Overview

DSP Concepts proprietary single-channel Noise Tracking.

Discussion

This module estimates the stationary-noise level of its incoming signal. It is part of the SCNRv4 design, but can be used independently.

The module works in conjunction with the WOLA filterbank modules.

The input pin expects the squared-magnitude of the WOLA-domain noisy signal, while the output pin provides the noise-level estimate in dBs.

The module is single channel, expects real data, and operates on any block size and any sampling rate.

At design time, the initial noise estimate must be set using noiseLevelInitdB.

The noiseAdjustdB parameter is an offset which is added to the estimated noise dB-level. The stationary noise-floor estimation is prone to be lower than the actual noise level. By setting noiseAdjustdB to a positive number, the algorithm will bias the estimated level to be higher.

The estimated level is smoothed out using cross-bin averaging in logarithmic groupings. The noiseSmoothOctave parameter defines how many octaves the averaging should span. Smoothing can be disabled by setting noiseSmoothOctave to 0.

The noise floor (minimum noise-estimate) can be set via noiseFloordB.

The trackingSpeed parameter controls the tracking speed of the algorithm. It can take values between 0 (low speed) and 2 (high speed), with a default value of 1.

The sensitivity parameter controls the sensitivity of the algorithm to small level fluctuations. It affects the estimation bias, but also the overall tracking speed of the algorithm. It is recommended using all 3 parameters (sensitivity, trackingSpeed and noiseAdjustdB) to achieve the desired behaviour. It takes values between 0 (low sensitivity) and 2 (high sensitivity), with a default value of 1.

The module has 2 extra optional inputs:

The ctrlUp and ctrlDown inputs have the same attributes (block size and sample rate) as the noisy signal. They should be valued 0 or 1 only. These are used to freeze the noise trackers on the way up or down, respectively. A value of 1 means adapt, while a value of 0 means freeze.

Type Definition

typedef struct _ModuleNoiseTracking
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 snrCtrlAttRelHoldCount;                 // Hold time translated to the number of blocks.
    FLOAT32 snrCtrlAttRelAttCoeff;                // Internal coefficient realizing the attack time.
    FLOAT32 snrCtrlAttRelRelCoeff;                // Internal coefficient realizing the release time.
    INT32 snrAdjustAttRelHoldCount;               // Hold time translated to the number of blocks.
    FLOAT32 snrAdjustAttRelAttCoeff;              // Internal coefficient realizing the attack time.
    FLOAT32 snrAdjustAttRelRelCoeff;              // Internal coefficient realizing the release time.
    INT32 snrAdjustAttRel2HoldCount;              // Hold time translated to the number of blocks.
    FLOAT32 snrAdjustAttRel2AttCoeff;             // Internal coefficient realizing the attack time.
    FLOAT32 snrAdjustAttRel2RelCoeff;             // Internal coefficient realizing the release time.
    FLOAT32 snrAdjustScaleOffOffset;              // Scale Offset offset.
    INT32 snrAttRelHoldCount;                     // Hold time translated to the number of blocks.
    FLOAT32 snrAttRelAttCoeff;                    // Internal coefficient realizing the attack time.
    FLOAT32 snrAttRelRelCoeff;                    // Internal coefficient realizing the release time.
    FLOAT32 snrScaleOff1Offset;                   // Scale Offset offset.
    FLOAT32 snrScaleOff2Offset;                   // Scale Offset offset.
    INT32 noiseAttRelHoldCount;                   // Hold time translated to the number of blocks.
    FLOAT32 noiseAttRelAttCoeff;                  // Internal coefficient realizing the attack time.
    FLOAT32 noiseAttRelRelCoeff;                  // Internal coefficient realizing the release time.
    FLOAT32 noiseSofB0;                           // Desired first numerator coefficient.
    FLOAT32 noiseSofB1;                           // Desired second numerator coefficient.
    FLOAT32 noiseSofA1;                           // Desired second denominator coefficient.
    FLOAT32 noiseAdjustdB;                        // Noise level bias in dB.
    FLOAT32 noiseScaleOffGain;                    // Scale Offset linear gain.
    FLOAT32 noiseSmoothOctave;                    // Number of octaves for cross-bin logarithmic smoothing.
    FLOAT32 araAlphaCalcUpScaleOff2Offset;        // Scale Offset offset.
    FLOAT32 araScaleOffOffset;                    // Scale Offset offset.
    FLOAT32 noiseFloordB;                         // Noise floor level in dB.
    FLOAT32 noiseFloorLinear;                     // Noise floor level linear.
    FLOAT32 trackingSpeed;                        // Noise-tracking speed.
    FLOAT32 sensitivity;                          // Sensitivity to small-level fluctuations.
    INT32 enableControlInputs;                    // Tracker for input control pins enable
    FLOAT32 snrCtrlAttRelAttack;                  // Attack time in ms.
    FLOAT32 snrCtrlAttRelRelease;                 // Release time in ms.
    FLOAT32 snrCtrlAttRelHold;                    // Hold time in ms.
    FLOAT32 snrAdjustAttRelAttack;                // Attack time in ms.
    FLOAT32 snrAdjustAttRelRelease;               // Release time in ms.
    FLOAT32 snrAdjustAttRelHold;                  // Hold time in ms.
    FLOAT32 snrAdjustAttRel2Attack;               // Attack time in ms.
    FLOAT32 snrAdjustAttRel2Release;              // Release time in ms.
    FLOAT32 snrAdjustAttRel2Hold;                 // Hold time in ms.
    FLOAT32 snrAdjustThreshdB;                    // SNR adjustment threshold in dB.
    FLOAT32 snrAdjustClipAsymUpper;               // Asymmetric-clip upper limit.
    FLOAT32 snrAttRelAttack;                      // Attack time in ms.
    FLOAT32 snrAttRelRelease;                     // Release time in ms.
    FLOAT32 snrAttRelHold;                        // Hold time in ms.
    FLOAT32 noiseSmoothWidth;                     // Control-chain cross-bin linear-smoothing coefficient (fraction of sample rate).
    FLOAT32 snrSmoothStartFreq;                   // Start frequency for cross-bin smoothing.
    FLOAT32 noiseStepUpdBDef;                     // Noise step up default in dB/s.
    FLOAT32 noiseStepUpdBMaxDev;                  // Noise step up max deviation in dB/s.
    FLOAT32 noiseStepDowndB;                      // Noise step down in dB/s.
    FLOAT32 noiseAttRelAttack;                    // Attack time in ms.
    FLOAT32 snrSmoothingHoldTimeMsDef;            // SNR smoothing hold time default in ms.
    FLOAT32 snrSmoothingHoldTimeMsMaxDev;         // SNR smoothing hold time max deviation in ms.
    FLOAT32 snrSmoothingReleaseTimeMsDef;         // SNR smoothing release time default in ms.
    FLOAT32 snrSmoothingReleaseTimeMsMaxDev;      // SNR smoothing release time max deviation in ms.
    FLOAT32 signalPathSmoothingHz;                // Estimation-path smoothing low-pass-filter cutoff-frequency in Hz.
    FLOAT32 noiseSmoothStartFreq;                 // Start frequency for cross-bin smoothing.
    FLOAT32 snrThreshdB;                          // SNR threshold in dB.
    FLOAT32 snrThreshdBDef;                       // SNR threshold default in dB.
    FLOAT32 snrThreshdBMaxDev;                    // SNR threshold max deviation in dB.
    FLOAT32 alphaAttackTimeMsDef;                 // Alpha up (raw) attack time default in ms.
    FLOAT32 alphaAttackTimeMsMaxDev;              // Alpha up (raw) attack time max deviation in ms.
    FLOAT32 logisticOffset;                       // Logistic function offset.
    FLOAT32 logisticSlope;                        // Logistic function gain.
    FLOAT32 alphaReleaseTimeMs;                   // Alpha down release time in ms.
    FLOAT32 noiseLevelInitdB;                     // Initial noise level state in dB.
    INT32* aCtrlValues;                           // Array with ctrl signal values.
    FLOAT32* aSnrCtrlAttRelEnvState;              // Attack-release envelope state.
    FLOAT32* aSnrCtrlAttRelHoldState;             // Attack-release hold state.
    FLOAT32* aSnrCtrlAttRelFb;                    // Attack-release output feedback.
    FLOAT32* aSnrNoiseTrackFb;                    // Control-path noise-tracking feedback.
    FLOAT32* aSnrNoiseLevelFb;                    // Control-path noise-level feedback.
    FLOAT32* aSnrAdjustAttRelEnvState;            // Attack-release envelope state.
    FLOAT32* aSnrAdjustAttRelHoldState;           // Attack-release hold state.
    FLOAT32* aSnrAdjustAttRel2EnvState;           // Attack-release envelope state.
    FLOAT32* aSnrAdjustAttRel2HoldState;          // Attack-release hold state.
    FLOAT32* aSnrAttRelEnvState;                  // Attack-release envelope state.
    FLOAT32* aSnrAttRelHoldState;                 // Attack-release hold state.
    INT32* aSnrSmoothStartIdx;                    // Starting index for the averaging process.
    INT32* aSnrSmoothEndIdx;                      // Ending index for the averaging process.
    FLOAT32* aSnrSmoothOneOverN;                  // Precomputed 1/N for averaging.
    FLOAT32* aNoiseAttRelEnvState;                // Attack-release envelope state.
    FLOAT32* aNoiseAttRelHoldState;               // Attack-release hold state.
    FLOAT32* aNoiseSofState;                      // SOF first state.
    INT32* aNoiseSmoothStartIdx;                  // Starting index for the averaging process.
    INT32* aNoiseSmoothEndIdx;                    // Ending index for the averaging process.
    FLOAT32* aNoiseSmoothOneOverN;                // Precomputed 1/N for averaging.
    FLOAT32* aAraFb;                              // ARA feedback line.
} ModuleNoiseTrackingClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
snrCtrlAttRelHoldCount	int	derived	0	48	Unrestricted
snrCtrlAttRelAttCoeff	float	derived	0	1.7881e-07	Unrestricted
snrCtrlAttRelRelCoeff	float	derived	0	0.010363	Unrestricted
snrAdjustAttRelHoldCount	int	derived	0	4800	Unrestricted
snrAdjustAttRelAttCoeff	float	derived	0	1	Unrestricted
snrAdjustAttRelRelCoeff	float	derived	0	4.1664e-05	Unrestricted
snrAdjustAttRel2HoldCount	int	derived	0	4800	Unrestricted
snrAdjustAttRel2AttCoeff	float	derived	0	1	Unrestricted
snrAdjustAttRel2RelCoeff	float	derived	0	2.0862e-06	Unrestricted
snrAdjustScaleOffOffset	float	derived	0	1	Unrestricted
snrAttRelHoldCount	int	derived	0	480	Unrestricted
snrAttRelAttCoeff	float	derived	0	1	Unrestricted
snrAttRelRelCoeff	float	derived	0	0.0020812	Unrestricted
snrScaleOff1Offset	float	derived	0	1	Unrestricted
snrScaleOff2Offset	float	derived	0	-0.0020833	Unrestricted
noiseAttRelHoldCount	int	derived	0	1	Unrestricted
noiseAttRelAttCoeff	float	derived	0	1	Unrestricted
noiseAttRelRelCoeff	float	derived	0	0	Unrestricted
noiseSofB0	float	derived	0	0.00098079	Unrestricted
noiseSofB1	float	derived	0	0.00098079	Unrestricted
noiseSofA1	float	derived	0	0.99804	Unrestricted
noiseAdjustdB	float	parameter	0	6	-24:24	dB
noiseScaleOffGain	float	derived	0	1	Unrestricted
noiseSmoothOctave	float	parameter	0	0.1	0:1
araAlphaCalcUpScaleOff2Offset	float	derived	0	1	Unrestricted
araScaleOffOffset	float	derived	0	0.99979	Unrestricted
noiseFloordB	float	parameter	0	-120	-150:0	dB
noiseFloorLinear	float	derived	0	1	Unrestricted
trackingSpeed	float	parameter	0	1	0:2
sensitivity	float	parameter	0	1	0:2
enableControlInputs	int	const	1	0	Unrestricted
snrCtrlAttRelAttack	float	const	1	100000	Unrestricted
snrCtrlAttRelRelease	float	const	1	2	Unrestricted
snrCtrlAttRelHold	float	const	1	1	Unrestricted
snrAdjustAttRelAttack	float	const	1	0	Unrestricted
snrAdjustAttRelRelease	float	const	1	500	Unrestricted
snrAdjustAttRelHold	float	const	1	100	Unrestricted
snrAdjustAttRel2Attack	float	const	1	0	Unrestricted
snrAdjustAttRel2Release	float	const	1	10000	Unrestricted
snrAdjustAttRel2Hold	float	const	1	100	Unrestricted
snrAdjustThreshdB	float	const	1	10	Unrestricted
snrAdjustClipAsymUpper	float	const	1	10	Unrestricted
snrAttRelAttack	float	const	1	0	Unrestricted
snrAttRelRelease	float	const	1	10	Unrestricted
snrAttRelHold	float	const	1	10	Unrestricted
noiseSmoothWidth	float	const	1	0.25	Unrestricted
snrSmoothStartFreq	float	const	1	0	Unrestricted
noiseStepUpdBDef	float	const	1	20	Unrestricted
noiseStepUpdBMaxDev	float	const	1	10	Unrestricted
noiseStepDowndB	float	const	1	-100	Unrestricted
noiseAttRelAttack	float	const	1	0	Unrestricted
snrSmoothingHoldTimeMsDef	float	const	1	100	Unrestricted
snrSmoothingHoldTimeMsMaxDev	float	const	1	100	Unrestricted
snrSmoothingReleaseTimeMsDef	float	const	1	800	Unrestricted
snrSmoothingReleaseTimeMsMaxDev	float	const	1	500	Unrestricted
signalPathSmoothingHz	float	const	1	15	Unrestricted
noiseSmoothStartFreq	float	const	1	0	Unrestricted
snrThreshdB	float	derived	1	1	Unrestricted
snrThreshdBDef	float	const	1	30	Unrestricted
snrThreshdBMaxDev	float	const	1	5	Unrestricted
alphaAttackTimeMsDef	float	const	1	1700	Unrestricted
alphaAttackTimeMsMaxDev	float	const	1	1000	Unrestricted
logisticOffset	float	const	1	0	Unrestricted
logisticSlope	float	const	1	100	Unrestricted
alphaReleaseTimeMs	float	const	1	100	Unrestricted
noiseLevelInitdB	float	const	1	-50	Unrestricted
aCtrlValues	int*	state	1	[1 x 32]	Unrestricted
aSnrCtrlAttRelEnvState	float*	state	1	[1 x 32]	Unrestricted
aSnrCtrlAttRelHoldState	float*	state	1	[1 x 32]	Unrestricted
aSnrCtrlAttRelFb	float*	state	1	[1 x 32]	Unrestricted
aSnrNoiseTrackFb	float*	state	1	[1 x 32]	Unrestricted
aSnrNoiseLevelFb	float*	state	1	[1 x 32]	Unrestricted
aSnrAdjustAttRelEnvState	float*	state	1	[1 x 32]	Unrestricted
aSnrAdjustAttRelHoldState	float*	state	1	[1 x 32]	Unrestricted
aSnrAdjustAttRel2EnvState	float*	state	1	[1 x 32]	Unrestricted
aSnrAdjustAttRel2HoldState	float*	state	1	[1 x 32]	Unrestricted
aSnrAttRelEnvState	float*	state	1	[1 x 32]	Unrestricted
aSnrAttRelHoldState	float*	state	1	[1 x 32]	Unrestricted
aSnrSmoothStartIdx	int*	state	1	[32 x 1]	Unrestricted
aSnrSmoothEndIdx	int*	state	1	[32 x 1]	Unrestricted
aSnrSmoothOneOverN	float*	state	1	[32 x 1]	Unrestricted
aNoiseAttRelEnvState	float*	state	1	[1 x 32]	Unrestricted
aNoiseAttRelHoldState	float*	state	1	[1 x 32]	Unrestricted
aNoiseSofState	float*	state	1	[1 x 32]	Unrestricted
aNoiseSmoothStartIdx	int*	derived	1	[32 x 1]	Unrestricted
aNoiseSmoothEndIdx	int*	derived	1	[32 x 1]	Unrestricted
aNoiseSmoothOneOverN	float*	derived	1	[32 x 1]	Unrestricted
aAraFb	float*	state	1	[1 x 32]	Unrestricted

Pins

Input Pins

Name: sig

Description: Audio inputs

Data type: float

Channel range: 1

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: Output signal

Data type: float

Scratch Pins

Channel count: 1

Block size: 33

Sample rate: 48000

Channel count: 1

Block size: 32

Sample rate: 48000

MATLAB Usage

File Name: noise_tracking_module.m

 M = noise_tracking_module(NAME)
 Single-channel stationary-noise tracker. This module estimates
 stationary-noise levels per subband.
 Arguments:
 NAME - name of the module.
 CTRL_PINS_ENABLE - creates pins for up-down-tracking control.
 NOISE_LEVEL_INIT - sets initial noise-level estimate.