Acoustic Theory

Human Vocal Apparatus Mid-sagittal planeX-ray of humanvocal apparatusMid-sagittal plane X-ray of human vocal apparatus78Schematic View of Vocal TractSpeech Production Mechanism •air enters the lungs via normal breathing and no speech is produced (generally) on in-take•as air is expelled from the lungs, via the trachea cords within the vibrate (Bernoulli oscillation) by the air flow•air is chopped up into quasi-periodic pulses which are modulated in frequency (spectrally shaped) in passing through the pharynx (the throat cavity), the mouth cavity, and possibly the nasal cavity; the positions of the various articulators (jaw, tongue, velum, lips, mouth) determine the sound that is produced Acoustic Tube Models DemoVocal Tract Tube Models11Tube Models 12Tube Models13Vocal Cord Views and OperationBernoulli OscillationTensed Vocal Cords –Ready to VibrateLax Vocal Cords –Open for BreathingGlottal volume velocity and resulting sound pressure at the mouth for the first 30 msec of a voiced sound•15 msec buildup to periodicity => pitch detection issues at beginning and end of voicing; also voiced-unvoiced uncertainty for 15 msec Glottal Flow 16Artificial LarynxArtificial Larynx DemoSchematic Production MechanismSchematic representation of physiological mechanisms ofspeech productionexciting •muscle piston bronchi •if vibrate,sounds •if through tract,producing point pressure pressure a brief /t/,18Abstractions of Physical ModelTime-VaryingFilterexcitation speechvoiced unvoiced mixedSpeech Waveforms and Spectra•••(aspiration,••over •the rapidly =>where 100 msec21Speech Sounds“Should we chase”/ould/ sounds /we/ sounds hard to distinguish weak sounds from silencehard to segment with high precision => don’t do it when it can be avoidedCOOL EDIT demo—’should’, ‘every’Estimate of Pitch Period -ITHIYHHV ZIYUWEstimate of Pitch Period -IIRAABFREHNZSource-System Model of Speech ProductionMaking Speech “Visible” in 194725Wideband and NarrowbandSpectrograms27Speech Sentence WaveformSpeech Wideband Spectrogram30Sound Source for UnvoicedSoundsParametrization of Spectra human vocal tract is essentially a tube of varying cross sectional area, orapproximated as a concatentation of tubes of varying cross sectional areasshows that the transfer functionoutput can be described in termsthe tubeknown as formants or formantfrequencies that pass the mostare 3 significant formants belowhighly efficient, compact representationSpectrogram and Formants36Waveform and SpectrogramEnglish Speech SoundsPhonetic Transcriptions•based on ideal (dictionary-based) pronunciations of all words in sentence–‘My name is Larry’-/M/ /AY/-/N/ /EY/ /M/-/IH/ /Z/-/L/ /AE/ /R/ /IY/–‘How old are you’-/H/ /AW/-/OW/ /L/ /D/-/AA/ /R/-/Y/ /UW/–‘Speech processing is fun’-/S/ /P/ /IY/ /CH/-/P/ /R/ /AH/ She had your dark suit in…SH AEIYHHRDAXR D KUWIH NS T YAA42“Wideband” SpectrogramSH AE IY HHRTD AXR D K UWIH NS YAAPhoneme Classification ChartVocal CordsVibratingNoise-LikeExcitationEY44Vowels and ConsonantsText 1: all vowels deletedTh_y n_t_d s_gn_f_c_nt _mpr_v_m_nts _n th_ c_mp_ny’s_m_g_, s_p_rv_s__n _nd m_n_g_m_nt.(They noted significant improvements in the company’s5051Vowel Articulatory Shapes•tongue hump position (front, mid, back)•tongue hump height (high, mid, low)•/IY/, /IH/, /AE/, /EH/ => front => high resonances •/AA/, /AH/, /AO/ => mid => energy balance•/UH/, /UW/, /OW/ => back => low frequency resonances52Vowel Waveforms & SpectrogramsSynthetic versions of the10 vowelsVowel Formants54The Vowel TriangleCentroids of common vowels form clear triangular pattern in F1-F2 spaceiy-ih-eh-ae-uh55Canonic Vowel SpectraIYAAUW IYAAUW100 Hz Fundamental10 Hz33 Hz100 Hz56Canonic Vowel SpectraIYAAUWUW100 Hz FundamentalIYAA300 Hz Fundamental300 HzEliminating Vowels and Consonants58Diphthongs•Gliding speech sound Distinctive FeaturesClassify non-vowel/non-diphthong sounds in terms of distinctive featuresplace of articulation•Bilabial (lips)—p,b,m,w•Labiodental (between lips and front of teeth)-f,v •Dental (teeth)-th,dhPlaces of Articulationuh-{w,l,r,yeven higher frequency zerouh-{m,n,ng}-aNasal SoundsUH M AA UH N AAHole inspectrum65Nasal Spectrograms Unvoiced Fricatives•Consonant sounds /F/, /TH/, /S/, /SH/–produced by exciting vocal tract by steady air flowwhich becomes turbulent in region of a constriction inthe vocal tract•/F/ constriction near the lips•/TH/ constriction near the teeth•/S/ constriction near the middle of the vocal tractresonances (zeros of transmission)uh-{f,th,s,sh}-a6768Unvoiced FricativesUH F AAUH S AA UH SH AA69voiced-like componentuh-{v,dh,z,zh}-aUH V AA UH ZH AAVoiced Fricativessuddenly releasing the pressure, resulting in a pop-like soundno sound is radiated from the lips during constriction =>sometimes sound is radiated from the throat during constriction uh-{b,d,g}-aVoiced Stop ConsonantUH B AAUnvoiced Stop ConsonantsUH P AA UH T AAStop Gapuh-{p,t,k}-auh-{j,ch,h}-a76Stop Consonant Waveforms and Spectrogramsuh-{p,t,k}-auh-{j,ch,h}-a77•the brain recognizes sounds by doing a distinctive feature analysis from the information going to the brain•the distinctive features are somewhat insensitive to noise, background, reverberation => they are robust and reliable78Distinctive Featuresplace and manner of articulation completely define the consonantsounds, making speech perception robust to a range of external factorsEnjoy:Simple:82This is a test (16 kHz sampling rate)TH-IH S IH Z UH T EH S T83Word Choices:Top Row: simple; enjoy; those Second Row: was; between; companyAB C D E Spectrograms of CitiesCity Choices: Chicago, Denver, Los Angeles, Memphis, SeattleLos AngelesChicagoDenverSeattle Memphis85Word Choices:that, and, was, by, people, little, simple, between, very, enjoy, only, other, company, those/was/ --this word can be identified by the voiced initial portion with very low first and secondformants (sounds like UW or W), followed by the AA sound and ending with the Z (S) sound.Word Choices:that, and, was, by, people, little, simple, between, very, enjoy, only, other, company, those/enjoy/ –this word can be identified by the two-syllable nature , with the nasal sound N at the end of the firstsyllable, and the fricative JH at the beginning of the second syllable, with the characteristic OY diphthong at the end of the word87Ultimate Exercise—Identify Words From Spectrogram Word Choices:that, and, was, by, people, little, simple, between, very, enjoy, only, other, company, those/company/ –this word can be identified by the three syllable nature , with the initial stop consonant K, the first syllableending in the nasal M, followed by the stop P , and with the second syllable ending with the nasal N followed by an IY vowel-like sound88Ultimate Exercise—Identify Words From SpectrogramWord Choices:that, and, was, by, people, little, simple, between, very, enjoy, only, other, company, those/simple/ –this word can be identified by the two-syllable nature , with a strong initial fricative S beginning the first syllable and the nasal M ending the first syllable, and with the stop consonant P beginning the second syllable。