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There are 5 coefficients that the user must set: b₀, b₁, b₂, a₁, and a₂ (a₀ is always assumed to be 1). Audio Weaver does not check for stability and care must be used when computing the filter coefficients. There are several variants of Biquad filters. The simples – Biquad – has a single stage and implements the different equation shown above. BiquadCascade implements N stages of filtering with each channel using the same coefficients. BiquadNCascade implements N stages with each channel have its own set of coefficients. Finally, BiquadSmoothed implements a single Biquad stage with coefficient smoothing on a block-by-block basis.

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Image Added	FIR	Time domain FIR filter Specify filter length in module properties
Image Added	Biquad	Second order IIR filter. 5 filter coefficients are specified. No smoothing.
Image Added	BiquadCascade	Multiple Biquad filters in series. The number of filters is specified in module properties. The same coefficients are used per channel.
Image Added	BiquadSmoothed	Second order IIR filter. 5 filter coefficients are specified. Smoothed on a block-by-block basis
Image Added	BiquadNCascade	Multiple Biquad filters in series. The number of filters is specified in module properties. Different coefficients are used per channel.
Image Added	FIR Sparse	Sparse FIR filter in which most values are zero. Less convolution cycles than normal FIR
Image Modified	FIR Sparse Reader	Sparse FIR that connects to a delay state writer. Convolution is based on a pointer rather than a separate FIR buffer.
Image Added	FIR Sparse Reader Fract16	Like FIR Sparse Reader except half the memory. Data is converted to fract16 for computations and has a conversion for the output if necessary.

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High Precision Filters

Audio Weaver contains a variety of Biquad filters for equalizing audio. Some filters require raw coefficients (such as Biquad or BiquadCascade) while others contain built-in design equals (such as the SecondOrderFilter or ButterworthFilter). These filters are implemented using a Direct Form 2 (DF2) structure:

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All Biquad filters including the DF2 have 5 coefficients. The advantage of the DF2 structure is that it requires only 2 state variables per filter as compared to 4 state variables for the DF1 structure.

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The High Precision modules are designed to be drop in replacements for the non-high precision filters. That way, numerical problems can be resolved by replacing the offending filter with its high precision version.

Image Added	BiqudSmoothedHP	Smoothly varying Biquad
Image Added	ButterworthFilterHP	Butterworth lowpass, highpass, and allpass filters
Image Added	BiquadCascadeHP	Cascade of N Biquad stages
Image Added	GraphicEQBandHP	Single band of a graphic equalizer
Image Added	SOFControlHP	Controllable second order filter with design equations
Image Added	SOFCascadeHP	Cascade of second order filters each with design equations
Image Added	SecondOrderFilterHP	Single second order filter with design equations
Image Added	VolumeControlHP	Fletcher Munson volume control with loudness compensation

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