Overview

Linkwitz-Riley filter

Discussion

The module provides Linkwitz-Riley low pass, high pass, or all pass filters, from 2nd order to 10th order. Linkwitz-Riley filters can only have an even order. The module operates on 32-bit floating-point data. The order of the filter is determined by the order argument when instantiated, and the filterType parameter is used to select which type of filter is designed. Once the order is set, it cannot be changed. The filterType parameter is able to be changed at run-time. filterType=0 designs a low pass filter. filterType=1 designs a high pass filter. filterType=2 designs an allpass filter.

Please note that if you are using the module as part of a crossover network (such as a lowpass & highpass combination) in order to achieve a flat unity output, if order/2 is an odd number you need to invert the output (multiply the data by -1) of one of the sections. Addtionally, allpass filters are only supported if order/2 is odd. If you try and build an allpass when order/2 is even, you will get a warning message.

Type Definition

typedef struct _ModuleLinkwitzRileyFilter
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 filterType;                             // Specifies what type of filter is designed (lowpass=0, highpass=1, allpass=2).
    INT32 order;                                  // Order of the filter.
    FLOAT32 cutoff;                               // Cutoff frequency of the filter in Hz - range clamped to calc based on sample rate
    awe_modButterworthFilterInstance *butter1; // Butterworth filter
    awe_modButterworthFilterInstance *butter2; // Butterworth filter
} ModuleLinkwitzRileyFilterClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
filterType	int	parameter	0	0	0:2
order	int	const	0	2	2:10
cutoff	float	parameter	0	250	1:0.1:20000	Hz

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: linkwitz_riley_filter_module.m

 SYS=linkwitz_riley_filter_module(NAME, ORDER)
 Creates a Linkwitz Riley high-pass, low-pass, or all-pass filter.
 
 Arguments:
    NAME - name of the module.
    ORDER - filter order.cd