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(8.D.2.7) SbKalmanAECMonoV1

Owned by Sam Stuart
Aug 14, 2024
8 min read

Overview

Frequency domain subband Kalman filter

Discussion

Subband Kalman based mono echo canceler with support for multiple input channels.

I/O Pins

This module works in conjunction with the WOLA filterbank modules and accepts complex data. The default module has two input pins, and one output pin. The first input can have any number of microphone signals, while the second is the mono reference signal. The reference signals and states are shared among the microphones, saving memory and MIPS over using several instances. The error output pin will have one channel per microphone input.

User Parameters

At instantiation time the maximum number of taps must be defined. The number of taps actually used is the parameter numTaps, found in the module inspector or the module properties view. numTaps allows you to vary the filter length at runtime to verify performance and CPU load.

The module has optional residual noise suppression which is enabled via the enableRNS variable. By default, residual noise suppression is on and the output of the echo canceler (the error signal) is further reduced in level. The residual noise suppression is configured by a 7 element interpolation table. This table operates just like the Table X-Y module with configurable (X, Y) lookup points. The lookup table specifies values in dB for the input and output function

The p0 variable is used to initialize the P array at startup time and during any reset events triggered by the optional input pins. p0 defaults to 1.0. Changing this value during runtime will automatically reset P to the new value.

The smoothingTime variable, with units of seconds, is a state transition factor analogous to the leakage factor in a leaky lms algorithm. It defaults to 30, which has a convergence time roughly equivalent to a setting of 100 in the deprecated SbAECV1 module.

The FFTSize parameter is set at instantiation and used to calculate an internal adaptation constant. This is normally the FFT size of the WOLA Analysis module upstream of this module. FFTSize is often (blocksize-1) * 2 unless sub bands are split to multiple AECs.

Optional Input Pins

Three additional input pins will be added to the module if the resetPinsEn module argument is set to true. These control pins can be used to modify the behavior of the module during runtime, as described below:

resetP: This pin has one INT32 value per microphone channel. If the value is not zero, then that microphone's P array will be reset to the current p0 value each pump.

masterReset: This pin has only a single INT32 value and one channel. If the value is not zero, then all internal states and weight arrays will be reset to their default values for all microphone channels. This includes the P array.

freeze: This pin has one INT32 value per microphone channel. If the value is not zero, then the adaptation stage of the filter will not run for that channel. The existing weights will continue to be applied, but they will not be updated again until the freeze is set to zero. This does not include the RNS weights since they are highly dependent on reference levels.

Optional Output Pins

Three module arguments can be used to add additional output pins, which can be useful for debugging purposes.

outputRNSWeights: Enabling this will output the RNS weights (the W2 array) on an output pin. The output pin will have one channel per microphone. The W2 weights are real and there is one value per input bin. If this pin is enabled, then the W2 weights are not applied to the output error signal.

outputAECWeights: This argument will output the AEC weights (the WW1 array) on an output pin if set to true. This output pin will have maxTaps channels per microphone input. The WW1 weights are complex, and they are ordered [t1c1 t1c2 ... t1cC t2c1 t2c2 ... tTcC], where t# is tap number, T is maxTaps, c# is channel number, and C is number of channels.

outputPVals: If set to true, this argument will enable an output pin for the P array. The P array is all real values, and is ordered per microphone channel as [b1t1 b1t2 ... b1tT b2t1 ... bBtT bBtT], where t# is tap number, T is maxTaps, b# is bin number, and B is number of input bins.

Type Definition

typedef struct _ModuleSbKalmanAECMonoV1 { ModuleInstanceDescriptor instance; // Common Audio Weaver module instance structure INT32 maxTaps; // Maximum length of the filter INT32 numTaps; // Current length of the filter FLOAT32 V; // Adaptation constant based on num taps and fft size FLOAT32 smoothingTime; // Time constant of the smoothing process. FLOAT32 A; // Smoothing factor FLOAT32 p0; // Starting value for covariance estimate INT32 enableRNS; // Enable residual noise suppression INT32 firstRun; // First run for setting P from p0 on startup FLOAT32 FFTSize; // FFT Size used for input bins INT32 enableResets; // tracker for if the reset pins are visible INT32 enableW2Output; // tracker for rns weight output enable INT32 enableWOutput; // tracker for aec weight output enable INT32 enablePVOutput; // tracker for rns weight output enable INT32 scratchIndex; // tracker for which pin scratch is on INT32 stateIndex; // Circular buffer index. [0 numTaps-1] INT32 RNS_numPoints; // Number of values in the lookup table. The total table size is [maxPoints 2]. INT32 RNS_order; // Order of the interpolation. This can be either 2 (for linear) or 4 (for pchip). FLOAT32* WW1; // Adaptive filter coefficients. FLOAT32* P; // Real estimation error covariance matrix. FLOAT32* CC; // Complex state variables (previous inputs). FLOAT32* W2; // Residual noise suppression weights. FLOAT32* RNS_table; // Lookup table. The first row is the X values and the second row is the Y values. FLOAT32* RNS_polyCoeffs; // Interpolation coefficients returned by the grid control. } ModuleSbKalmanAECMonoV1Class;

Variables

Properties

Name

Type

Usage

isHidden

Default value

Range

Units

maxTaps

int

const

0

16

Unrestricted

samples

numTaps

int

parameter

0

16

1:1:16

samples

V

float

derived

0

1.0302

Unrestricted

 

smoothingTime

float

parameter

0

10

0.1:1000

sec

A

float

derived

0

1

0:1

 

p0

float

parameter

0

1

Unrestricted

 

enableRNS

int

parameter

0

1

0:1:1

 

firstRun

int

state

0

0

Unrestricted

 

FFTSize

float

derived

1

512

Unrestricted

 

enableResets

int

const

1

0

Unrestricted

 

enableW2Output

int

const

1

0

Unrestricted

 

enableWOutput

int

const

1

0

Unrestricted

 

enablePVOutput

int

const

1

0

Unrestricted

 

scratchIndex

int

const

1

3

Unrestricted

 

stateIndex

int

state

1

0

Unrestricted

 

RNS_numPoints

int

const

1

7

4:1:1000

 

RNS_order

int

const

1

2

2:2:4

 

WW1

float*

state

0

[512 x 1]

Unrestricted

 

P

float*

state

0

[512 x 1]

Unrestricted

 

CC

float*

state

0

[16 x 32]

Unrestricted

 

W2

float*

state

0

[32 x 1]

Unrestricted

 

RNS_table

float*

parameter

1

[2 x 7]

Unrestricted

 

RNS_polyCoeffs

float*

state

1

[4 x 6]

Unrestricted

 

Pins

Input Pins

Name: dataIn

Description: Mic inputs

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Complex

 

Name: reference

Description: Reference input

Data type: float

Channel range: 1

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Complex

Output Pins

Name: errorSignal

Description: Error signal = difference between filter output and each channels data input

Data type: float

Scratch Pins

Channel count: 1

Block size: 544

Sample rate: 48000

MATLAB Usage

File Name: sb_kalman_aec_mono_v1_module.m

M = sb_kalman_aec_mono_v1_module(NAME, MAXTAPS, FFTSIZE, RESETPINSENABLE, OUTPUTRNSWEIGHTS, OUTPUTAECWEIGHTS, OUTPUTPVALS)) Frequency domain subband mono echo canceler using a Kalman filter based algorithm. Arguments: NAME - name of the module. MAXTAPS - maximum length of each frequency domain complex adaptive filter FFTSIZE - fft size used for input data (typically (# WOLA subbands-1)*2 RESETPINSENABLE - creates 3 optional input pins for controlling behavior of module. - The resetP pin resets all P values to initial p0 value - The masterReset pin resets all internal states to initial values (including P) for all channels - The freeze pin can freeze the adaptation in the filter. Current weights are still applied OUTPUTRNSWEIGHTS - optional output pin for RNS weights OUTPUTAECWEIGHTS - optional output pin for AEC weights OUTPUTPVALS - optional output pin for P values Copyright 2020. DSP Concepts, Inc. All Rights Reserved.

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