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Overview

Cascade of second order filters. High precision implementation

Discussion

This module implements a general purpose second order cascaded filter that is capable of realizing many different filter types. The module performs internal smoothing allowing the filters to be updated without introducing clicks. In all cases, the module implements an underlying second order filter. First order filters are realized by setting some of the second order coefficients to zero.

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filterType=22, 2nd order Butterworth high pass filter with variable Q. [freq, Q].

Type Definition

Code Block
typedef struct _ModuleSOFCascadeHPFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 numStages;                              // Number of cascaded stages of the second order filter.
    FLOAT32 smoothingTime;                        // Time constant of the smoothing process
    INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0)
    fract32 smoothingCoeff;                       // Smoothing coefficient. This is computed based on the smoothingTime, sample rate, and block size of the module
    INT32 bShift;                                 // Number of bits to shift of Numerator coefficients
    INT32 aShift;                                 // Number of bits to shift of Denominator coefficients
    INT32* filterType;                            // Selects the type of filter that is implemented by the module: Bypass=0, Gain=1, Butter1stLPF=2, Butter2ndLPF=3, Butter1stHPF=4, Butter2ndHPF=5, Allpass1st=6, Allpass2nd=7, Shelf2ndLow=8, Shelf2ndLowQ=9, Shelf2ndHigh=10, Shelf2ndHighQ=11, PeakEQ=12, Notch=13, Bandpass=14, Bessel1stLPF=15, Bessel1stHPF=16, AsymShelf1stLow=17, AsymShelf1stHigh=18, SymShelf1stLow=19, SymShelf1stHigh=20, VariableQLPF=21, VariableQHPF=22.
    FLOAT32* freq;                                // Cutoff frequency of the filter, in Hz.
    FLOAT32* gain;                                // Amount of boost or cut to apply, in dB if applicable.
    FLOAT32* Q;                                   // Specifies the Q of the filter, if applicable.
    fract32* targetCoeffs;                        // Target coefficients in Fract32
    fract32* currentCoeffs;                       // Instantaneous coefficients in Fract32
    fract32* state;                               // State variables. 6 per channel.
} ModuleSOFCascadeHPFract32Class;

Variables

Properties

Name

Type

Usage

isHidden

Default value

Range

Units

numStages

int

const

0

1

1:1:32

smoothingTime

float

parameter

0

0

0:1:1000

msec

updateActive

int

parameter

1

1

0:1

smoothingCoeff

fract32

derived

1

1

Unrestricted

bShift

int

parameter

1

1

Unrestricted

aShift

int

parameter

1

1

Unrestricted

filterType

int*

parameter

0

[1 x 1]

0:22

freq

float*

parameter

0

[1 x 1]

10:0.1:20000

Hz

gain

float*

parameter

0

[1 x 1]

-24:0.1:24

dB

Q

float*

parameter

0

[1 x 1]

0:0.1:20

targetCoeffs

fract32*

derived

0

[5 x 1]

Unrestricted

currentCoeffs

fract32*

state

0

[5 x 1]

Unrestricted

state

fract32*

state

1

[6 x 1]

Unrestricted

Pins

Input Pins

Name: in

Description: audio input

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Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: fract32

MATLAB Usage

File Name: second_order_filter_cascadeHP_fract32_module.m

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