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Overview

General 2nd order filter cascade designer with smoothing

Discussion

This module implements a general purpose second order filter Cascade 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 Cascade 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 _ModuleSOFSmoothedCascadeFract32
{
    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 postShift;                              // Number of bits to shift
    FLOAT32 twoPowMinusPostShift;                 // 2^(-postShift). Used by to streamline the operation of the set function
    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
    FLOAT32* gain;                                // Amount of boost or cut to apply, in decibels (if applicable)
    FLOAT32* Q;                                   // Specifies the Q of the filter, if applicable
    FLOAT32* coeffs;                              // coefficients
    fract32* target_coeffsFract32;                // Matrix of filter coefficients. The size of the matrix is 5 x numStages. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
    fract32* current_coeffsFract32;               // Matrix of filter coefficients. The size of the matrix is 5 x numStages. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
    fract32* state;                               // State variables. 4 per channel per stage
} ModuleSOFSmoothedCascadeFract32Class;

Variables

Properties

Name

Type

Usage

isHidden

Default value

Range

Units

numStages

int

const

0

2

1:1:32

smoothingTime

float

parameter

0

10

0:1:1000

msec

updateActive

int

parameter

1

1

0:1

smoothingCoeff

fract32

derived

1

0.06449

Unrestricted

postShift

int

derived

1

1

Unrestricted

twoPowMinusPostShift

float

derived

1

0.5

Unrestricted

filterType

int*

parameter

0

[1 x 2]

0:22

freq

float*

parameter

0

[1 x 2]

10:0.1:23990

Hz

gain

float*

parameter

0

[1 x 2]

-24:0.1:24

dB

Q

float*

parameter

0

[1 x 2]

0:0.1:20

coeffs

float*

parameter

0

[5 x 2]

Unrestricted

target_coeffsFract32

fract32*

derived

0

[5 x 2]

Unrestricted

current_coeffsFract32

fract32*

state

0

[5 x 2]

Unrestricted

state

fract32*

state

1

[4 x 2]

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_cascade_fract32_module.m

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