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
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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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