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BBN–ANG–141 Foundations of phonology

Phonetics 3: Acoustic phonetics 1

Zoltán Kiss

Dept. of English Linguistics, ELTE

z. kiss (elte/delg) intro phono 3/acoustics 1 / 49

Introduction


Introduction

contrast

beer ←→ bear


Introduction

contrast: how?

?what makes the contrast possible?


Introduction

some basic terms


Introduction

acoustic cues


sound waves

acoustics

definition and etymology

◮ acoustics is a branch of physics and is the study of sound (which ischaracterized as mechanical waves in gases, liquids, and solids)

◮ acoustic is derived from the Greek word Ćkoustoc ‘able to be heard’

◮ it is concerned with the production, control, transmission, reception,and e=ects of sound

◮ it aims at describing and quantifying the properties of sounds with thehelp of various wave-related models

acoustic phonetics

deals with the acoustic properties and quantification of speech sounds


sound waves

what is sound?

whenever there is a sound, there is:

sound transmission

◮ sound source

◮ transmission through a medium (e.g., air, water)

◮ potential receiver/interpreter

the definition of sound

Sound is a potentially audible disturbance of a medium produced by avibrating source.


sound waves

how to measure sounds?

two problems:

◮ sound is invisible

◮ most sounds are fairly complex

the task:

◮ make sound visible for analysis

◮ deal with the simplest sounds first


sound waves

the simplest sounds: pure tones

the tuning fork emits pure tone


sound waves

the sound of the tuning fork


sound waves

simple periodic motion (SPM)

the SPM of the tuning fork

◮ the tines of the tuning fork vibrate in simple

periodic motion

◮ the tines move back and forth one fixed

number of times per second

(no matter how hard the fork is struck)

◮ periodic motion: the pattern repeats itselfuntil it damps out


sound waves

simple periodic motion (SPM)

the SPM of the tuning fork

◮ a complete movement:starting/rest position >maximum displacement >back over starting position >maximum displacement >back to starting position= a cycle (c)

◮ frequency (F): the number of completedcycles per second (s) (Hertz (Hz) or cps)

◮ the tines complete 440 cycles per second,frequency of the tuning fork = 440 Hz


sound waves

more simple periodic motion (SPM):

the swing & the pendulum of the grandfather clock


sound waves

graphing SPM

Let’s try to record SPMin a graph!

(demo)


sound waves

graphing SPM: sound wave/waveform


sound waves

graphing SPM: sinus waveform


sound waves

2 definitions

waveform

A graphical display of how amplitude varies over time.

simple harmonic motion (SHM)

A motion whose waveform is a sinus wave.

−→ the SPM of the tuning fork is a simple harmonic motion


sound waves

waveform properties

2 independent properties:

1. TIME, expressed as period (T) = time for a cycle to complete(expressed in seconds)◮ in the graph T = 0.01 sORfrequency (Hz) = number of cycles in a second◮ in the graph frequency = ??? Hz

2. (PEAK) AMPLITUDE: the distance from the zero crossing


sound waves



sound waves

the propagation of sound: pressure wave movement


sound waves

sound propagation (of the pure tone): summary

◮ SHM of sound source

◮ SHM of air particle set in motion by source

◮ air particle moves in sympathy with the SHM of source

◮ individual particle has limited motion

◮ areas of air compression and rarefaction /�re@rI"fækSn/ are created

◮ compression and rarefaction areas move in time away from source,transmitting the SHM of source (pressure wave movement)

◮ listener senses same SHM as that of the source: sound has beenpropagated


sound waves

representations of sound propagation: waveform


sound waves

graphing SHM of air particles: waveform


sound waves

pressure-based graph

– variations in air pressure with respect to an equilibrium /�i:kwI"lIbrI@m/


sound waves

pressure-based grap: sinuosoid waveform

– variations in air pressure with respect to an equilibrium /�i:kwI"lIbrI@m/


sound waves



frequency

change in frequency⇒ subjective sensation of pitch


frequency

some important facts about frequency

◮ when a sound is twice the frequency of another sound, it is an octave

higher

◮ frequency range of human hearing: 20 Hz–20,000 Hz

◮ speech sound analysis usually involves the range between100 Hz–10,000 Hz


frequency

change in amplitude⇒ subjective sensation

of loudness/intensity


amplitude

the decibel: a measure of relative intensity

why the decibel scale?

◮ air pressure amplitude is measured in pascals (Pa)

◮ the pascal scale is a linear scale: each increment is equal to the next

◮ the sensation of sound loudness/intensity is related to amplitude;however,

◮ it is not linear but logarithmic, that is,

◮ it is constructed with increments with increasingly larger numericaldi=erences

◮ the decibel (dB) scale (or “sound pressure level (SPL) scale”) is alogarithmic scale of the amplitude of air pressure variations

◮ the dB scale has intervals that are roughly equal to perceived loudness


amplitude

0 dB = 20 µPa(the threshold of hearing; the buzz of a mosquito around 3 meters away)


amplitude

80 dB (≈ 100000 µPa)(average street tra;c)


amplitude

140 dB (= 100,000,000 µPa)(threshold of pain; jet engine at 25m distance)


synthesis

?what about complex sounds?!

(speech sounds are nothing like pure tones!)


synthesis

how can we characterize complex waves?

Jean Baptiste Joseph Fourier(1768–1830)

◮ key idea: if we can reduce a complex periodic waveform into acombination of sine waves

◮ then we can describe it using information about the frequency andamplitude of each component sine wave


synthesis

to build a complex wave is like a recipe, e.g., take

◮ 1 100 Hz/30 dB sinus wave, then add

◮ 1 200 Hz/10 dB sinus wave, and also add

◮ 1 300 Hz/20 dB sinus wave

This addition of two or more di=erent sine waves to create a complexperiodic wave is called synthesis.


synthesis

waveform of a complex tone derives from 2 or more pure

tones of di=erent frequency and/or amplitude


synthesis

three important consequences of synthesis

◮ the amplitudes of the complex wave depends on the addition of theamplitudes of the component waves

◮ the sine wave with the smallest frequency will define the main/basicrepetition frequency of the complex wave: fundamental frequency f0

◮ the other sine wave frequencies present in the complex wave are calledharmonics (H) (or: overtones);

harmonics and f0

harmonics are integer (whole number) multiples of the f0(this is because each sine wave component must complete a whole number of cycles within

one period of the complex)


harmonic analysis

Our example complex wave has this harmonic series

(also called Fourier series):

Harmonic Frequency Amplitude

H1 (= f0) 100 (100× 1) Hz 30 dBH2 200 (100× 2) Hz 10 dBH3 300 (100× 3) Hz 20 dB

harmonic analysis

the reverse of synthesis, finding (characterizing) the component sine waveharmonics of the complex wave


harmonic analysis

Fourier’s theorem (1822)

◮ All complex periodic waveforms can be analysed into a sum ofsinusoidal component waveforms (harmonics).

◮ The mathematical algorithm of this process of harmonic analysis iscalled Fourier analysis or Fourier transformation.


harmonic analysis

?how can we graphically represent harmonic analysis?


harmonic analysis

spectrum graphs

◮ the (power/amplitude/line/sound) spectrum (plural: spectra): is a plotof the results of harmonic analysis

◮ frequency of harmonic: horizontal axis

◮ amplitude of harmonic: vertical axis

◮ time and phase: not shown (Fourier analysis is taken at a particularinstant of time)


harmonic analysis

harmonic series of D

harmonic freq. ampl.first (=f0) 100 Hz (100 × 1) 30 dBsecond 200 Hz (100 × 2) 10 dBthird 300 Hz (100 × 3) 20 dB


harmonic analysis

loudness, pitch, quality: a summary

◮ all these components are independent of each other:

◮ sound loudness depends on amplitude

◮ sound pitch depends on f0◮ sound quality/timbre depends on the spectrum (harmonic series)


harmonic analysis

contrast: depends on the spectrum

beer ←→ bear


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