Dipartimento di Meccanica e Tecnologie Industriali Università degli Studi di Firenze On TFSR...

Dipartimento di Meccanica e Dipartimento di Meccanica e Tecnologie IndustrialiTecnologie Industriali

Università degli Studi di Università degli Studi di FirenzeFirenze

On TFSR (semi)automatic systems On TFSR (semi)automatic systems supportabilitysupportability: : novelnovel instruments for instruments for

analysis and compensationanalysis and compensation

Francesco Borchi, Monica Carfagni, Matteo Nunziati

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OutlineOutline

• Main goal• TFSR Systems • LogR estimation• Common test procedures for TFSR systems• System behaviour classification• Supportability evaluation tools • Score compensation tools• Quality assessment logics• Conclusion

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Main goalMain goal

Our goal is to propose a general purpose set of tools for system compensation and quality assessment

Specific goals:

1. to build a generic framework for system analysis

2. to develop a novel generic tool for system compensation

3. to assess system quality level on the basis of the amount of compensation required by the system itself

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TFSR TFSR SystemSystemss

Voice sample 1

Voice sample 2

TFSR system LogR

We define a TFSR system as a black box which receives two or more recordings as inputs and produces one or more scores (LogR) as outputs

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LLogogR estimationR estimation 1/2 1/2

LogR = log10[P(E | H0) / P( E | H1)]

Log-likelihood ratio defines the most supportable hypotesis

Hypotesis 0: the two samples belong to the same speaker

Hypotesis 1: the two samples belong to different speakers

•If LogR>0 support goes to the H0 hypotesis

•If LogR<0 support goes to the H1 hypotesis

•If LogR=0 no support is provided

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LLogogR estimationR estimation 2/2 2/2

The system goodness depends on a number of factors:

• The way we have used to retrieve voice samples

• The kind of parameters employed in the recognition

• The algorithms used for parameter extraction

• The mathematic model used to estimate LogR

Experimentation is the best way to assess system behaviour

The real LogR value is unknown. We can estimate it using some approximations. Our systems are error-prone.

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Common test procedures for TFSR systemsCommon test procedures for TFSR systems1/21/2

The system is tested against a set of recordings having known origin:

……

Speaker1 …

SpeakerN …

2 or more recordings

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Common test procedures for TFSR systemsCommon test procedures for TFSR systems2/22/2

Recordings are mixed up and grouped in pairs:

Same speaker pairs (SS)

Different speaker pairs (DS)

•SS: test system behaviour when H0 is true. Is LogR>0?

•DS: test system behaviour when H1 is true. Is LogR<0?

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System behaviour classificationSystem behaviour classification1/31/3

Tippett Plot: a common method to show system behaviour

% SS

% DS

False negatives

False positives

H1 H0

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Only false scores

Wrong support

Provide a solution to eliminate “false score only” areas (red boxes)

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•ipoperforming

•isoperforming

Provide a solution to reduce the amount of false scores

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Supportability evaluation tools 1/3Supportability evaluation tools 1/3

A quantitative evaluation of false scores has been proposed byP. Rose et Al. (2003):

LRtest=P(LogR>0 | H0) / P(LogR>0 | H1)

Percentage of true positives Percentage of false positives

•Interpretable via Evett Table

•No information is provided about false negatives

•No information about the distribution of false scoresDo they affect a narrow range of scores? Do they widely perturb the system response?

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Supportability evaluation toolsSupportability evaluation tools 2/3 2/3

We propose to generalize the LRtest index using a new tool: the “Supportability of System” function (SoS):

•Interpretable via Evett Table

•Defined for both false positives and negatives

•Univocally detects the amount of false scores for each LogR

•Provides the accuracy of each score

SoS(x) = P(LogR>x | H0) / P(LogR>x | H1) if x>0

SoS(x) = [1- P(LogR>x | H1)] / [1-P(LogR>x | H0)] if x<0We know how much we can rely on our system, time by time!

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Supportability evaluation toolsSupportability evaluation tools 3/3 3/3

90% true

20% falseSoS=90/20=4.5

LogR = -13

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Score Score compensationcompensation tools 1/3 tools 1/3

original

translated

0 X

X

Preliminary operation:

Eliminate “false score only” areas encreasing or reducing all scores

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LogR=1

LogR=2

LogR=3

LogR=4

New LogR = LogR*tanh( Log10(SoS) )

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Compress all scores by a value defined by the SoS function

Reduced amount of false scores

compressed

original

Decreased values for true scores

Reduce the amount of false scores at the cost of a lower discriminative power

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Quality assessmentQuality assessment logics 1/3 logics 1/3

•Compensation increases for decreasing values of SoS

•Compensation is intrinsic to the system

•A good system must have a strong SoS for each LogR value

– Score compensation reduces system’s discriminative power

+ Score compensation is required to prevent unbalanced responses

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Quality assessmentQuality assessment logics 2/3 logics 2/3

DMTI procedure

•Step 1: test the system against a dataset (LogR)

•Step 2: calculate supportability (SoS)

•Step 3: calculate compensated scores (New LogR)

•Step 4: calculate the percentage P of new LogR which has a “strong” SoS score (fixed by our standards)

•Step 5: evaluate the Degree of Supportability (DoS):

DoS = atanh (2P-1)

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Quality assessmentQuality assessment logics 3/3logics 3/3

Regardless of the specific procedure, our DoS score is equivalent to a LogR score!

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Dipartimento di Meccanica e Dipartimento di Meccanica e Tecnologie IndustrialiTecnologie IndustrialiConclusionConclusion

• A general purpose tool has been developed to score system supportability

• An additional mathematic tool has been developed to compensate unbalanced systems

• The tools are system independent and theoretically motivated rather than empirically built

• The tools are useful to reduce both false positives and false negatives

• False score reduction produces a decrement in discriminative power

• Such decrement is intrinsic to the system response and is univocally usable for system quality assessment

• The proposed procedure for system quality assessment (degree of supportability) uses the well known Evett scale to score the system supportability

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Thank You for your attention…Thank You for your attention…

Questions?Questions?

Date post:	26-Mar-2015
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