SbAECReset
Overview
Frequency domain subband adaptive filter
Discussion
Subband based mono echo canceler. 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 and the second is a mono 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
Type Definition
typedef struct _ModuleSbAECReset
{
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
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
INT32 enableRNS; // Enable residual noise suppression
FLOAT32 bypassTime; // Time in millisecond that it takes the system to reconverge after it is bypassed
INT32 bypassBlocks; // Number of processing blocks that we count up as we time the bypass operation
INT32 bypassCount; // Internal counter while AEC is bypassed
INT32 bypassOn; // Indicates when the module is in bypass mode
FLOAT32 PResetValue; // P matrix is set to this value after reset
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* Pplus; // Intermediate result (real scratch).
FLOAT32* Wplus; // Intermediate result (complex scratch).
FLOAT32* energyC; // Intermediate result (real scratch).
FLOAT32* mu; // Intermediate result (real 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.
} ModuleSbAECResetClass;
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 | 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 | parameter | 0 | 1 | 1:20 | |
enableRNS | int | parameter | 0 | 1 | 0:1:1 | |
bypassTime | float | parameter | 0 | 2000 | Unrestricted | |
bypassBlocks | int | derived | 0 | 96000 | Unrestricted | |
bypassCount | int | state | 0 | 0 | Unrestricted | |
bypassOn | int | state | 0 | 0 | Unrestricted | |
PResetValue | float | parameter | 0 | 0.001 | 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 | [16 x 32] | Unrestricted | |
P | float* | state | 0 | [16 x 32] | Unrestricted | |
CC | float* | state | 0 | [16 x 32] | Unrestricted | |
Pplus | float* | state | 0 | [1 x 16] | Unrestricted | |
Wplus | float* | state | 0 | [1 x 16] | Unrestricted | |
energyC | float* | state | 0 | [16 x 32] | Unrestricted | |
mu | float* | state | 0 | [1 x 16] | 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: reset
Description: Resets internal state
Data type: int
Channel range: 1
Block size range: 1
Sample rate range: Unrestricted
Complex support: Real
Name: dataIn
Description: Micro 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: 1
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
MATLAB Usage
File Name: sb_aec_reset_module.m
M = sb_aec_reset_module(NAME, MAXTAPS)
Frequency domain subband echo canceler using a Kalman filter based
algorithm. This version includes a reset pin allowing the internal
module state variables to be reset in case they lock up. Arguments:
NAME - name of the module.
MAXTAPS - maximum length of each frequency domain complex adaptive filter