Physics of speech

Question 1

Acoustic phonetics

Answer 1

study of sound waves made by the human
vocal organs for communication.

study of the physical properties of speech,
and aims to analyse sound wave signals that occur within speech
through varying frequencies, amplitudes and durations

Question 2

Speech Waveform

Answer 2

transmitted through air (and other medium) as a regular
wave of pressure changes

changes in air pressure

• can be heard
• cannot see
• can be measured
• measurement can be visualized and used for statistical calculation

Question 3

basic parameters of the speech signals

Answer 3

• amplitude

* time (duration)

Question 4

main derived parameters of speech signals

Answer 4

• Intensity
• noise vs. resonance
• frequency and formants

Question 5

methods used to analyse speech signals

Answer 5

• analog-to-digital (A/D) conversion

* mathematical definitions of filters and transformations

Question 6

Visualisation for Speech Signals

Answer 6

need to know

• time
• amplitude
• oscillogram
• spectogram
• formants
• fundamental frequency
• pitch track

Question 7

Time Domain

•

Answer 7

What actually appear in your waveform if you zoom it in

The positive or negative amplitude A of the speech signal at any given
point in time is the distance of the wave from zero at this point in
time

Question 8

What can be derived from time domain analysis? Intensity

Answer 8

intensity of the speech signal at any given point
in time is the square of the amplitude of the wave
from zero at this point in time: I = square(A)

Question 9

What can be derived from time domain analysis? Period or interval

Answer 9

duration of this single wave

• signal is resonant if its period are regular in duration
• signal is noisy if period is irregular in duration

Question 10

wavelength λ (lambda)

Answer 10

speed of sound in m/sec divided by the number of periods per second

distance between successive peaks is called wavelength. measured in meters / cm

Question 11

wave

speed

Answer 11

v = λ / T
v = λ f

Question 12

Frequency Domain: Simple & Complex

Signals

Answer 12

frequency of a speech signal is the number of waves (periods) per second in the waveform

Question 13

The source larynx

Answer 13

only valid for voiced sound

• Fundamental frequency
about 80 Hz - 150 Hz for men (greater range possible)
about 160 Hz – 300 Hz for women (greater range possible)

• Several overtones/harmonics of the fundamental frequency
• different intensities of overtones, relative to each other, which determines
  the overall waveform

during voicing, the larynx generates a waveform which is rather like a “sawtooth” sequence

Question 14

Frequency Domain: Complex Signals

Answer 14

• Combination of several arbitrary sine waves resulting noise
• But if it is not arbitrary, it produce harmonic wave

• The lower frequency is the F0
• The higher frequencies in a harmonic waveform are harmonics or
overtones of the F0

Question 15

The filter system

Answer 15

consists of pharyngeal, nasal, oral cavities, with
resonant frequencies which amplify or damp the overtones with these frequencies

These filter frequency bands are called formants

Formant frequencies of the oral cavity can be modified by the variable filters (articulators such as tongue and lips)

Question 16

Acoustic Resonance

Answer 16

understand how resonator (vocal tract) modified the complex periodic sound

Question 17

How we get a speech sound

Answer 17

sound source

sets vocal tract into resonance depends on its shape

amplifies some freq and attenuates others

speech sounds come out

Question 18

Source-Filter Theory

Answer 18

speech is a product of interaction between a sound source (vocal folds/phonation) and a filter (vocal tracts/resonance)

sound source (vocal folds/phonation) sometimes referred as source function

filter (vocal tract/resonance) sometimes referred as filter function / transfer function

Question 19

Filter function

Answer 19

supralaryngeal vocal tract can be characterized by a filter function (length and shape of tube)
which specifies (for each input frequency from the source) the relative
amount of energy that is passed through the filter and out of the mouth

peaks in the vocal tract filter function are the resonances of the vocal tract
reflect the frequencies which are passed through the filter with the greatest
relative amplitude

Question 20

Source and Filter: Independence

Answer 20

Formants = resonant frequencies of the vocal tract
- depends on shape of vocal tract to filter harmonics
- do not depend on f0 of the sound source
source and filter are independent of one another

Question 21

Varying the Filter: Vocal Tract Shape

Answer 21

vocal tract = variable resonator

shape constantly changes over course of utterance
- space in oral cavity can be large/small
- space inpharyngeal can be L/s
air can resonate in nasal cavity / blocked from nasal cavity

changeing shape of vocal tract =

• change resonating frequencies
• change filter
• different speech sounds

each sounds has its own filter made up of its own set of resonant frequencies (formants)

Question 22

Source Filter Model

Answer 22

spikes (harmonics) are generated by SOURCE
peaks (formants) are generated by FILTER

single spectral analysis of an interval in a speech signal requires at least 1s

sequence of spectra is neede to track the changing structure of speech signal

the representation of sequence of spectra is called spectogram

Question 23

Source Filter Model

Answer 23

spikes (harmonics) are generated by SOURCE
peaks (formants) are generated by FILTER

single spectral analysis of an interval in a speech signal requires at least 1s

sequence of spectra is neede to track the changing structure of speech signal

the representation of sequence of spectra is called spectogram