XAUDIO2_FILTER_PARAMETERS structure (xaudio2.h)

Article
10/05/2021

Defines filter parameters for a source voice.

Syntax

typedef struct XAUDIO2_FILTER_PARAMETERS {
  XAUDIO2_FILTER_TYPE Type;
  float               Frequency;
  float               OneOverQ;
} XAUDIO2_FILTER_PARAMETERS;

Members

Type

The XAUDIO2_FILTER_TYPE.

Frequency

Filter radian frequency calculated as (2 * sin(pi * (desired filter cutoff frequency) / sampleRate)). The frequency must be greater than or equal to 0 and less than or equal to XAUDIO2_MAX_FILTER_FREQUENCY. The maximum frequency allowable is equal to the source sound's sample rate divided by six which corresponds to the maximum filter radian frequency of 1. For example, if a sound's sample rate is 48000 and the desired cutoff frequency is the maximum allowable value for that sample rate, 8000, the value for Frequency will be 1. If XAUDIO2_HELPER_FUNCTIONS is defined, XAudio2.h will include the XAudio2RadiansToCutoffFrequency and XAudio2CutoffFrequencyToRadians helper functions for converting between hertz and radian frequencies. Defining XAUDIO2_HELPER_FUNCTIONS will also include XAudio2CutoffFrequencyToOnePoleCoefficient for converting between hertz and a one-pole coefficient suitable for use with the LowPassOnePoleFilter and HighPassOnePoleFilter.

OneOverQ

Reciprocal of Q factor. Controls how quickly frequencies beyond Frequency are dampened. Larger values result in quicker dampening while smaller values cause dampening to occur more gradually. Must be greater than 0 and less than or equal to XAUDIO2_MAX_FILTER_ONEOVERQ.

Remarks

Setting XAUDIO2_FILTER_PARAMETERS with the following values is acoustically equivalent to the filter being fully bypassed.

XAUDIO2_FILTER_PARAMETERS FilterParams;
FilterParams.Frequency = 1.0f;    
FilterParams.OneOverQ = 1.0f;
FilterParams.Type = LowPassFilter;

The following formulas show the relationship between the members of XAUDIO2_FILTER_PARAMETERS and the per-voice filter.

Yl( n ) = F1 yb( n ) + yl( n - 1 )
Yb( n ) = F1 yh( n ) + yb( n - 1 )
Yh( n ) = x( n ) - yl( n ) - OneOverQ(yb( n - 1 )
Yn( n ) = Yl(n) + Yh(n)

Where:

Yl = lowpass output
Yb = bandpass output
Yh = highpass output
Yn = notch output
F1 = XAUDIO2_FILTER_PARAMETERS.Frequency
OneOverQ = XAUDIO2_FILTER_PARAMETERS.OneOverQ

Platform Requirements

Windows 10 (XAudio2.9); Windows 8, Windows Phone 8 (XAudio 2.8); DirectX SDK (XAudio 2.7)

Requirements

Requirement	Value
Header	xaudio2.h

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