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(8.D.2.7) SbMultiAECRNSOut

Owned by Sam Stuart
Aug 14, 2024
4 min read

Overview

Multi-channel frequency domain subband adaptive echo cancellation filter

Discussion

Subband based multi channel echo canceller. This module works in conjunction with the WOLA filterbank modules. The module has two input pins. The first input is a single channel microphone signal while the second is a multi-channel reference signal.

At instantiation time you specify the length of each subband filter. Then at run time, you specify the number of taps currently used. This allows you to easily vary the filter length at run time and 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 residual noise calculation gains are stored internally in the W2 state array. W2 is updated every block. If the variable .enableRNS is set, then the output is multiplied by W2.

The module also has an optional output pin that is enabled by the module argument RNSPIN. When this pin exists, the module outputs the RNS weights on the second pin. The RNS output data is real and of dimension 1 x numBins, where numBins is the number of FFT bins.

Type Definition

typedef struct _ModuleSbMultiAECRNSOut { ModuleInstanceDescriptor instance; // Common Audio Weaver module instance structure INT32 maxTaps; // Maximum length of the filter INT32 numChans; // Number of channels for AEC INT32 numXterms; // Number of cross terms for AEC INT32 numTaps; // Current length of the filter FLOAT32 V; // Adaptation constant FLOAT32 smoothingTime; // Time constant of the smoothing process. FLOAT32 A; // Smoothing factor FLOAT32 p0; // Starting value for covariance estimate INT32 numIter; // Number of iterations of adaptive loop - fixed to 1 INT32 enableRNS; // Enable residual noise suppression INT32 numChansX2; // Number of channels multiply by 2 for AEC INT32 numXtermsX2; // Number of cross terms multiply by 2 for AEC 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* Wplus; // Intermediate result (complex scratch). FLOAT32* P; // Real estimation error covariance matrix. FLOAT32* PXTerm; // Estimation error covariance matrix - the off-diagonal terms. FLOAT32* Pplus; // Intermediate result of the diagonals(real scratch). FLOAT32* PplusXTerm; // Estimation error covariance matrix - the off-diagonal terms. FLOAT32* PplusXMatrix; // Estimation error covariance matrix temporary storage (complex scratch). FLOAT32* CC; // Complex state variables (previous inputs). FLOAT32* corrC; // Stores all the correlation between reference signals per bin and tap - diagonal part. Real number. FLOAT32* corrCXTerm; // Correlation between ref channels - the off-diagonal terms. FLOAT32* mu; // Intermediate result (real scratch). FLOAT32* mumu; // Intermediate result (real scratch). FLOAT32* muXTerm; // Intermediate result (imag scratch) - the off-diagonal terms. FLOAT32* mumuXTerm; // Intermediate result (imag scratch) - the off-diagonal terms. FLOAT32* K; // Intermediate K value (imaginary scratch). FLOAT32* KK; // Intermediate K value (imaginary scratch). 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. } ModuleSbMultiAECRNSOutClass;

Variables

Properties

Name

Type

Usage

isHidden

Default value

Range

Units

maxTaps

int

const

0

10

Unrestricted

samples

numChans

int

const

0

2

Unrestricted

 

numXterms

int

const

0

1

Unrestricted

 

numTaps

int

parameter

0

10

1:1:10

samples

V

float

const

0

0.5

Unrestricted

 

smoothingTime

float

parameter

0

10

0.1:1000

sec

A

float

derived

0

1

0:1

 

p0

float

parameter

0

1

Unrestricted

 

numIter

int

const

0

1

1:1

 

enableRNS

int

parameter

0

1

0:1:1

 

numChansX2

int

const

1

4

Unrestricted

 

numXtermsX2

int

const

1

2

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

[20 x 32]

Unrestricted

 

Wplus

float*

state

0

[1 x 1]

Unrestricted

 

P

float*

state

0

[20 x 32]

Unrestricted

 

PXTerm

float*

state

0

[10 x 32]

Unrestricted

 

Pplus

float*

state

0

[10 x 1]

Unrestricted

 

PplusXTerm

float*

state

0

[1 x 1]

Unrestricted

 

PplusXMatrix

float*

state

0

[8 x 1]

Unrestricted

 

CC

float*

state

0

[20 x 32]

Unrestricted

 

corrC

float*

state

0

[20 x 32]

Unrestricted

 

corrCXTerm

float*

state

0

[10 x 32]

Unrestricted

 

mu

float*

state

0

[1 x 1]

Unrestricted

 

mumu

float*

state

0

[20 x 1]

Unrestricted

 

muXTerm

float*

state

0

[1 x 1]

Unrestricted

 

mumuXTerm

float*

state

0

[10 x 1]

Unrestricted

 

K

float*

state

0

[1 x 1]

Unrestricted

 

KK

float*

state

0

[20 x 1]

Unrestricted

 

W2

float*

state

0

[32 x 1]

Unrestricted

 

RNS_table

float*

parameter

0

[2 x 7]

Unrestricted

 

RNS_polyCoeffs

float*

state

1

[4 x 6]

Unrestricted

 

Pins

Input Pins

Name: dataIn

Description: Microphone input

Data type: float

Channel range: 1

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Complex

 

Name: reference

Description: Reference input

Data type: float

Channel range: 2

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Complex

Output Pins

Name: errorSignal

Description: Error signal = difference between filter output and dataIn

Data type: float

 

Name: RNSWeights

Description: Weights from the residual noise suppressor

Data type: float

MATLAB Usage

File Name: sb_multi_aec_rns_out_module.m

M = sb_multi_aec_rns_out_module(NAME, MAXTAPS, NUMCHANS, RNSPIN) Frequency domain subband multi-channel echo canceler using a Kalman filter based algorithm. Arguments: NAME - name of the module. MAXTAPS - maximum length of each frequency domain complex adaptive filter NUMCHANS - number of reference channels RNSPIN - Boolean which specifies that the pin will have a second output pin containing the RNS data. This wire holds real data of size 1 x numBins. By default RNSPIN = 0.

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