HIWIRE MEETING Athens, November 3-4, 2005

HIWIRE MEETINGHIWIRE MEETINGAthens, November 3-4, 2005Athens, November 3-4, 2005

José C. Segura, Ángel de la TorreJosé C. Segura, Ángel de la Torre

2 HIWIRE Meeting – Athens, 3 - 4 November, 2005

Schedule

HIWIRE database evaluations

Non-linear feature normalization ECDF segmental implementation Parametric equalization

Robust VAD Bispectrum-based VAD

Model-based feature compensation VTS results on AURORA4 Including uncertainty caused by noise



PARAMETERS: MFCC_0_D_A_Z (39 component)

MODELS: TIMIT: 46 phone models / 3 states / 128 Gaussians (17.664 G) WSJ16k: 16.825 triphones / 3.608 tied-states / 6 Gaussians (21.648 G) WSJ16kFon: 40 phone models / 3 states / 128 Gaussians (15.360 G)

ADAPTATION: MLLR: 32 regression classes / 50 adaptation utterances

GRAMMAR: LORIA & Word-Loop MODIFICATIONS: Some transcriptions have been modified to match

the grammar definition


Transcription modifications

BEGIN { lista = LISTA; nfrase = 0;}

{ linea=$0; gsub("-","_",linea); gsub("Due_to_","Due_to ",linea); gsub("Mayday_Mayday","Mayday Mayday",linea); gsub("Pan_Pan","Pan Pan",linea); gsub("three hundred twenty","three_hundred_twenty",linea); gsub("one hundred sixty","one_hundred_sixty",linea); printf("%s\n",tolower(linea)); nfrase = nfrase+1;}


HIWIRE database results

MODELS French Greek Italian Spanish World AvgTIMIT 7,30 9,93 11,87 9,27 6,26 8,93WSJ16k 14,70 25,11 20,66 18,01 14,32 18,56WSJ16kFon 10,43 19,51 16,52 15,33 8,72 14,10TIMIT_WL 26,79 33,77 35,61 30,88 22,53 29,92

RESULTS WITHOUT ADAPTATION (WER)

MODELS French Greek Italian Spanish World AvgTIMIT+MLLR 3,13 2,51 3,80 2,99 3,16 3,12WSJ16k+MLLR 3,85 4,48 5,94 4,53 4,00 4,56WSJ16kFon+MLLR 3,50 2,98 7,00 5,55 3,94 4,59TIMIT_WL+MLLR 11,12 9,43 14,61 13,14 12,20 12,10

RESULTS WITH MLLR (WER)


Schedule


Non-linear feature normalization ECDF segmental implementation Parametric equalization




ECDF segmental implementation

ECDF segmental implementation

Provided LOQUENDO with a reference “C” implementation of segmental Gaussian transformation to be tested within LOQUENDO recognizer

Current work Nonlinear feature transformation with a clean reference to

avoid the problem of system retraining


HEQ limitations

Influence of relative amount of silence in utterances

With a parametric model, a more robust equalization can be obtained

Parametric Equalization (1)

PARAMETRIC NONLINEAR FEATURE EQUALIZATIONFOR ROBUST SPEECH RECOGNITION (submitted ICASSP’06)



CLASS-DEPENDENT LINEAR EQUALIZATION

SOFT DECISSION VAD (two-class Gaussian classifier on C0)NONLINEAR INTERPOLATION





In comparison with HEQ, PEQ transformations are smoother

For C0 a monotonic transformation is obtained

For other coefficients, the interpolated transformation is not monotonic



BASE MFCC_0_D_A_Z (39 component)

HEQ Quantile based CDF-transformation Clean reference Implemented over MFCC_0 / CMS and regressions computed after HEQ

AFE Standard implementation

PEQ Clean reference Implemented over MFCC_0 / CMS and regressions computed after PEQ



Current work

Development of an on-line version

Relax the diagonal covariance assumption

Investigate the normalization of dynamic features

Using a more detailed model of speech frames (i.e. More than one Gaussian)


Schedule


Non-linear feature normalization ECDF segmental implementation (LOQ) Parametric equalization




Bispectrum-based VAD (1)

Motivations: Ability of higher order statistics to detect signals in noise Polyspectra methods rely on an a priori knowledge of the input

processes

Issues to be addressed: Computationally expensive Variance of the bispectrum estimators is much higher than that of

power spectral estimators for identical data record size

Solution: Integrated bispectrum J. K. Tugnait, “Detection of non-Gaussian signals using integrated

polyspectrum,” IEEE Trans. on Signal Processing, vol. 42, no. 11, pp. 3137–3149, 1994.

Computationally efficient and reduced variance statistical test based on the integrated polyspectra

Detection of an unknown random, stationary, non-Gaussian signal in Gaussian noise



Integrated bispectrum: Defined as a cross spectrum between the signal and its square,

and therefore, it is a function of a single frequency variable

Benefits: Its computation as a cross spectrum leads to significant

computational savings

The variance of the estimator is of the same order as that of the power spectrum estimator

Properties Bispectrum of a Gaussian process is identically zero, its integrated

bispectrum is as well


Two alternatives explored for formulating the decision rule: Estimation by block averaging:

MO-LRT Given a set of N= 2m+1 consecutive observations:


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Likelihoods

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Bispectrum-based VAD results (1)

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Schedule


Non-linear feature normalization ECDF segmental implementation (LOQ) Parametric equalization




Schedule

Model-based feature compensation VTS: results on AURORA4

VTS formulation VTS vs non linear feature normalization procedures VTS results on AURORA 4

Including uncertainty caused by noise Including uncertainty in noise compensation Wiener filtering + uncertainty: results on Aurora 2 Wiener filtering + uncertainty: results on Aurora 4 VTS + uncertainty: formulation Numerical integration of probabilities: formulation


VTS formulation

VTS: Vector Taylor Series approach to remove additive (and channel) noise

References: P.J. Moreno. “Speech recognition in noisy environments” Ph.D.

Thesis, Carnegie-Mellon University, Pittsburgh, Pensilvania, Apr. 1996.

A. de la Torre. “Técnicas de mejora de la representación en los sistemas de reconocimiento automático del habla” Ph.D. Thesis, University of Granada, Spain, Apr. 1999.


VTS formulation

VTS provides an estimation of the clean speech in a statistical framework:

Log-FBO domain, assumed additive noise:

Effect of noise described using the “correction function” g():


Auxiliary functions f() and h(): 1st and 2nd derivatives:

VTS provides estimation of noisy-speech Gaussian given the clean-speech and the noise Gaussians:

Noisy-speech Gaussian obtained with the expected values:

VTS formulation


VTS formulation

Noisy-speech Gaussian: formulas:

Models for noise and clean speech:


VTS formulation

Model for clean speech provides the model for noisy speech, and also P(k|y) (posterior probability of each Gaussian):

Estimation of clean speech:


VTS vs non-linear feature normalization

VTS: Statistical framework: Model for noise in log-FBO domain: 1 Gaussian PDF Model for clean-speech in log-FBO domain: Gaussian mixture Noise assumed to be additive in FBO domain Accurate description of noise process

ACCURATE COMPENSATION

Non-linear feature normalization: No a-priori assumption Component-by-component

MORE FLEXIBLE, LESS ACCURATE


VTS results on AURORA 4

Experiment Train mode

Test size

WER exp. 01-07

WER exp. 08-14

WER exp. 01-14

Baseline Clean 166 40.53 % 50.60 % 45.57 %

HEQ Clean 166 32.19 % 42.74 % 37.47 %

Parametric non-linear EQ

Clean 166 28.78 % 34.27 % 31.53 %

VTS Clean 166 29.46 % 37.22 % 33.34 %

VTS (noise known)

Clean 166 26.97 % 32.25 % 26.97 %

AFE Clean 166 27.57 % 34.99 % 31.28 %

Baseline Multi 166 24.58 % 29.88 % 27.23 %


Including uncertainty in noise compensation

Noise is a random process: we do not know n, but p(n)

Then, from an observation y we cannot find x, but p(x|y,x,n)

Usually, compensation procedures provide E[x|y,x,n]

What about uncertainty of x ?

Mean and variance of x :





An approach for the estimation of the variance:

Evaluation of HMM Gaussians:


Wiener filt. + uncertainty: results on AURORA 2

Preliminary results with Wiener filtering:

Results on Aurora 2 with Wiener filtering + uncertainty

Train mode WER Set A WER Set B WER Set C Aver. WER

Wiener Clean 15.75 % 15.87 % 17.62 % 16.17 %

Wiener + Uncert. Clean 12.13 % 12.90 % 13.28 % 12.67 %

Wiener Multi 8.91 % 10.44 % 10.95 % 9.93 %

Wiener + Uncert. Multi 8.87 % 10.34 % 10.69 % 9.82 %


Wiener filter + uncertainty: results on AURORA 4

Experiment Train mode

Test size

WER exp. 01-07

WER exp. 08-14

WER exp. 01-14

Baseline Clean 166 40.53 % 50.60 % 45.57 %

HEQ Clean 166 32.19 % 42.74 % 37.47 %

Parametric non-linear EQ

Clean 166 28.78 % 34.27 % 31.53 %

VTS Clean 166 29.46 % 37.22 % 33.34 %

Wiener + Uncertainty

Clean 166 27.68 % 33.79 % 30.74 %

AFE Clean 166 27.57 % 34.99 % 31.28 %

Baseline Multi 166 24.58 % 29.88 % 27.23 %


VTS + uncertainty: formulation

VTS based estimation of clean speech:

VTS based estimation of variance:


Numerical integration of probabilities: formulation

Computation of expected values:

Numerical integration of expected values:

HIWIRE MEETINGHIWIRE MEETINGAthens, November 3-4, 2005Athens, November 3-4, 2005

José C. Segura, Ángel de la TorreJosé C. Segura, Ángel de la Torre

Documents

HIWIRE MEETING Athens, November 3-4, 2005