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Overview

2nd order filter with coefficients derived from input pins

Discussion

This module implements a general purpose second order 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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The only difference from V2 is an optional argument, BIQUADFORM to select underlying biquad implementation either Direct Form 2 or Direct Form 1. Based on this selection the state buffer is allocated accordingly. Default to use DF-2.

Type Definition

Code Block
typedef struct _ModuleSOFControlV3
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    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, Resonant=23.
    INT32 setBehavior;                            // Controls the Set function calling behavior of the module
    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.
    FLOAT32 smoothingTime;                        // Time constant of the smoothing process.
    INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0).
    FLOAT32 b0;                                   // Desired first numerator coefficient.
    FLOAT32 b1;                                   // Desired second numerator coefficient.
    FLOAT32 b2;                                   // Desired third numerator coefficient.
    FLOAT32 a1;                                   // Desired second denominator coefficient.
    FLOAT32 a2;                                   // Desired third denominator coefficient.
    FLOAT32 current_b0;                           // Instantaneous first numerator coefficient.
    FLOAT32 current_b1;                           // Instantaneous second numerator coefficient.
    FLOAT32 current_b2;                           // Instantaneous third numerator coefficient.
    FLOAT32 current_a1;                           // Instantaneous second denominator coefficient.
    FLOAT32 current_a2;                           // Instantaneous third denominator coefficient.
    FLOAT32 smoothingCoeff;                       // Smoothing coefficient. This is computed based on the smoothingTime, sample rate, and block size of the module.
    UINT32 pinID;                                 // Specifies which control pins are available.
    INT32 biquadForm;                             // Flag indicates which direct form implementation to use, DF-2 or DF-1. Default is DF-2.
    INT32 stateSize;                              // State size per channel. 2 in DF-2 and 4 in DF-1
    FLOAT32* state;                               // State variables. 2 per channel in DF-2 and 4 per channel in DF-1.
    INT32 initDone;                               // For internal use only
} ModuleSOFControlV3Class;

Variables

Properties

Name

Type

Usage

isHidden

Default value

Range

Units

filterType

int

parameter

0

0

0:23

setBehavior

int

parameter

0

0

0:1

freq

float

state

0

250

10:23990

Hz

gain

float

state

0

0

-24:24

dB

Q

float

state

0

1

-20:20

smoothingTime

float

parameter

0

10

0:1000

msec

updateActive

int

parameter

1

1

0:1

b0

float

derived

1

1

Unrestricted

b1

float

derived

1

0

Unrestricted

b2

float

derived

1

0

Unrestricted

a1

float

derived

1

0

Unrestricted

a2

float

derived

1

0

Unrestricted

current_b0

float

state

1

1

Unrestricted

current_b1

float

state

1

0

Unrestricted

current_b2

float

state

1

0

Unrestricted

current_a1

float

state

1

0

Unrestricted

current_a2

float

state

1

0

Unrestricted

smoothingCoeff

float

derived

1

0.06449

Unrestricted

pinID

uint

const

1

7

Unrestricted

biquadForm

int

const

1

0

Unrestricted

stateSize

int

const

1

2

Unrestricted

state

float*

state

1

[2 x 1]

Unrestricted

initDone

int

state

1

Unrestricted

Pins

Input Pins

Name: freqPin

Description: Cutoff frequency of the filter

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Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: float

MATLAB Usage

File Name: sof_control_v3_module.m

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