Table Of ContentSpringer Series in Information Sciences 35
Springer-Verlag Berlin Heidelberg GmbH
Springer Series in Information Sciences
Editors: Thomas S. Huang Teuvo Kohonen Manfred R. Schroeder
30 Self-Organizing Maps
By T. Kohonen 2nd Edition
31 Music and Schema Theory
Cognitive Foundations of Systematic Musicology
By M. Leman
32 The Maximum Entropy Method
By N. Wu
33 A Few Steps Towards 3D Active Vision
By T. Vieville
34 Calibration and Orientation of Cameras in Computer Vision
Editors: A. Grün and T. S. Huang
35 Computer Speech
Recognition, Compression, Synthesis
By M. R. Schroeder
Volumes 1-29 are listed at the end of the book.
Manfred R. Schroeder
Computer Speech
Recognition, Compression,
Synthesis
With Introductions to Hearing and Signal Analysis
and a Glossary of Speech and Computer Terms
With 78 Figures
Springer
Professor Dr. Manfred R. Schroeder
Drittes Physikalisches Institut
Universität Göttingen
Bürgerstrasse 42-44,
0-37073 Göttingen, Germany
Series Editors:
Professor Thomas S. Huang
Department of Electrical Engineering and Coordinated Science Laboratory ,
University of Illinois, Urbana, IL 61801, USA
Professor Teuvo Kohonen
Helsinki University of Technology, Neural Networks Research Centre, Rakentajanaukio 2 C,
FIN-02150 Espoo, Finland
Professor Dr. Manfred R. Schroeder
Drittes Physikalisches Institut, Universität Göttingen, Bürgerstrasse 42-44,
0-37073 Göttingen, Germany
Excerpts from Music Perception, IEEE Proceedings, and Cartoons
from The New Yorker reprinted with permission.
ISSN OnO-678X
ISBN 978-3-662-03863-5 ISBN 978-3-662-03861-1 (eBook)
DOI 10.1007/978-3-662-03861-1
Library of Congress Cataloging-in-Publication Data applied for.
Die Deutsche Bibliothek - CIP-Einheitsaufnahme
Sehroeder, Maufred R.:
Computer speech: recognition, compression, synthesis; with introductions to hearing and signal analysis
and a glossary of speech and computer terms / Manfred R. Schroeder. - Berlin; Heidelberg; New York;
Barcelona; Hong Kong; London; Milan; Paris; Singapore; Tokyo: Springer, 1999
(Springer series in information sciences; 35)
This work is subject to copyright. All rights are reserved, wh ether the whole or part of the material is concerned.
specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on
microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is
permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version,
and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under
the German Copyright Law.
© Springer-Verlag Berlin Heidelberg 1999
Originally published by Springer-Verlag Berlin Heidelberg New York in 1999.
Softcover reprint of the hardcover 1s t edition 1999
The use 01' general descriptive names, registered names, trademarks, etc. in this publication does not imply, even
in the absence of a specific statement, that such names are exempt from the relevant protective laws and
regulations and therefore free for general use.
Typesetting: Data conversion by Satztechnik Katharina Steingraeber, Heidelberg
Cover design: design & productilm GmbH, Heidelberg
SPIN: 10676879 56/3144 -5 432 I 0 -Printed on acid-free paper
To Anny
Marion, Julian, Alexander
Marion, Uwe
Julia, Lilly, N ora, Nicola
Preface
World economies are increasingly driven by research, knowledge, information,
and technology - with no small part being played by computer speech:
• automatie speech recognition and speaker authentication,
• speech compression for mobile phones, voice security and
Internet "real audio,"
• speech synthesis and computer dialogue systems.
According to the London Economist information technology represents "a
change even more far-reaching than the harnessing of electrical power a cen
tury aga ... Where once greater distance made communieations progressively
more expensive and complicated, now distance is increasingly irrelevant." 1
Natural speech, predominant in human communication since prehistorie
times, has acquired a brash new kin: synthetie or computer speech. While
people continue to use speech liberally, many of us are increasingly exposed to
speech manufactured and understood by computers, compressed or otherwise
modified by digital signal processors or microchips. This evolution, driven by
innumerable technieal advances, has been described in a profusion of scientific
papers and research monographs aimed at the professional specialist. The
present volume, by contrast, is aimed at a larger audience: all those generally
curious about computer speech and all it portends for our future at home
and in the workplace. I have therefore kept the technical details in the first
chapters to a minimum and relegated any unavoidable "mathematics" to the
end of the book.
Considering the importance of hearing for speech compression, speech
synthesis (and even recognition), I have included abrief overview of hearing,
both monaural and binaural.
I have also added a compact review of signal analysis because of its rele
vance for speech processing.
For the benefit of readers new to speech and computers I have added
a glossary of terms from these fields. I have also augmented the numbered
references by a list of books for general reading, selected journals, and major
meetings on speech.
1 Frances Cairncross, The Economist, 13 September 1997. Quoted from The New
York Review of Books, 26 March 1998 (p.29). But see also Thomas K. Landauer,
The Trouble with Computers (MIT Press, Cambridge, MA 1995).
VIII Preface
Progress in any field does not arise in a vacuum but happens in a manifestly
human environment. But many scientists, Carl Friedrich Gauss, the "Prince
of Mathematicians" foremost among them, take great pride in obliterating in
their publications any trace of how success was achieved. From this view, with
all due respect for the great Gauss, I beg to differ. Of course, in mathematics,
the "conjecture - lemma - theorem - proof" cycle will always remain the
mainstay of progress. But I believe that much is to be gained - and not only
for the nonspecialist - by putting scientific advances in a personal context.
Some Personal Recollections
This book has its genesis in a visit by a Bonn linguist to the University of
Göttingen in Germany shortly before Christmas 1951. The noted speech sci
entist had been invited to give a talk at the General Physics Colloquium, not
on the usual nuts-and-bolts exploits in physics, but on Shannon's communi
cation theory and its potential importance for human language, written or
spoken.
After the distinguished guest had safely departed, most of the physicists
present professed "not to have understood a word." During the ensuing de
part mental Christmas party the chairman, the reigning theoretical physi
eist, asked me how I had liked the lecture. When ladmitted that (although
far from having understood everything) I was deeply impressed, the profes
sor's answer was a disapproving stare. How could anything be interesting, he
seemed to be saying, that did not partake of Planck's quantum of energy or
general relativistic covariance.
I was working on concert hall acoustics at the time, using microwave
cavities as a convenient model for acoustic enclosures. I was so on astounded
by the chaotic distribution of the resonances that my measurements revealed
- even for relatively small deviations from perfeet geometrie symmetry of the
cavity: I had stumbled on the very same probability distribution that also
governs the energy levels of complex atomic nuclei and that Eugene Wigner in
Princeton had already promulgated in 1935. But at that time and for decades
thereafter few (if any) physicists appreciated its general import.
Now, 60 years later, the Wigner distribution is recognized as a universal
tell-tale sign of "non-integrable" dynamical systems with chaotic behavior.
But, of course, chaos hadn't been "invented" yet and I for one didn't know
enough nuclear physics - too much like chemistry I thought - to see the
connection. Nor, I think it is safe to say, did atomic physicists know enough
about concert halls or microwave cavities to appreciate the common thread.
Interestingly, the Wigner distribution also raises its head in - of all things -
number theory, where it describes the distribution of the (interesting) zeros
of the Riemann zeta-function.
Be that as it may, my thesis advisor was much impressed by my progress
and suggested that I go to America, the "microwave country." The thought
Preface IX
had crossed my mind and it did sound interesting. So I applied for a Fulbright
Fellowship - and failed flat out. My academic grades were good, my English
was passable but, the Fulbright commission concluded, I was not politically
active enough. They were looking for foreign students who, upon their return
from the States, could be expected to "spread the gospel" about democracy,
the American Way of Life and so forth. But I, it seemed, was mostly interested
in physics, mathematics, languages, photography, tennis and - perish the
thought - dancing.
During my thesis on the statistical interference of normal modes in microwave
cavities and concert halls, I discovered the work of S. O. Rice on random
noise, which explained a lot about sound transmission in concert halls. 2
Now Rice, I knew, was with Bell and so was Shannon. So after my Ful
bright failure I went to my professor and asked hirn for a recommendation
for Bell Laboratories. But he told me that Bell didn't take any foreigners. In
fact, in 1938 he had backed one of his better students (who was eager to leave
Germany) but Bell declined. (I still wonder what was behind that rejection.)
Then, in early 1954, James Fisk (later president of Bell Laboratories)
and William Shockley (of transistor farne) traveled to Germany (Fisk had
studied in Heidelberg) to look for young talent for Bell. When I heard about
this, I immediately went again to my professor telling hirn that Bell was
not only accepting foreigners but they were actively looking for them. This
time around the kind professor promised a recommendation and just three
weeks later I received an invitation from Bell for an employment interview in
London.
An U nusual Interview
The venue of the interview was the lobby of the Dorchester Hotel. After
explicating my thesis work, I asked the recruiter to tell me a bit about the
Bell System. "WeIl, there was AT&T, the parent company, Western Electric,
the manufacturing arm, Bell Laboratories, and 23 operating companies: New
York Telephone, New Jersey Bell, Southern BelL .. " when, in the middle
of this recitation, he stopped short and, with his eyes, followed an elegant
young lady (an incognito countess?) traversing the long lobby. After aminute
2 It transpired that such transmission functions were basically random noise, albeit
in the frequency domain, and that room acousticians, for years, had measured
nothing but different sampIes of the same random noise in their quest for a
formula to pinpoint acoustic quality. Within a limited cohort of acousticians I
became quite wellknown for this work although it was just an application of
Rice's theory. But it did establish a new area of research in acoustics (and later
microwaves and coherent optics): random wave fields, with many interesting ap
plications: acoustic feedback stability of hands-free telephones and public address
systems, fading in mobile communications and laser speckle statistics.
X Preface
or two, without losing a beat, he continued "yes, and there is Southwestern
Bell, Pacific Telephone, ... "3
Everything went weIl during the interview, and I so on received an offer of
employment. The monthly salary was $640 - five times as much as a young
Ph.D. could have made at Siemens (500 Marks). But, of course, at Bell I
would have worked for nothing.
On September 30, 1954, arriving in New York, I stepped off the Andrea
Doria (still afloat then) and into a chauffeured limousine which took me
and my future director and supervisor to one of the best restaurants in the
area. I couldn't read the menu (mostly in French) - except for the word
Bratwurst. So, with champagne corks popping and sparkling desserts going off
at neighboring tables, everybody in our party had Bratwurst and Löwenbräu
beer (my future bosses were obviously very polite people) - I wonder how
many immigrants were ever received in such style.
Arriving at the Murray Hill Labs, I was put on the payroll and given a
dollar bill as compensation for all my future inventions. (When I retired 33
years later I had garnered 45 V.S. patents and innumerable foreign filings,
but the fact that I had earned less than 3 cents for every invention never
bothered me.)
Once securely ensconced at Murray Hill, I was encouraged to continue my
work on random wave fields but - in typical youthful hubris - I thought I
had solved all relevant problems and I elected to delve into speech. Speech,
after all , meant language - always a love of mine - and possibly relevant to
the telephone business.
The Bachelor and the Hoboken Police
William H. Doherty, my first Executive Director at Bell, introduced me to
one and all as "Dr. Schroeder, who just joined us from Germany - and he
is a bachelor." I was 28 then but apparently already getting a bit old for
a single Catholic male. (I later had to disappoint Bill by marrying in an
interdenominational ceremony - at the Chapel of the Riverside Church on
the Hudson - my wife being Orthodox.)
When one night, carrying a camera with a very long lens, I was arrested by
dockworkers on the Hoboken piers (believing they had caught a foreign spy),
3 Twenty-five years later, to the day, on April 25, 1979, I went back to the Dor
chester. At the far end of the lobby there was a kind of hat-check counter with an
elderly lady behind it. I went up to her and asked "Could it be that on this day,
25 years ago, on April 25, 1954, a Sunday, a young woman might have appeared
from the door behind you - it was about 2 p.m. - crossed the lobby and then
exited by the revolving door?" She must have thought I was from Scotland Yard
or something. But, unflustered, she answered "Oh yes, of course, at 2 p.m. we had
a change of shifts then. This entrance was for service personnel - chambermaids
and so forth." I asked her, "How do you know this?" And she said, "I have been
here for 30 years."
