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Formant-Pattern Estimation Guided by Cepstral Compatibility. Frantz Clermont Philip Harrison Peter French J.P. French Associates & University of York United Kingdom. IAFPA Conference Plymouth, UK 23-25 July 2007. Central to Acoustic Phonetics Crucial to Forensic Phonetics

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formant pattern estimation guided by cepstral compatibility

Formant-Pattern Estimation Guided by Cepstral Compatibility

Frantz Clermont

Philip Harrison

Peter French

J.P. French Associates & University of York

United Kingdom

IAFPA Conference

Plymouth, UK

23-25 July 2007

a long standing problem how reliable is the measured formant pattern

Central to Acoustic Phonetics

  • Crucial to Forensic Phonetics
  • Central to a Major Debate in

Speech & Speaker Recognition

  • SHORT ANSWER:
  • STILL NO OBJECTIVE WAY OF ENSURING/CHECKING RELIABILITY

OF MEASURED F-PATTERNS

  • APPRECIABLE VARIABILITY AMONGST SOFTWARE PACKAGES

(HARRISON, 2004)

  • WAYS FORWARD – WHAT ARE WE TO DO?
  • THROW OUR HANDS IN DESPAIR & SIMPLY USE AVAILABLE TOOLS?
  • STILL HOPE FOR SOME VIABLE SOLUTIONS?

A Long-Standing Problem: How “reliable” is the measured formant-pattern?

a new approach particulars aims
A New Approach: Particulars & Aims
  • Objectivity & Reliability of F-pattern Estimation
      • Compatibility with the observed spectrum
      • A “Smart” Measure of Compatibility
  • We use a related representation: The Cepstrum
      • Efficient approximation to the exact spectrum
      • More readily available from speech signal
      • Contains vocal-tract resonance information
      • Robustness in speech and speaker recognition
  • We propose a Cepstral Analysis-by-Synthesis Method
      • To generate Candidate Cepstra
      • To determine most compatible candidate w.r.t observed cepstrum
pathway to speech spectrum

Linear Prediction (LP)

ALL-POLE FILTER

FILTER ORDER

M

Pathway to Speech Spectrum

Source-Filter

MODEL

N.B. “OPTIMUM” M UNRESOLVED ISSUE!

pathways to formant patterns cont d lp derived cepstrum order m

A Vocal-Tract Parameter

A Fourier-Series Model

of EXACT LP-Spectrum

Pathways to Formant Patterns (cont’d):LP-derived Cepstrum (order M)

M÷2 POLES

{BROAD & NARROW BANDWIDTHS}

cepstral analysis by synthesis cabs

ACOUSTICSIGNAL 

FRAMES 

OBSERVEDCEPSTRUM

CEPSTRAL

DISTANCE

LP CEPSTRUM

order M = 12

CANDIDATE

CEPSTRA

LP CEPSTRUM

TO POLES

M÷2 = 6

GENERATE

ALL UNIQUE

QUARTETS 

BINOMIAL (6,4)

CEPSTRUMCONVERSION

Cepstral Analysis-by-Synthesis (CAbS)

some vowel data to test the approach

MICROPHONE

TELEPHONE

Some Vowel Data to Test the Approach

Harrison (2004)

THIS

STUDY

(1 speaker)

  • 2 adult-male, native speakers
  • 3 contemporaneous tokens
implementation methodology

4.5

Candidate Values of Upper Bound (kHz)

10

11

18

2.6

2.5

Candidate Values of M

POLE-GRAM (LP-ORDER M = 10)

+

CAbS RESULTS SUPERIMPOSED

(Upper Bound = 3.5 KHz)

Implementation Methodology

CALCULATEAVERAGE

INTRA-VOWEL

DISPERSION

CLUSTERING

QUALITY

(CQ)

results 1 optimisation of analysis parameters lp order spectral range

Opt. M = 13

[3300 – 4200] Hz

CQ = 27.05 Hz

MICROPHONE

TELEPHONE

Opt. M = 10

[3300 – 3700] Hz

CQ = 27.80 Hz

Results 1: Optimisation of Analysis Parameters (LP order & Spectral Range)

concluding summary
Concluding Summary
  • Introduced a New Approach to F-pattern Estimation
      • Two major schools of parameterisation – the formant & the cepstrum
      • F-patterns estimated by requiring compatibility w/ observed cepstra
      • Compatibility is achieved using a “smart” measure of compatibility
          • sensitivity to spectral peaks that provide the best spectral match
          • flexibility to select any spectral range
  • Current Results are Promising
      • Compatibility Measure exhibits Robustness
      • Estimated F-patterns are Consistent with Phonetic Expectationz
      • LP-Order and Spectral Range are Concurrently Optimised
  • Proposed Approach – A Serious First Step towards
      • Objectivity
      • Reliability
      • A Very Useful Tool
looking towards the future
Looking towards the Future
  • More Challenging Data
      • Beyond Steady-State Vowels
      • Wide Range of Speakers
      • Variety of Voice Qualities
      • Differing Recording Conditions
  • Speculations
      • The All-Pole LP-Model is likely to be insufficient

for all cases

      • The Approach of Cepstral Compatibility holds

the potential of a long survival!