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BiquadSparseV2

Discussion

THIS MODULE IS DEPRECATED AND NOT RECOMMENDED FOR NEW DESIGNS. PLEASE USE THE BiquadSparseV4 MODULE INSTEAD.

This module implements a custom biquad filter that is capable of realizing many different filter types along with additional raw coefficients. 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 filters. First order filters are realized by setting some of the second order coefficients to zero.

The behavior of the cascade filters are controlled by the filterType arrary. The variable, filterType is an integer in the range from 0 to 21 inclusive.

After specifying filterType, adjust the filter parameters by setting the fields, gain, freq, and Q. Some filter parameters are not applicable to all filter types. If the filter type is RawCoeffs then the coefficients from rawCoeffs array used and all other controls ignored. The variable, freq controls the center frequency of the filter, gain determines the boost or cut in dB, and Q determines how sharp the filter is. Low Q values lead to broad filters and high Q values lead to narrow filters.

The following table discusses the various filter types and which variables are active in each case.

filterType=0, Simple pass through with unity gain.

filterType=1, Gain in dB. [gain].

filterType=2, 1st order Butterworth low pass filter. [freq].

filterType=3, 2nd order Butterworth low pass filter. [freq].

filterType=4, 1st order Butterworth high pass filter. [freq].

filterType=5, 2nd order Butterworth high pass filter. [freq].

filterType=6, 1st order allpass filter. [freq].

filterType=7, 2nd order allpass filter. [freq, Q].

filterType=8, 2nd order low shelf. It allows you to vary the gain of the low frequencies. The high frequencies have a gain of 1.0. [freq, gain].

filterType=9, 2nd order low shelf with Q. It allows you to vary the gain of the low frequencies. The high frequencies have a gain of 1.0. [freq, gain, Q].

filterType=10, 2nd order high shelf. It allows you to vary the gain of the high frequencies. The low frequencies have a gain of 1.0. [freq, gain].

filterType=11, 2nd order high shelf with Q. It allows you to vary the gain of the high frequencies. The low frequencies have a gain of 1.0. [freq, gain, Q].

filterType=12, 2nd order peaking filter. It has unity gain except around the specified frequency. By varying gain, you can get a peak or a notch in the frequency band. [freq, gain, Q].

filterType=13, 2nd order notch filter. It has unity gain except around the specified frequency. At the specified frequency, the filter has a true notch with -inf dB gain. [freq, Q].

filterType=14, 2nd order bandpass filter. It has unity gain at the specified frequency and falls off in both directions. The bandwidth of the filter is determined by Q. [freq, Q].

filterType=15, 1st order Bessel low pass filter. [freq].

filterType=16, 1st order Bessel high pass filter. [freq].

filterType=17, 1st order asymmetrical low shelf. [freq, gain].

filterType=18, 1st order asymmetrical high shelf. [freq, gain].

filterType=19, 1st order symmetrical low shelf. [freq, gain].

filterType=20, 1st order symmetrical high shelf. [freq, gain].

filterType=21, raw coefficients from rawCoeffs array.

Module Pack

Advanced

ClassID

classID = 1395

Type Definition

typedef struct _ModuleBiquadSparseV2
{
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.
FLOAT32 convergeTime;                         // Time constant of the cross fading process
INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0).
FLOAT32 smoothingCoeff;                       // Smoothing coefficient. This is computed based on the smoothingTime, sample rate, and block size of the module.
INT32 convergeBlkCnt;                         // Parameter for cross fading.
FLOAT32 oldGain;                              // Gain parameter for cross fading.
FLOAT32 newGain;                              // Gain parameter for cross fading.
INT32 startFading;                            // State variable to implement cross fading.
INT32 rampDown;                               // State variable to implement cross fading.
INT32 currentBlkCnt;                          // Parameter for cross fading.
INT32 enableCrossFading;                      // State variable to implement cross fading.
INT32 onStartup;                              // State variable to implement cross fading.
FLOAT32 bypassLevel;                          // Bypass level during cross fading.
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, RawCoeffs=21.
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* rawCoeffs;                           // Matrix of filter raw coefficients. The size of the matrix is 5 x numStages x numChannels. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
FLOAT32* sofCoeffs;                           // Matrix of filter sof coefficients. The size of the matrix is 5 x numStages x numChannels. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
FLOAT32* currentCoeffs;                       // Matrix of filter current coefficients. The size of the matrix is 5 x numStages x numChannels. Each column contains the variables for a biquad arranged as [b0; b1; b2; a1; a2].
FLOAT32* state;                               // State variables. 2*numChannels per section.
INT32* bypass;                                // State buffer used internally to store coeffs bypass status.
INT32* currentBypass;                         // State buffer used internally to store coeffs bypass status.
} ModuleBiquadSparseV2Class;

Variables

Properties

Name Type Usage isHidden Default Value Range Units
numStages int const 0 2 1:1:100
smoothingTime float parameter 0 10 0:1:1000 msec
convergeTime float parameter 0 10 0:1000 msec
updateActive int parameter 1 0 0:1
smoothingCoeff float derived 1 0.002081 Unrestricted
convergeBlkCnt int derived 1 15 Unrestricted
oldGain float state 1 1 Unrestricted
newGain float state 1 0 Unrestricted
startFading int state 1 1 Unrestricted
rampDown int state 1 1 Unrestricted
currentBlkCnt int state 1 0 Unrestricted
enableCrossFading int state 1 1 Unrestricted
onStartup int state 1 1 Unrestricted
bypassLevel float state 1 1 Unrestricted
filterType int* parameter 0 [2 x 1] 0:21
freq float* parameter 0 [2 x 1] 10:0.1:23990 Hz
gain float* parameter 0 [2 x 1] -24:0.1:24 dB
Q float* parameter 0 [2 x 1] 0:0.1:20
rawCoeffs float* parameter 0 [10 x 1] Unrestricted
sofCoeffs float* derived 0 [10 x 1] Unrestricted
currentCoeffs float* state 1 [10 x 1] Unrestricted
state float* state 1 [4 x 1] Unrestricted
bypass int* state 1 [1 x 1] Unrestricted
currentBypass int* state 1 [1 x 1] Unrestricted

Pins

Input Pins
Name in
Description audio input
Data type float
Channel range Unrestricted
Block size range Unrestricted
Sample rate range Unrestricted
Complex support Real

Output Pins
Name out
Description audio output
Data Type float

Scratch Pins
Channel Count 1
Block size 32
Sample rate 48000

Matlab Usage

File Name: biquad_sparse_v2_module.m 
 M=biquad_sparse_v2_module(NAME, NUMSTAGES, NUMCHANNELS) 
 Creates a Biquad sparse filter that implements a number of standard  
 filter types with additional option to provide raw IIR coefficients.  
 The filter operates on multiple interleaved channels, with different  
 coefficients for each channel.  

 Arguments: 
    NAME - name of the module. 
    NUMSTAGES - number of second order filter stages. 
    NUMCHANNELS - number of channels for the module.

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