return the lowpass output.

The state update is written as s + 2g * (input - s) (algebraically lp + v) so the recursion is one subtract and one multiply-add; the lowpass output is formed off that path.

reset()

template<typename SampleType = float>

void pulp::signal::TptFilterT< SampleType >::reset ( )

inline

sample_rate()

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::sample_rate ( ) const

inline

set_cutoff()

template<typename SampleType = float>

void pulp::signal::TptFilterT< SampleType >::set_cutoff ( SampleType hz )

inline

Set cutoff frequency in Hz. Safe to modulate per-sample.

Member Data Documentation

kMaxCutoffFraction

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::kMaxCutoffFraction = SampleType{0.49}

staticconstexpr

kMinCutoffHz

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::kMinCutoffHz = SampleType{1}

staticconstexpr

kMinSampleRate

template<typename SampleType = float>

SampleType pulp::signal::TptFilterT< SampleType >::kMinSampleRate = SampleType{4}

staticconstexpr

Conservative defensive floor that leaves a non-empty valid cutoff interval above the 1 Hz lower bound.

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

• /home/runner/work/pulp/pulp/core/signal/include/pulp/signal/tpt_filter.hpp