Overview

DSP Concepts proprietary Single-Channel Noise Reduction. Version 2.

Discussion

DSP Concepts proprietary Single-Channel Noise Reduction module. This module works in conjunction with the WOLA filterbank modules. The module supports any number of channels and applies noise reduction independently to each. The input pin is mic input signal and output pin is stationary noise-suppressed signal. There is an optional 2nd output pin that outputs noise masking gain for each frequency

The module operates on any number of channels, any block size, and any sampling rate. At design time, you specify the number of channels and whether the output noise suppression mask gain output pin is active. At run time, the strength of noise suppression can be controlled by specifyin minGaindB and noiseAdjustdB The tunable parameter minGaindB is a lower clipping point of gain in dB for each frequency bin. minGaindB is a negative number in the range [-20 0]. Setting minGaindB = -10 means that the module will apply at most -10 dB of attenuation in a subband.

noiseAdjustdB is an offset which is added to the estimated noise floor. Stationary noise floor estimation is prone to be lower than actual noise level. By setting noiseAdjustdB to a positive number the algorithm will assume a higher noise floor and be more aggressive.

Smaller minGaindB and/or larger noiseAdjustdB setting configures noise suppression more aggressive. The module estimates SNR and determines attenuation of each frequency from gain table.

The module can be configured to output an optional 2nd output pin. This pin holds the instantaneous gain reduction (as a linear value) that is applied to each subband.

Type Definition

typedef struct _ModuleSCNRv2
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 minGaindB;                            // the minimum gain to be applied in dB
    FLOAT32 noiseAdjustdB;                        // noise level adjustment in dB.
    FLOAT32 minGain;                              // the minimum gain to be applied in linear.
    FLOAT32 noiseAdjust;                          // noise level adjustment in linear.
    FLOAT32 attackTime;                           // Internal coefficient realizing the attack time.
    FLOAT32 attackCoeff;                          // Internal coefficient realizing the attack time.
    FLOAT32 freq1;                                // Internal coefficient realizing the attack time.
    FLOAT32 b0_1;                                 // Desired first numerator coefficient.
    FLOAT32 b1_1;                                 // Desired second numerator coefficient.
    FLOAT32 a1_1;                                 // Desired second denominator coefficient.
    FLOAT32 freq2;                                // Internal coefficient realizing the attack time.
    FLOAT32 b0_2;                                 // Desired first numerator coefficient.
    FLOAT32 b1_2;                                 // Desired second numerator coefficient.
    FLOAT32 a1_2;                                 // Desired second denominator coefficient.
    FLOAT32 ppriorTimeConst;                      // Internal coefficient realizing the attack time.
    FLOAT32 ppriorEta;                            // Internal coefficient realizing the attack time.
    FLOAT32* pxState;                             // Sb smoothing state for Px computation.
    FLOAT32* pshatState;                          // Sb smoothing state for Ps_hat computation.
    FLOAT32* gainState;                           // Sb smoothing state for gain computation.
    FLOAT32* pnEnvState;                          // Attack release env state for Pn computation.
    FLOAT32* prevPsHat;                           // Feedback memory.
    FLOAT32* maskGain;                            // Noise suppression mask gain.
} ModuleSCNRv2Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
minGaindB	float	parameter	0	-12	-20:1:0	dB
noiseAdjustdB	float	parameter	0	6	0:1:12	dB
minGain	float	derived	1	0.25119	Unrestricted
noiseAdjust	float	derived	1	3.9811	Unrestricted
attackTime	float	const	1	2000	Unrestricted
attackCoeff	float	derived	1	1.0417e-05	Unrestricted
freq1	float	const	1	12	Unrestricted
b0_1	float	derived	1	0.00078478	Unrestricted
b1_1	float	derived	1	0.00078478	Unrestricted
a1_1	float	derived	1	0.99843	Unrestricted
freq2	float	const	1	5	Unrestricted
b0_2	float	derived	1	0.00032714	Unrestricted
b1_2	float	derived	1	0.00032714	Unrestricted
a1_2	float	derived	1	0.99935	Unrestricted
ppriorTimeConst	float	const	1	311.9	Unrestricted
ppriorEta	float	derived	1	0.99993	Unrestricted
pxState	float*	state	1	[1 x 32]	Unrestricted
pshatState	float*	state	1	[1 x 32]	Unrestricted
gainState	float*	state	1	[1 x 32]	Unrestricted
pnEnvState	float*	state	1	[1 x 32]	Unrestricted
prevPsHat	float*	state	1	[1 x 32]	Unrestricted
maskGain	float*	state	1	[1 x 33]	Unrestricted

Pins

Input Pins

Name: in

Description: Audio input

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Complex

Output Pins

Name: out

Description: audio output

Data type: float

Name: maskGain

Description: SCNR mask gain

Data type: float

MATLAB Usage

File Name: scnr_v2_module.m

 M = scnr_v1_module(NAME)
 Single-channel noise reduction module.  This module reduces stationary 
 noise floor level.  Arguments:
   NAME - name of the module
   NUMCHANS - number of channels to process.  Default=1.
   OUTPUTMASKGAIN - Boolean which specifies whether the module has a
     second output pin containing the instantaeous gains applied to each
     subband.