# Acoustics final ch 2 and 3

 The flashcards below were created by user elz125 on FreezingBlue Flashcards. What are the levels of speech? Linguistic for speakerPhysiological for speakerAcoustic- sound wavesPhysiological for listenerLinguistic for listener Which level is the easiest to study? acoustic level Linear source-filter theory expresses articulatory-acoustic relationships*one of the most important/best theories in our field What is involved in speech production? need a power source (breath support)we get a complex periodic signal from the vocal folds (the vibrate in 3 different ways and come togetherspeech is changed by changing the shapes of your cavities What is the source of sound for speech? vocal folds (vibration)*for some consonants, the source is more complex (can be in the vocal tract or a combination of both- voiceless sounds) What makes you sound like you? shapes of pharynx, nasal, and oral/mouth cavities What is the filter for speech? vocal tract (frequency dependent like all filters)resonator (air filled cavity) What does the resonator do for you? natural frequencies change in resonator (ear does everything for you so you can perceive differences)3-6 syllables per second How are the source and filter related? they are assumed to be independent of each other (an assumption made for convenience)this implies that you can change the output of the vocal folds without changing the vocal tract and vice-versa What do the vocal folds and vocal tract give you? vocal folds- fundamental frequency, harmonics, and amplitude changesvocal tract- articulation How are vowels modeled? as a tube closed at one end and open at the other What is the formula to calculate where the resonant frequencies will be? Fn = (2n-1)c/41Fn = resonant frequencyn = integer (if looking for 1 you put 1, if looking for 2 you put 2, etc)c = speed of sound/4 times the length of tube What is the first resonant frequency with a tube length of 17 cm and speed of sound is 34,000 cm/s? Fn = (2n-1)c/41(2-1)*34000/(4*17) = 500 Hz*the longer the tube the lower the resonant frequencies, the shorter the tube the higher the resonant frequencies How many resonances are there for a tube? infinitewe only need to consider the first 3 or 4 (the model is valid to only about 5 kHz) What happens when the shape of the tube changes going from one vowel to another? resonant frequencies change Why doesn't changing the frequency/energy of the source of vibration change the resonant frequencies of the pipe/vocal tract? the source and filter are independent of one another What are formant frequencies? resonant frequencies of vowels*do NOT confuse with fundamental frequency! How do a curved tube (vocal tract) and a straight tube (model) behave out to 5 kHz? indentically acousticallythe curve begins to affect acoustic signals with a short wavelength What happens if the tube has uniform cross sectional area? the resonances are equally spaced Does all of the energy come from the source or filter? sourcevocal fold vibration for vowels What does changing the length of the tube do? changes the resonance frequenciesinfluenced by age and sexl = 14.5 cm for femalesl = 8.75 cm for children What does every formant/resonant/natural frequency have? its own frequency, amplitude, and bandwidth How are different vowels modeled? acoustically by different vocal tract shapes Phonetically, how are vowels distinguished? position of the tongue What happens if a constriction is placed on the tube/vocal tract? the resonances change What happens if you change the articulation? you change the vocal tract shape, and the resonance frequencies, amplitudes, and bandwidths *Ch. 2 slide 14 The output energy of a vowel is the product of: the source energythe size and shape of the resonatorthe radiation characteristics (adds 6 dB)increases in frequency by 6 dB + 6 dB (constant)- output is actually -6 dB What are glottal source characteristics for vowels? vocal fold vibration is periodicfo or F0 is used to indicate the vocal fundamental frequencythe amplitude of the harmonics decreases by -12 dB/octave What gives you amplitude changes? sourceonly changing source and not filter makes resonant frequencies stay the same *Ch. 2 slide 19 What are filter characteristics for vowels? the vocal tract is a dynamic filter (changes constantly)it is frequency dependentit has, theoretically, an infinite number of resonances (only care about 1st 3 or 4 for vowels)each resonance has a center frequency, and amplitude and a bandwidthfor speech, these resonances are called formantsformants are numbered in succession from the lowest (F1, F2, F3, etc)the formants together form the transfer function (input-output relationship; formants become physically evident only when energized) Which harmonic has the highest amplitude? the one closest to the vowel What is radiation characteristic? acoustic effect when a sound leaves a small area and enters a large one (like speaker)the effect is to raise the slope of the spectrum by +6 dB/octave *What are the acoustic phonetic relationships for vowels? F1 is inversely related to tongue height (raise tongue, low F1 and vice versa)F2 is directly related to tongue advancement (back vowels have low F2, front vowels have high F2)lip rounding lowers all formant frequencies (because you're making the vocal tract longer)you can calculate how close a person is to the sound they are trying to make What does perturbation mean? constriction What is the perturbation theory? volume velocity variations reflect the way air particles vibrate at a particular point in the vocal tract (how the air is passing through vocal folds)at some points, vibration is minimal (node); at others, maximal (antinodes)for F1, the antinode is at the open end of the tube (mouth) and the node is at the closed end (vocal folds)for F2, there are 2 antinodes and 2 nodes, etc Where is there always an antinode? lips Where is there always a node? vocal folds What happens when there is a constriction near a node? formant frequency will increase What happens when there is a constriction near an antinode? formant frequency will decrease Perturbation theory, if a change in cross sectional area is applied (a perturbation): the acoustic effect depends on proximity to a node or an antinode (antinode = lower freq.; node = higher freq.)lip constrictions lower all formant frequencieslaryngeal constrictions raise all formant frequencies What do amplitudes depend on? formant frequencies If F1 is lowered (raised), what happens to A1? it lowers (rises) If 2 formant frequencies move closer together: both peaks increase in amplitude How do you raise or lower formant frequencies? change articulators (3-6 syllables per second) What are source-filter interactions? independent of one anotherBUT some vocal tract shapes may affect vocal fold vibration:singers' formant (to be heard over background noise)high impendance constrictions require greater subglottal air pressurevocal tract - vocal fold coupling during open phase of vibratory cycle What can the linear source-filter theory be used to describe? the acoustics of consonants as well as vowels Why, for consonants, is the source not always at the level of the vocal folds? some sources are in the vocal tractthese sources are aperiodicdurations and amplitudes also are different from vowels What does the source-filter theory give us? a series of expectations for the acoustic characteristics for consonants How are fricatives modeled? as a tube with a very severe constriction What are characteristics of fricatives? the air exiting the constriction is turbulentzeros or antiformants can be found in the spectrumbecause of the turbulence, there is no periodicity unless accompanied by voicing What are characteristics of nasal consonants? velopharyngeal port is open and the oral cavity is completely blocked at some pointthe side-branch resonator produces antiformants (zeros)the overall vocal tract is longer than for vowelsoral formants, nasal formants, nasal antiformantsnasal murmur What are characteristics of stops? the tube model is not altered very muchtime domain is criticalthere is a complete closure of the vocal tract somewherepressure builds up behind the closurerapid releasearticulation results in a burst and transitions What does analog mean? storing ALL the information on a wave What does digital mean? samples at specific times along wave at each frequency and takes few points and stores the information (connects the dots for you and doesn't record amplitudes) What is a spectrograph? an instrument the can capture the dynamics of speechacoustic signals vary only in frequency, amplitude and time; the sound spectrograph captures all of these What is a spectrogram? the output (usually a hardcopy) of a spectrograph What is a wide-band filter good for? looking at formant frequencies What is a narrow-band filter good for? looking at harmonics and fundamental frequency What is abscissa? timex axis What is ordinate? frequencyy axis What do black areas of a spectrogram indicate? highest amplitudes What do white areas on a spectrogram indicate? the noise floor What do shades of gray in a spectrogram indicate? intensityamplitudes between highest amplitude and noise floorthe more intense the signal is at a particular frequency and time, the darker the trace What is the Nyquist theorum? in order to represent a signal faithfully, it must be sampled at a rate equal to twice its highest frequencyif you don't pick the right sampling rate, you don't get accurate output (if you get the wrong output, all your measurements are wrong) What is presampling or brickwall filtering? removes all of the energy above the nyquist frequencythe clinician/researcher determines the Nyquist frequencysome knowledge of speech and speech and language disorders is required What is aliasing? when the output doesn't match the inputwhen you don't follow Nyquist rule What are discrete numbers? dots along wave (not continuous measurement) What is sampling rate? how many times you take a discrete number What is sampling? how many times per second the amplitude will be recorded What does sampling for digital signal processing do? analog-to-digital conversionsignal must be sampled at the Nyquist ratesampling rate decides the times at which the signal will be sampledsampling converts the acoustic signal into a series of numbersinstead of amplitudes at all instances of time, no matter how small the time interval, amplitudes in the digital world exist only at the sampling interval What happens to the samples determined by the sample rate? they are chopped into discrete numbers (converting amplitude variations into discrete numbers) What is quantization? discrete number of amplitude levelsthe more quantizer levels available, the more the discrete signal represents the original analog signal (higher the rate, smaller the interval)in our applications, 16 -bit quantizers over a 20-volt range are typical (this yields an amplitude resolution of 300 microvolts and a signal to noise ratio of 96 dB) What happens after A/D (analog to digital) conversion? the signal is stored as a stream of numberstime is related by the index to the sampling ratethe amplitude is the stored number (quantization process)in this form, many operations can be performed (you can do anything you want) What is involved in a waveform display? duration measurements (speech changes gradually)signal editingamplitude measurements (rms is most common)vocal fundamental frequency *some consistent rules need to be adopted for duration and signal editing What is a digital spectrograph? a series of spectra based on the FFT (fast Fourier analysis) or LPC (linear predictive coding) How is amplitude depicted in a digital spectrograph? as shades of gray What is an example of a digital spectrograph? praatdoes the work for us What is linear predictive coding (LPC)? you can predict where the next dot (amplitude) will be based on previous cycles (as few as 10 to 15 previous samples is all that is required)speech does not generally vary wildly from sample to sample (highly predictable) What is the equation for LPC? y = a0 + a1(x-1) + a2 (x-2)+....y = amplitude of the next samplex = one of the previous samplesa = estimates of the resonances of vocal tract (can represent sections of vocal tract)allows you to talk on the phone (can guess what speech will be so it only has to transfer so many numbers)individuals with voice/hearing problems have problems with being understood on the phone What is a wideband spectrogram? short time window (.005, .007, .009)good for measuring formant frequencies (of vowels) What is a narrowband spectrogram? long time window (.1, .05)good for showing and measuring harmonics Authorelz125 ID119668 Card SetAcoustics final ch 2 and 3 DescriptionAcoustics of speech and hearing Updated2011-12-11T02:11:52Z Show Answers