LowShelfFilter< T > Class Template Reference

Second-order low-shelf filter (BiQuad DF2). Boosts or cuts frequencies below the shelf frequency by the specified gain (in dB) while leaving higher frequencies unchanged. Commonly used in tone controls and equalization. Coefficients are derived from the Audio EQ Cookbook. More...

#include <Filter.h>

Inheritance diagram for LowShelfFilter< T >:

Public Member Functions
	LowShelfFilter ()=default
	LowShelfFilter (float frequency, float sampleRate, float gain, float slope=1.0f)
void	begin (float frequency, float sampleRate, float gain, float slope=1.0f)
T	process (T value) override
	Processes the input value and returns the filtered output value.
void	reset () override

Protected Attributes
T	a_1 = 0
T	a_2 = 0
T	b_0 = 0
T	b_1 = 0
T	b_2 = 0
T	w_0 = 0
T	w_1 = 0

Detailed Description

template<typename T = float>
class audio_tools::LowShelfFilter< T >

Second-order low-shelf filter (BiQuad DF2). Boosts or cuts frequencies below the shelf frequency by the specified gain (in dB) while leaving higher frequencies unchanged. Commonly used in tone controls and equalization. Coefficients are derived from the Audio EQ Cookbook.

Parameters

frequency	shelf transition frequency in Hz
sampleRate	sample rate in Hz
gain	boost/cut in dB (positive = boost, negative = cut)
slope	shelf slope (default 1.0; values < 1.0 give a gentler slope)

Author

pschatzmann

Copyright

GNU General Public License v3.0

Template Parameters

T

sample type (use float or double). NOTE: unlike the other filters here, LowShelfFilterDF1 is NOT a reliable fix for bounded fixed-point types like q1_14_t: shelf coefficients scale with the linear gain factor 10^(gain_dB/40) and can exceed a bounded type's range even at modest gain settings, independent of DF1 vs DF2 – this is a coefficient headroom limitation, not the DF2 state-headroom issue DF1 solves for the other filter types. begin() logs an error (LOGE) via checkCoeffRange() if this happens; check for that warning rather than assuming it works.

Constructor & Destructor Documentation

LowShelfFilter() [1/2]

template<typename T = float>

LowShelfFilter ( )

default

LowShelfFilter() [2/2]

template<typename T = float>

LowShelfFilter ( float  frequency, float  sampleRate, float  gain, float  slope = 1.0f  )

inline

Member Function Documentation

begin()

template<typename T = float>

void begin ( float  frequency, float  sampleRate, float  gain, float  slope = 1.0f  )

inline

process()

template<typename T = float>

T process ( T  in )

inlineoverridevirtualinherited

Processes the input value and returns the filtered output value.

Implements Filter< T >.

reset()

template<typename T = float>

void reset ( )

inlineoverridevirtualinherited

Clears the internal state (delay lines) without changing the coefficients. Call after reconfiguring filter parameters via begin() to avoid transients from stale state.

Reimplemented from Filter< T >.

Member Data Documentation

a_1

template<typename T = float>

T a_1 = 0

protectedinherited

a_2

template<typename T = float>

T a_2 = 0

protectedinherited

b_0

template<typename T = float>

T b_0 = 0

protectedinherited

b_1

template<typename T = float>

T b_1 = 0

protectedinherited

b_2

template<typename T = float>

T b_2 = 0

protectedinherited

w_0

template<typename T = float>

T w_0 = 0

protectedinherited

w_1

template<typename T = float>

T w_1 = 0

protectedinherited

---

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

• src/AudioTools/CoreAudio/AudioFilter/Filter.h