Jiao Tong University Research Asia 3 National Cheng Kung University 2 Microsoft

(Development in ICASSP conference, 2009)

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Outline

Motivation Evidence Framework CDHMMs with VB Experiment

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Outline

Motivation Evidence Framework CDHMMs with VB Experiment

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Motivation

Robust acoustic modeling is critical when collected training data is sparse, noisy and mismatched with test. Hidden Markov Models is the most commonly acoustic models. But the ill-posed conditions severely may hamper the trained HMMs to recognize test data robustly. In an evidence Bayesian framework, we can build a better regularized HMM with given finite data, hence more robust recognition performance.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Motivation

Robust acoustic modeling is critical when collected training data is sparse, noisy and mismatched with test. Hidden Markov Models is the most commonly acoustic models. But the ill-posed conditions severely may hamper the trained HMMs to recognize test data robustly. In an evidence Bayesian framework, we can build a better regularized HMM with given finite data, hence more robust recognition performance.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Motivation

Robust acoustic modeling is critical when collected training data is sparse, noisy and mismatched with test. Hidden Markov Models is the most commonly acoustic models. But the ill-posed conditions severely may hamper the trained HMMs to recognize test data robustly. In an evidence Bayesian framework, we can build a better regularized HMM with given finite data, hence more robust recognition performance.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Motivation

Robust acoustic modeling is critical when collected training data is sparse, noisy and mismatched with test. Hidden Markov Models is the most commonly acoustic models. But the ill-posed conditions severely may hamper the trained HMMs to recognize test data robustly. In an evidence Bayesian framework, we can build a better regularized HMM with given finite data, hence more robust recognition performance.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

In this paper, we √

Apply evidence framework to exponential family √ distribution estimation. Extend it to estimating CDHMMs with naturally built-in model uncertainty.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

In this paper, we √

Apply evidence framework to exponential family √ distribution estimation. Extend it to estimating CDHMMs with naturally built-in model uncertainty.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

In this paper, we √

Apply evidence framework to exponential family √ distribution estimation. Extend it to estimating CDHMMs with naturally built-in model uncertainty.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Outline

Motivation Evidence Framework CDHMMs with VB Experiment

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Evidence Framework Notations η: hyper-parameter of the model {λi }: distribution parameters {Di }: set of training data

Model Evidence as the Objective Function ˆ = arg max p(D1 , . . . , DK |η) η η

= arg max η

K Z Y i=1

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

p(Di |λi )p(λi |η)dλi

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Evidence Framework Notations η: hyper-parameter of the model {λi }: distribution parameters {Di }: set of training data

Model Evidence as the Objective Function ˆ = arg max p(D1 , . . . , DK |η) η η

= arg max η

K Z Y i=1

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

p(Di |λi )p(λi |η)dλi

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Evidence Framework Notations η: hyper-parameter of the model {λi }: distribution parameters {Di }: set of training data

Model Evidence as the Objective Function ˆ = arg max p(D1 , . . . , DK |η) η η

= arg max η

K Z Y i=1

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

p(Di |λi )p(λi |η)dλi

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Evidence Framework Notations η: hyper-parameter of the model {λi }: distribution parameters {Di }: set of training data

Model Evidence as the Objective Function ˆ = arg max p(D1 , . . . , DK |η) η η

= arg max η

K Z Y i=1

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

p(Di |λi )p(λi |η)dλi

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Evidence Framework Notations η: hyper-parameter of the model {λi }: distribution parameters {Di }: set of training data

Model Evidence as the Objective Function ˆ = arg max p(D1 , . . . , DK |η) η η

= arg max η

K Z Y i=1

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

p(Di |λi )p(λi |η)dλi

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Solution

Key idea: treat λi as hidden variable. E-Step: Q(η, η

old

)=

K Z X i=1

p(λi |Di , η old ) ln p(Di , λi |η)dλi

M-Step: obtain the solution of all models in the exponential family.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Solution

Key idea: treat λi as hidden variable. E-Step: Q(η, η

old

)=

K Z X i=1

p(λi |Di , η old ) ln p(Di , λi |η)dλi

M-Step: obtain the solution of all models in the exponential family.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Solution

Key idea: treat λi as hidden variable. E-Step: Q(η, η

old

)=

K Z X i=1

p(λi |Di , η old ) ln p(Di , λi |η)dλi

M-Step: obtain the solution of all models in the exponential family.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Fundamentals of Exponential Family Distributions Exponential Family p(xi |λi ) = h(xi )g(λi ) exp[λ⊤ i u(xi )] Sufficient statistics X

u(x)

x∈D

Conjugate prior p(λi |χ0 , ν0 ) = f (χ0 , ν0 )g(λi )ν0 exp(ν0 λ⊤ i χ0 )

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Fundamentals of Exponential Family Distributions Exponential Family p(xi |λi ) = h(xi )g(λi ) exp[λ⊤ i u(xi )] Sufficient statistics X

u(x)

x∈D

Conjugate prior p(λi |χ0 , ν0 ) = f (χ0 , ν0 )g(λi )ν0 exp(ν0 λ⊤ i χ0 )

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Fundamentals of Exponential Family Distributions Exponential Family p(xi |λi ) = h(xi )g(λi ) exp[λ⊤ i u(xi )] Sufficient statistics X

u(x)

x∈D

Conjugate prior p(λi |χ0 , ν0 ) = f (χ0 , ν0 )g(λi )ν0 exp(ν0 λ⊤ i χ0 )

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family Note that the Graphical Model Hyper-parameters η

Model Parameters λ1

λ2

λK

Data Set D1

D2

DK

Graph.00 Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family Note that the Graphical Model Hyper-parameters η

Model Parameters λ1

λ2

λK

Data Set D1

D2

DK

Graph.01 Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family Note that the Graphical Model Hyper-parameters η

Model Parameters λ1

λ2

λK

Data Set D1

D2

DK

Graph.02 Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family Note that the Graphical Model Preceding node η

Given parents node λ1

λ2

Succeeding node D1

D2

λK

DK Graph.03

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Independent

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family

Using the two properties With conjugate prior, the posterior can have the same functional form as its prior. Di is conditionally independent of ηi , given λi (Di ⊥ηi |λi ). we get ⇒ Q(η, ηold ) =

K Z X i=1

p(λi |˜ η old i ) ln p(λi |η)dλi + C

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family

Using the two properties With conjugate prior, the posterior can have the same functional form as its prior. Di is conditionally independent of ηi , given λi (Di ⊥ηi |λi ). we get ⇒ Q(η, ηold ) =

K Z X i=1

p(λi |˜ η old i ) ln p(λi |η)dλi + C

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family

Using the two properties With conjugate prior, the posterior can have the same functional form as its prior. Di is conditionally independent of ηi , given λi (Di ⊥ηi |λi ). we get ⇒ Q(η, ηold ) =

K Z X i=1

p(λi |˜ η old i ) ln p(λi |η)dλi + C

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family

Using the two properties With conjugate prior, the posterior can have the same functional form as its prior. Di is conditionally independent of ηi , given λi (Di ⊥ηi |λi ). we get ⇒ Q(η, ηold ) =

K Z X i=1

p(λi |˜ η old i ) ln p(λi |η)dλi + C

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family E-step ν˜i = ν + γi Pγi n=1 u(xi,n ) + νχ ˜i = χ ν˜i M-step hλ, ln[g(λ)]iηnew =

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

K 1 X hλ, ln[g(λ)]iη˜ old i K i=1

Outline Motivation Evidence Framework CDHMMs with VB Experiment

EM Empirical Bayesian Learning for the Exponential Family E-step ν˜i = ν + γi Pγi n=1 u(xi,n ) + νχ ˜i = χ ν˜i M-step hλ, ln[g(λ)]iηnew =

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

K 1 X hλ, ln[g(λ)]iη˜ old i K i=1

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Concavity Analysis

The auxiliary function Q(η, η old ) is concave ⇒ we can obtain its global optimum in the M-step. In general, the objective function F (the evidence) is not concave. F(η) = p(D1 , . . . , DK |η) P Good news: ∇2 F is proportional to i {cov η˜ i − covη } (Note: posterior is usually sharper than its prior)

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Concavity Analysis

The auxiliary function Q(η, η old ) is concave ⇒ we can obtain its global optimum in the M-step. In general, the objective function F (the evidence) is not concave. F(η) = p(D1 , . . . , DK |η) P Good news: ∇2 F is proportional to i {cov η˜ i − covη } (Note: posterior is usually sharper than its prior)

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Concavity Analysis

The auxiliary function Q(η, η old ) is concave ⇒ we can obtain its global optimum in the M-step. In general, the objective function F (the evidence) is not concave. F(η) = p(D1 , . . . , DK |η) P Good news: ∇2 F is proportional to i {cov η˜ i − covη } (Note: posterior is usually sharper than its prior)

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Outline

Motivation Evidence Framework CDHMMs with VB Experiment

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

An Introduction of Approximated Inference

In some cases, we could hardly evaluate this joint posterior distribution of hidden variables. For example, when training Bayesian HMMs empirically, we need to evaluate p(λ, s|D) in the E-Step. where λ is the HMM parameters and s is the state sequence.

Probabilistic Approach: Monte-Carlo, theoretically good but computationally infeasible. Deterministic Approach: Select a proper q(λ, s) to approximate p(λ, s|D).

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

An Introduction of Approximated Inference

In some cases, we could hardly evaluate this joint posterior distribution of hidden variables. For example, when training Bayesian HMMs empirically, we need to evaluate p(λ, s|D) in the E-Step. where λ is the HMM parameters and s is the state sequence.

Probabilistic Approach: Monte-Carlo, theoretically good but computationally infeasible. Deterministic Approach: Select a proper q(λ, s) to approximate p(λ, s|D).

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

An Introduction of Approximated Inference

In some cases, we could hardly evaluate this joint posterior distribution of hidden variables. For example, when training Bayesian HMMs empirically, we need to evaluate p(λ, s|D) in the E-Step. where λ is the HMM parameters and s is the state sequence.

Probabilistic Approach: Monte-Carlo, theoretically good but computationally infeasible. Deterministic Approach: Select a proper q(λ, s) to approximate p(λ, s|D).

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

An Introduction of Approximated Inference

In some cases, we could hardly evaluate this joint posterior distribution of hidden variables. For example, when training Bayesian HMMs empirically, we need to evaluate p(λ, s|D) in the E-Step. where λ is the HMM parameters and s is the state sequence.

Probabilistic Approach: Monte-Carlo, theoretically good but computationally infeasible. Deterministic Approach: Select a proper q(λ, s) to approximate p(λ, s|D).

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

An Introduction of Approximated Inference

In some cases, we could hardly evaluate this joint posterior distribution of hidden variables. For example, when training Bayesian HMMs empirically, we need to evaluate p(λ, s|D) in the E-Step. where λ is the HMM parameters and s is the state sequence.

Probabilistic Approach: Monte-Carlo, theoretically good but computationally infeasible. Deterministic Approach: Select a proper q(λ, s) to approximate p(λ, s|D).

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Variational Approach Separability assumption: q(λ, s) = q(λ)q(s). We can get a new lower bound on model log marginal likelihood Z p(λ, s, D|m) Fm (q(λ), q(s)) = q(λ)q(s) ln q(λ)q(s) It can be iteratively optimized q new (λ) ∝ exp < ln p(D, s|λ) >qold (s) q new (s) ∝ exp < ln p(D, s|λ) >qold (λ)

We have the closed form solution for q new (λ), q new (s) in CDHMM case. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Variational Approach Separability assumption: q(λ, s) = q(λ)q(s). We can get a new lower bound on model log marginal likelihood Z p(λ, s, D|m) Fm (q(λ), q(s)) = q(λ)q(s) ln q(λ)q(s) It can be iteratively optimized q new (λ) ∝ exp < ln p(D, s|λ) >qold (s) q new (s) ∝ exp < ln p(D, s|λ) >qold (λ)

We have the closed form solution for q new (λ), q new (s) in CDHMM case. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Variational Approach Separability assumption: q(λ, s) = q(λ)q(s). We can get a new lower bound on model log marginal likelihood Z p(λ, s, D|m) Fm (q(λ), q(s)) = q(λ)q(s) ln q(λ)q(s) It can be iteratively optimized q new (λ) ∝ exp < ln p(D, s|λ) >qold (s) q new (s) ∝ exp < ln p(D, s|λ) >qold (λ)

We have the closed form solution for q new (λ), q new (s) in CDHMM case. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Variational Approach Separability assumption: q(λ, s) = q(λ)q(s). We can get a new lower bound on model log marginal likelihood Z p(λ, s, D|m) Fm (q(λ), q(s)) = q(λ)q(s) ln q(λ)q(s) It can be iteratively optimized q new (λ) ∝ exp < ln p(D, s|λ) >qold (s) q new (s) ∝ exp < ln p(D, s|λ) >qold (λ)

We have the closed form solution for q new (λ), q new (s) in CDHMM case. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Variational Approach Separability assumption: q(λ, s) = q(λ)q(s). We can get a new lower bound on model log marginal likelihood Z p(λ, s, D|m) Fm (q(λ), q(s)) = q(λ)q(s) ln q(λ)q(s) It can be iteratively optimized q new (λ) ∝ exp < ln p(D, s|λ) >qold (s) q new (s) ∝ exp < ln p(D, s|λ) >qold (λ)

We have the closed form solution for q new (λ), q new (s) in CDHMM case. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

The Pseudo Code of Evidence Framework based Bayesian Training for CDHMMs iteration loop: variational E-step: conduct Baum-welch on the training set, by using expected log likelihoods instead of Gaussian probabilities, and collect statistics, γi , γi (o), γi (oo⊤ ) variational M-step: maximum evidence E-step: calculate η ˜old for all the CDHMM parameters i maximum evidence M-step: solve η new with the expectation equation while the evidence gap is larger than a threshold Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Optimization Procedure

Log Marginal likelihood Log Marginal likelihood

Log Marginal likelihood

KL(q ||p) KL(q ||p)

VBEM Step

KL(q ||p)

Hyper-parameter estimate New lower bound

New lower bound maximum evidence EM

Lower bound

VB Baum-Welch

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Parameters Update Gaussian Parameters Conjugate prior is Gaussian-Wishart p(µi , Λi |η) = N (µi ; µ0 , β0−1 Λ−1 i )W(Λi ; Λ0 , ν0 )

Weight Parameters Conjugate prior is Dirichlet distribution p(ωi1 , . . . , ωiM |α01 , . . . , α0M ) =

See more detail in my paper. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

M Y

m=1

α0m −1 ωim

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Parameters Update Gaussian Parameters Conjugate prior is Gaussian-Wishart p(µi , Λi |η) = N (µi ; µ0 , β0−1 Λ−1 i )W(Λi ; Λ0 , ν0 )

Weight Parameters Conjugate prior is Dirichlet distribution p(ωi1 , . . . , ωiM |α01 , . . . , α0M ) =

See more detail in my paper. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

M Y

m=1

α0m −1 ωim

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Parameters Update Gaussian Parameters Conjugate prior is Gaussian-Wishart p(µi , Λi |η) = N (µi ; µ0 , β0−1 Λ−1 i )W(Λi ; Λ0 , ν0 )

Weight Parameters Conjugate prior is Dirichlet distribution p(ωi1 , . . . , ωiM |α01 , . . . , α0M ) =

See more detail in my paper. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

M Y

m=1

α0m −1 ωim

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Parameters Update Gaussian Parameters Conjugate prior is Gaussian-Wishart p(µi , Λi |η) = N (µi ; µ0 , β0−1 Λ−1 i )W(Λi ; Λ0 , ν0 )

Weight Parameters Conjugate prior is Dirichlet distribution p(ωi1 , . . . , ωiM |α01 , . . . , α0M ) =

See more detail in my paper. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

M Y

m=1

α0m −1 ωim

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Parameters Update Gaussian Parameters Conjugate prior is Gaussian-Wishart p(µi , Λi |η) = N (µi ; µ0 , β0−1 Λ−1 i )W(Λi ; Λ0 , ν0 )

Weight Parameters Conjugate prior is Dirichlet distribution p(ωi1 , . . . , ωiM |α01 , . . . , α0M ) =

See more detail in my paper. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

M Y

m=1

α0m −1 ωim

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Outline

Motivation Evidence Framework CDHMMs with VB Experiment

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experiments The evidence framework of CDHMMs was tested on Aurora2, a connected digit recognition task. Whole-word HMM Eleven digits, from ’zero’ to ’nine’, plus ’oh’. 3-component GMM for each the states. Diagonal covariance matrices.

Training Different sized clean training Different sized multi-conditioned training.

Test 0dB-20dB test data. We compared the average word accuracy on the testing. Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Bayesian Predictive Classifier

˜ = argmaxs Bayesian Prediction s

R

p(oT |λs )p(λs |D)dλs

Usually, p(λs |D) is the trained posterior distribution and used as the prior distribution in testing. Used in this study frame-based approximation (used in this study) Assume the prior to be independent for each frame. We have a Student-t, instead of Gaussian, distribution.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Bayesian Predictive Classifier

˜ = argmaxs Bayesian Prediction s

R

p(oT |λs )p(λs |D)dλs

Usually, p(λs |D) is the trained posterior distribution and used as the prior distribution in testing. Used in this study frame-based approximation (used in this study) Assume the prior to be independent for each frame. We have a Student-t, instead of Gaussian, distribution.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Bayesian Predictive Classifier

˜ = argmaxs Bayesian Prediction s

R

p(oT |λs )p(λs |D)dλs

Usually, p(λs |D) is the trained posterior distribution and used as the prior distribution in testing. Used in this study frame-based approximation (used in this study) Assume the prior to be independent for each frame. We have a Student-t, instead of Gaussian, distribution.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Bayesian Predictive Classifier

˜ = argmaxs Bayesian Prediction s

R

p(oT |λs )p(λs |D)dλs

Usually, p(λs |D) is the trained posterior distribution and used as the prior distribution in testing. Used in this study frame-based approximation (used in this study) Assume the prior to be independent for each frame. We have a Student-t, instead of Gaussian, distribution.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Bayesian Predictive Classifier

˜ = argmaxs Bayesian Prediction s

R

p(oT |λs )p(λs |D)dλs

Usually, p(λs |D) is the trained posterior distribution and used as the prior distribution in testing. Used in this study frame-based approximation (used in this study) Assume the prior to be independent for each frame. We have a Student-t, instead of Gaussian, distribution.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Experimental Results 70

90

65

85

60 80 word accuracy(%)

word accuracy(%)

55 50 45 40 evidence β0 = ν0 = 2 (best)

35 30

75 70 65 evidence β = ν =2

60

0

0

0

β = ν = 0.1

25

0

0

3

10 # training utterance

0

β0 = ν0 = 0.1 (best)

55

0

ML

ML 20 2 10

0

β = ν = 0.5

β = ν = 0.5

50 2 10

3

10 # training utterance

Figure: Recognition accuracy of Figure: Recognition accuracy of model trained with different sized model trained with different sized clean training data multi-conditional training data

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Conclusion

We apply the evidence framework, to CDHMM training, which automatically learns the priors and their posteriors from data. The evidence framework trained CDHMM has to better regularization, and higher recognition performance.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Conclusion

We apply the evidence framework, to CDHMM training, which automatically learns the priors and their posteriors from data. The evidence framework trained CDHMM has to better regularization, and higher recognition performance.

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

Outline Motivation Evidence Framework CDHMMs with VB Experiment

Question?

Y.Zhang, P.Liu, J.-T.Chien, F.Soong

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