Overview

Three band equalizer

Discussion

This module implements a three band tone control fixed point module. Low shelf filter is used for low frequency band with normalised gain with respect to mid band gain. Similarly for high frequency band high shelf filter is used with normalised gain with respect to mid gain. Finally scale smoothely the entire signal with mid band gain.

Type Definition

typedef struct _ModuleThreeBandToneControlFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 smoothingTime;                        // Time constant of the smoothing process
    FLOAT32 lowFreq;                              // Low band center frequency, in Hz
    FLOAT32 midFreq;                              // Mid band center frequency, in Hz
    FLOAT32 highFreq;                             // High band center frequency, in Hz
    FLOAT32 lowGain;                              // Low band gain, in dB
    FLOAT32 midGain;                              // Mid band gain, in dB
    FLOAT32 highGain;                             // High band gain, in dB
    INT32 headRoomBits;                           // Head room bits. This prevents internal clipping in the filter stages
    INT32 postShift;                              // postShift controls the headroom within the fixed-point filtering
    FLOAT32 twoPowMinusPostShift;                 // Two power -postShift value
    INT32 filterUpdateActive;                     // Boolean that is set when updating coefficients
    fract32 smoothingCoeff;                       // Smoothing coefficient for the filter coefficients
    fract32 midTargetGain;                        // Target gain of the mid frequency gain
    fract32 midCurrentGain;                       // Current gain of the mid frequency gain
    fract32 midSmoothingCoeff;                    // Sample-by-sample smoothing coefficient of the mid frequency gain
    fract32* lowerTargetCoeffs;                   // Target coefficients for the low frequency shelf
    fract32* lowerCurrentCoeffs;                  // Current coefficients for the low frequency shelf
    fract32* lowerState;                          // State variables for the low frequency shelf
    fract32* upperTargetCoeffs;                   // Target coefficients for the high frequency shelf
    fract32* upperCurrentCoeffs;                  // Current coefficients for the high frequency shelf
    fract32* upperState;                          // State variables for the high frequency shelf
} ModuleThreeBandToneControlFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
smoothingTime	float	parameter	0	20	0:1000	msec
lowFreq	float	parameter	0	60	30:200	Hz
midFreq	float	parameter	0	600	200:4000	Hz
highFreq	float	parameter	0	6000	4000:20000	Hz
lowGain	float	parameter	0	0	-12:12	dB
midGain	float	parameter	0	0	-12:12	dB
highGain	float	parameter	0	0	-12:12	dB
headRoomBits	int	parameter	1	2	Unrestricted
postShift	int	parameter	1	5	Unrestricted
twoPowMinusPostShift	float	parameter	1	0.03125	Unrestricted
filterUpdateActive	int	parameter	1	1	Unrestricted
smoothingCoeff	fract32	parameter	1	0.03278	Unrestricted
midTargetGain	fract32	parameter	1	0.03125	Unrestricted
midCurrentGain	fract32	parameter	1	0.03125	Unrestricted
midSmoothingCoeff	fract32	parameter	1	0.001041	Unrestricted
lowerTargetCoeffs	fract32*	parameter	1	[5 x 1]	Unrestricted
lowerCurrentCoeffs	fract32*	parameter	1	[5 x 1]	Unrestricted
lowerState	fract32*	state	1	[4 x 1]	Unrestricted
upperTargetCoeffs	fract32*	parameter	1	[5 x 1]	Unrestricted
upperCurrentCoeffs	fract32*	parameter	1	[5 x 1]	Unrestricted
upperState	fract32*	state	1	[4 x 1]	Unrestricted

Pins

Input Pins

Name: in

Description: audio input

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: fract32

Scratch Pins

Channel count: 1

Block size: 32

Sample rate: 48000

MATLAB Usage

File Name: three_band_tone_control_fract32_module.m

 M=three_band_tone_control_fract32_module(NAME)
 Implements a three band tone control module.
 Arguments:
    NAME - name of the module.