Elements of Acoustic Phonetics

224 Pages·5.295 MB·English

by  Ladefoged, Peter

ELEMENTS
OF ACOUSTIC
PHONETICS

2 ND
EDITION ..____,
ELEMENTS or
A(0USTI(
PHONETICS
Peter Ladefoged
I H E U N I V E R S I T Y 0 F ( H I C I 6 0 F I E SS
( H I C I G 0 A N D l 0 N D ON
'1'he University of Chicago Press, Chicago 60637
The University of Chicago Press, Ltd., London
© 1962, 1996 by Peter Ladefoged
All rights reserved. Published 1996
Printed in the United States of America
1009fl8D70605040302 345678
ISBN: @226-46763-s (cloth)
0-225-46764-s (paper)
Library of Congress Cataloging-in-Publication Data
Ladefoged, Peter.
Elements of acoustic phonetics I Peter Ladefoged. - 2nd ed.
p. cm.
Includes bibliographical references and index.
1. Phonetics. Acoustic. I. Title.
P221.5.L33 1996
612.7'8— dc20 95-9057
@The paper used in this publication meets the minimum require-
ments of the American National Standard for Information Sciences--
Permanence of Paper for Printed Library Materials. AN5I 339-43-1992-
CONTENTS
Preface vii
om: Sound Waves 1
TWO Loudness and Pitch 14
nmnn Quality 24
roux Wave Analysis 36
FIVE Resonance 57
srx Hearing 74
SEVEN The Production of Speech 92
am:-rr Resonances of the Vocal Tract 114
Nmra Digital Speech Processing 136
TEN Fourier Analysis 152
susvan Digital Elters and LPC Analysis 181
Iumax 215

___s§§§__.
PREFACE
This is a new edition of Elements of Acoustic Phonetics,
which provided, in seven short chapters, the basic
aspects of acoustics that are important for the study of
speech. A better title for the first edition might have been
"Elements of Acoustics for Phoneticians," as it concen-
trated on acoustics rather than phonetics. The present
book has the same general aim. The basic elements of the
subject have not changed in the forty years since the ear-
lier version was written, so the first six chapters of the
book have been updated only by small changes in tenni-
nology and improved figures, drawn by special-purpose
computer programs that make them more accurate. The
seventh chapter has been expanded so as to take into ac-
count our modem insights into the nature of speech, and
an eighth chapter added that deals with more particular
phonetic issues, such as resonances of the vocal tract and
how formants are related to different cavities. Additional
chapters describe the really new elements that have been
added to acoustic phonetics, due to the use of computers.
Chapter 9 explains how computers store sound waves
and some basic aspects of computer speech processing.
Chapters 10 and 11 go further into computer speech pro-
cessing and are inevitably a little more complicated. But
fill PREFACE
without assuming any more than a vague knowledge of
high school mathematics, they explain the equations
used by computers in the two most common techniques
for the analysis of speech sounds, Fourier analysis and
Linear Predictive Coding.
The aim of the book is still to give an accoumt of just
those aspects of acoustics and digital speech processing
that linguists and phoneficians need to know, without
encumbering them with irrelevant material. Occasion-
ally this has led to some oversimplification or the gloss-
ing over of points that more sophisticated readers might
feel important. I have left them out so that the average
speech scientist or linguist for whom this book is in-
tended does not become daunted by too many techni-
calities.
I have had considerable help in refining this book from
numerous students. My colleagues Pat Keating and
Abeer Alwan have also made helpful comments. I am
particularly indebted to Lloyd Rice, Ned Neuburg, and
Tom Crystal, who taught me much of what I know about
digital signal processing. They suggested good ways of
presenting this material and saved me from some major
infelicities. As always, I am grateful to my wife, Ienny
Ladefoged, for struggling through many drafts and con-
stantly improving the wording of every paragraph (easy
reading is damned hard writing, as P. G. Wodehouse
once said). With all this help, Ihope the book provides a
readable account of the elements of acoustic phonetics
and the basic signal processing techniques used by
computers for speech analysis.
CHAPTER ONE
Sound Waves
O ne of the main difficulties of studying speech is that
sounds are so fleeting and transient. As each word
is uttered it ceases to exist. We can, it is true, recall the
sounds, either by repeating the words or by using some
form of recording. But in both these cases it is another
event that is happening. It is a copy of the original sound,
not the sound itself.
Even during the brief existence of a sound it is curi-
ously difficult to examine it. There is nothing that can be
seen; there is no visible connecting link between a
speaker and a listener. There is air around, but it is not
normally possible to see any changes in the condition of
the air when it is conveying a sound.
Because of these difficulties, it is perhaps best to begin
our study of sound with a brief examination of the hu-
man ear. In this way we start with something tangible,
for we know that the ear is the organ of hearing. Al-
though there is still some uncertainty concerning the
exact mechanism of the ear, we can nevertheless explain
a number of facts about sound in terms of a simplified
theory.
figure 1.1 is a schematic diagram of the essential fea-
tures of the ear. The first part to note is the eardrum,
nerves connected to
auditory sensation area
of the brain
I
bone chain 1
. f /////,4, -_:_:__ I
' J
~. /
- ., / _.;-_.-.
eardrum _ , 4; .'_-232;‘-":_L3:i
\ a J <-. -—" '
‘ "inner ear
filied with liquid
middle ear
I
O Lil! I’ Gil‘
Pig. 1.1. A schematic diagram of the mechanism of the ear.
which is a thin membrane just over an inch down the nar-
row tube, or auditory passage, leading from the outer
ear. When air is pushed down the auditory passage the
eardrum tends to move with it; similarly it moves back as
the air moves away. Connected to the eardrum is a d1ain
of bones whose function is to transmit the movements of
the eardrum to the liquid which is in the inner ear.
Through the action of the bone chain the back»and-forth
vibrations of the eardrum cause vibrations in the liquid.
Closely linked with this liquid are the nerves which lead
to the auditory sensation area of the brain. Movements of
the liquid stimulate these nerves so that we experience
the sensation of hearing. Bringing all these facts together,
we may say that a sound is any disturbance of the air that
could cause a displacement of the eardrum which, after
transmission by the bone chain, could affect the liquid in