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Speec ana ys s

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Analysisofspeechsoundstakingintoconsiderationtheirmethodof

production

acoustic featurevectors.

``

eex rac on o n eres ng n orma onasanacous cvec or

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ResonancesandFormants Resonances are vibratory characteristics of a resonating body.

In the case of an air filled tube the resonance characteristics exist

even when there is no sound being produced.

selectively enhance sound vibrations close to the resonance

frequencies and selectively attenuate sound vibrations remote from.

This results in peaks in the acoustic spectrum of the resulting

speech sound.

These acoustic s ectral eaks are called formants articularl

when they occur in vowels and vowellike consonants.

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Spectrograms

pec rogramsperm eexam na ono e ynam cc anges naspeechspectrum. consonants(eg.stopbursts)andalsoforvoweltransitions(betweenvowelsandconsonantsandbetweenthetargetsindiphthongs). Spectrograms,usuallyinconjunctionwithwaveforms,areessentialduringthesegmentingandlabelingofspeech. Spectrogramsusuallyprovidetheclearestvisualcuestotheboundariesbetweenphonemes.

Spectrogramsdonot,however,provideaccuratemeasurementsofvowelformantsasbroadband spectrogramshaveapoorfrequencyresolution(about300Hz)andsothereisahighdegreeofintrinsic

.ThatiswhywetendtouseFFTsandLPCsfortheaccuratemeasurementofformantfrequencies.

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Fig: waveformandbroadbandspectrogramoftheword"heard"

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0.0143017892 0.490396511

1_aam

g1 g2 aag aa1 aa2 aam m1 m2

Time s

0 0.491

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aayvu

1

-1

0

g aa ay y yv v vu u

Time (s)

0 0.8455

0.2 0.1 0.07 0.04 0.07 0.07 0.19.

Words Duration

insecsIntensity

indBPitch

inHzFormantsinHz

F1 F2 F3 F4

aayvu 0.77 80.4 160.2 540.7 1484.6 3750.3 3750.2

. . . . . .

aa 0.2 81.3 137.1 810.4 1181.6 2865.5 3792.2

ay 0.1 84.0 171.1 654.07 1755.3 2599.9 3753.5

y 0.07 80.5 179 362.1 2275.9 2570.3 3878.4

yv 0.04 78.7 174.5 349.3 1928.6 2365.0 3876.5

. . . . . . .

vu 0.06 78.2 166.5 3636.0 1147.2 2570.8 3568.2

u 0.2 77.8 167.2 387.36 1488.5 2611.5 3693.2

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Hz)

LPC of aa in aayvuLPC of aa in aayvu

886.4 1212.5

relevel(dB

40

2916.7

3754.0 4813.6

Soundpress

20

Frequency (Hz)0 55000 1000 2000 3000 4000 5000

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B/

Hz)

60

LPC of v in aayvu

323.3

pressurelevel(d

40

1190.2

2346.2 3613.2

Frequency (Hz)

0 5500

Sound

20

0 1000 2000 3000 4000 5000

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B/

Hz)

LPC of u in aayvu

397.4

1486.33583.6

pres

surelevel(d

40

60 2590.7

Frequency (Hz)

0 5500

Sound

20

0 1000 2000 3000 4000 5000

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Linear Prediction Coefficient (LPC)

the poles (related to resonances or formants) that, when combinedwith the speech source spectrum (the "residual" in LPC analysis),would result in the ori inal waveform.

An LPC analysis separates the analysis of the resonantcharacteristics of a speech sound from the source characteristicsof that sound.

The resulting LPC spectrum is a smoothed spectrum with thepeaks representing the formants (resulting from the vocal tract

- .

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Figure:Whitenoiseusedasasimplifiedmodelofafricativesoundsource.

Notetherandompatternofboththewaveform(bottom)andthe

spectrum(top).Alsonotethatthespectralenvelope(LPCspectruminred)

isapproximatelyflat.

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Identification of Speech Waveforms

Figure: Threelongvowelsinan/h_d/context.

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Figure: ThreeEnglishvoicelessoralstopsinCVcontext

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