Acoustic phonetics

Visualization of sound acoustic bacics

1. ACOUSTIC PHONETICS
NOTES BY JUNAID AMJED
LECT. ENGLISH DEPT.
IMIT COLLEGE
[email protected]
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2. INTRODUCTION
Acousticphoneticsisthestudyoftheacousticcharacteristicsofspeech,
includingananalysisanddescriptionofspeechintermsofitsphysical
properties,suchasfrequency,intensity,andduration.
Descriptionsofspeechsoundsinthesetermsdatebackasfaras1830
(Willis),buttheinventionofthesoundspectrograph(1945)wasthemajor
technologicalbreakthroughthatmadetheanalysisandvisualizationofthe
speechsignalpossible.
Acoustic Analysis
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3. INTRODUCTION
Subsequentdevelopmentsindigitalsignalprocessing,mostnotablythediscreteFourier
transform,havemadeitpossibletoconductallacousticanalyseswithabasicmicrocomputer.
Rousselot(b.1846–d.1924)iswidelyregardedasthe“fatherofexperimentalphonetics.”
Rousselotappliedthekymographtothestudyofspeech.Thekymograph,inventedinthe1840s
byLudwig,wasoriginallyusedformeasuringbloodpressureandotherphysiologicalprocesses.
Rousselot
Forspeech,thekymographconsistedofarotatingdrumcoveredwithpapercoatedwith
soot;speakersspokeintoarubbertubeandthesoundvibrationswerecapturedbya
stylusthatregisteredthevariationsinairpressure,fromwhichduration,intensity,and
pitchcouldbemeasured.
kymograph
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4. INTRODUCTION
Edison’sinventionofthephonographin1877wasofcrucialimportancesinceitwasthefirst
devicethatallowedtherecordingandreproductionofsound.Thisinventionmeantthat
speechwasnolongerafleetingeventbutcouldberepeatedlyheardandanalyzed.Anumber
ofresearchersdevelopedadditionaldevicestovisualizeandanalyzethesoundwaveforms,
includingHermann,Scripture,andVerner.Althoughthespeechwaveform(oscillogram)isthe
basisofallacousticspeechresearch,itisrarelyusedasasource.Oneimportantreasonisthat
itis“toorich”sinceitcontainsinformationaboutfrequency,intensity,andphaseofthesignal
components,whilehumanperceptiondisregardsthelatter.Hence,thespectrogramprovides
abetterrepresentation.
Edisonwith his phonograph in 1877
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5. PRACTICAL WORK
WAVEFORMS OF THE VOWEL /A:/ AND THE CONSONANT /S/
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6. PRACTICAL WORK
Acoustic Potencies Auditory Phonetics
Fundamentalfrequency (Hz)Pitch (how high or low do we
perceive a sound)
Intensity (dB) Loudness (how loudor soft the
reception of sound is)
Duration (t) Speech tempo (how fast or
slow we receive a sound signal)
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7. PRACTICAL WORK
Amplitude
The amplitude is simply a displacement of the vibrating medium from
its rest position.
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8. PRACTICAL WORK
Amplitude
Theamplitudeofawavereferstothemaximumamountof
displacementofaparticleonthemediumfromitsrestposition.Ina
sense,theamplitudeisthedistancefrom(positivesMaximum)
position.Similarly,theamplitudecanbemeasuredfrom(negatives
Maximum)position.
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9. PRACTICAL WORK
Fundamental Frequency
•Thetermfundamentalfrequencystandsforthecourseofthelowest
frequencyinaharmonicvibration,thereforeitisalsocalledF0.•„Frequencyis
atechnicaltermforanacousticpropertyofasound–namelythenumberof
completerepetitions(cycles)ofvariationsinairpressureoccurringina
second“(Ladefoged1975,162)
•the fundamental frequency is the lowest frequency of all other sinus
components in a spectrum •therefore it is called F0 •its whole-
numbered multiples (2x, 3x, 4x,...) are the so-called harmonic.
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10. WHERE ARE ALL THE OTHER FREQUENCIES PRODUCED?
•all frequencies that you find a speech signal come from the larynx
•whenwelookatthevocaltractasacylindricalpipewhichis
closedatoneend(glottis)andopenattheotherend(mouth)its
wavelengthisfourtimesitslength•afemalevocaltractisabout
15cmlong,whichmeansthatitswavelengthis60cm•atabout
35°Csoundtravelsatabout352m/sec
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11. SCHEMATIC VOCAL TRACT
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12. •acousticallythevocaltractisnotaverygoodpipe•energyisdampenedinevery
frequencyofthesourcesignal(comingfromthelarynx)•whatisnotdampenedso
mucharetheresonancefrequencies,whichshowasdarkshadingsinthe
spectrogram
•thelaryngealsignalhasmanyhigherharmonicswhichmeansthatenergycanalso
befoundinhigherfrequenciesthansimplythefundamentalfrequency•assaid
before,thevocaltractdampenscertainfrequenciesmoreandothersless
(dependingontheformationofthearticulators)•theseresonancefrequenciesare
calledformants
•formantsareapropertyofthevocaltractandcompletelyindependentfromany
sourcesignal(itdoesnotmatterwhetherthereisasourcesignalornot!!!)
•trythis:whisperthefollowing:heed,hid,head,had,hod,hawed,hood,who‘d
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13. Formants
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14. •The first two formants F1 and F2 are important for the intelligibility of
vowels
•Their position characterizes the spoken vowel.
•In order to understand each other, it is important that these formants are
similar in every speaker
Formants
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15. ”
“
I cannot teach anybody anything. I can only make them
think
― Socrates
NOTES BY JUNAID AMJED
Source: Acoustic theory of speech production.
Acoustic phonetics. Cambridge, MA: MIT Press.
Visible speech. New York: D. Van Nostrand.
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