Dept. for Speech, Music and Hearing
Quarterly Progress and
Status Report
Speech at high ambient
air-pressure
Fant, G. and Sonesson, B.
journal:
volume:
number:
year:
pages:
STL-QPSR
5
2
1964
009-021
http://www.speech.kth.se/qpsr
1.
Summary
The p r e s e n t s t u d y was i n i t i a t e d a s an attempt t o
g a i n i n s i g h t i n t h e p h y s i o l o g i c a l and a c o u s t i c a l n a t u r e of t h e
t y p i c a l d i s t o r t i o n of d i v e r ' s speech a t deep underwater l e v e l s .
A t a depth of more t h a n 30 m , i.e.
p r e s s u r e s i n a c c e s s of 4 a t a ,
t h e v o i c e a t t a i n s a t y p i c a l " n a s a l " q u a l i t y and s p e c t r o g r a p h i c
a n a l y s i s shows an i n c r e a s e of formant f r e q u e n c i e s and of v o i c e
fundamental frequency,
Harvey
Wathen-DuEn and Cope1 ( 6 ) , Holywell and
( 5 ) , and o t h e r s have d e s c r i b e d t h e s e e f f e c t s but t h e y have
been more concerned with problems of i n t e l l i g i b i l i t y and t h e toxi c e f f e c t s of absorbed g a s e s t h a n w i t h t h e a c o u s t i c problems.
As
f a r a s we know t h e mechanism u n d e r l y i n g t h e " n a s a l q u a l i t y " of
over-pressure
speech has not been s a t i s f a c t o r i l y e x p l a i n e d b e f o r e .
Our s t u d y s t a r t e d with speech r e c o r d i n g s i n t h e decompression chamber of t h e Swedish Marine i n Karlskrona i n 1960
and 1962.
S p e c t r o g r a p h i c a n a l y s i s showed t h a t t h e frequency
s h i f t was p r o p o r t i o n a l l y g r e a t e r i n F, t h a n i n h i g h e r formants.
A simple model of a l i n e a r frequency s h i f t , such a s a s s o c i a t e d
w i t h a change of t h e v e l o c i t y of sound, d i d not f i t t h e s e e x p e r i ments.
Furthermore i t i s known t h a t t h e v e l o c i t y of sound i n a i r
i s almost independent of t h e p r e s s u r e .
The most r e c e n t and c o n c l u s i v e s t u d y was undertaken
i n April 1964 i n t h e decompression chamber on board HMS Belos i n
Stockholm.
The l a t t e r f a c i l i t i e s i n c l u d e an X-ray o u t f i t which
made i t p o s s i b l e f o r u s t o s t u d y t h e v e l a r f u n c t i o n of a s u b j e c t
d u r i n g phonation.
*'The
F r o n t a l and s a g i t t a l X-ray p i c t u r e s showed a
experimental p a r t of t h i s s t u d y was supported by t h e
Swedish Medical Research Council Grant T 312 and W 267
and by a g r a n t f o r speech communication r e s e a r c h from
t h e Swedish Technical Research Council. A summary w i l l
be p r e s e n t e d a t t h e 68th Meeting of t h e B c o u s t i c a l S o c i e t y
,
1964,
of America i n ~ u s t i n / ~ e x a sOctober
normal s t a t u s of t h e velum a t 6 a t a p r e s s u r e .
dlthough these
n e g a t i v e r e s u l t s excluded velo-pharyngeal opening a s t h e main
c a u s s of t h e observed spectrum d i s t o r t i o n , t h e v e r y n a t u r e of
t h i s d i s t o r t i o n s t r o n g l y i n d i c z t e s t h e presence of some kind of
s h u n t i n g mechanism i n v o c a l t r a n s m i s s i o n .
A t h e o r e t i c a l a n a l y s i s h a s now s u p p l i e d c o n c l u s i v e
evidence t h a t t h e s h u n t i n g mechanism i s a s s o c i a t e d w i t h t h e v i b r a t i o n of t h e w a l l s of t h e v o c a l c a v i t i e s , e s p e c i a l l y t h e s o f t p a r t s
of t h e t h r o a t .
A s a by-product
of t h i s s t u d y t h e r o l e of t h e cav-
i t y w a l l s i n normal speech has been emphasized.
These r e s u l t s t i e
i n w e l l w i t h r e c e n t experiments and a n a l y s i s of v o c a l t r a n s m i s s i o n
performed by D r . 0. Fujimura a t t h e Speech Transmission Laboratory.
2.
Spectrographic s t u d y
The r e c o r d i n g of speech i n t h e p r e s s u r e t a n k of HMS
Belos w a s c a r r i e d out w i t h a b a t t e r y operated t a p e - r e c o r d e r and
a dynamic microphone.
A speaking d i s t a n c e of 2 i n c h e s t o t h e
microphone was maintained.
Recordings were made
-tt
I
a t z, i,z.
normal atmosphere p r e s s u r e , and a t 6 a t a , t h e l a t t e r correspondi n g t o 50 meter d i v i n g depth.
A frequency s t a n d a r d t o n e of 1000
c / s was recorded a t each p r e s s u r e l e v e l a s a means of e n s u r i n g
r e l i a b l e frequency c a l i b r a t i o n .
Four s u b j e c t s spoke
l i s t o f CV nonsensz s y l l a -
b l e s comprising a l l p o s s i b l e combinations of C
[ m l , [ n l , [ l ] , [ v 1 9 and V
=
[o:],
[E:]?
=
[b], [dl, [g],
[e:19 [ i : ] ,
[b:]
t o g e t h e r with a s e n t e n c e "I d s g v i l l j a g v i l a p& min 5 " .
R e p r e s e n t a t i v e spectrograms a t 1 and 6 a t a a r e shown
i n Figs. 11-6 t o 11-9, From t h e s e i t i s apparent t h a t a t 6 a t a
F1 i s confined t o a frequency range above a lower l i m i t of
400-500 c / s and t h a t t h e dynamic range of v a r i a t i o n of F, i s much
restricted.
Voiced consonants and t h e vowels [ i ] and [ e l t h u s
o b t a i n almost t h e same F
1
a t very high air-pressures.
Formant f r e q u e n c i e s f o r t h r e e of t h e s u b j e c t s a r e
t a b u l a t e d below.
lata (sub]. N)
sec.
6ata
Fig.
11-6.
Spectrograms of s y l l a b l e s [ v a ] , [ v e l , [ v i ] u t t e r e d
i n a decompressi,on t a n k a t normal atmospheric
,
p r e s s u r e , 1 a t a ( a b o v e ) and 6 a t a (below).
1 a t a (Subi. N.)
6 ato
90
gE
Fig.
11-8,
Spectrograms o f s y l l a b l e s [ g o : ] , [ge
a t 1 and 6 a t a p r e s s u r e .
g fl
:I, [gi:]
"-
A ' . l ' A.
' I '
.3 .
I
I '
.k ' .I6 ' .7I ' -8
J ' l ' l ' l ' ~ ' l ' ~ ' l ' l ' l " ' " "
la 11 1.2 1. 1L 1 1.6 1.7 1.8 1.9 2.0 2.1 set.
.
1 a t a (Subi.N.)
6 ata
90
gE
Fig. 11-8,
Spectrograms of s y l l a b l e s [go:],
a t 1 and 6 a t a p r e s s u r e .
GI Pi
[ge:]
,
[gi:]
sec
Fig.
11-9.
S p e c t r o g r a m o f a s a m p l e o f c o n n e c t e d speech
" I d a g v i l l j a g v i l a " a t 1 and 6 a t a .
TABLX 11-1
Formant frequencies a t 1 and 6 a t a
Vowel
Subject
1---1 ata
[o:
I
[E:
I
16 ata/
-4-r1 a t a ' 6 ata
A
[+: I
[a:I
[e: I
[i: 1
Ru = Rundblom
Ni
=
Nilsson
Ga = Garner
Samples were t a k e n at t h e middle o r t e r m i n a l p a r t of
t h e vowel whichever seemed more s t a t i o n a r y i n formant frequency
pattern.
Data f o r a l l consonantal environments have been averaged
i n Table 11-1.
The d a t a on F
3
have been excluded i n i n s t a n c e s
where t h e y were judged t o be l e s s r e l i a b l e .
The s e r i e s N i I and
N i I1 p e r t a i n t o t h e s u b j e c t N i a t two d i f f e r e n t occasions.
There a r e t y p i c a l t r e n d s t o be observed.
The F l - s h i f t
i s w i t h few e x c e p t i o n s g r e a t e r i n magnitude t h a n t h e s h i f t s i n F2
and F
3'
I n vowels [ d l and [ i ] t h e observed F 2 - s h i f t s a r e of t h e
same o r d e r of magnitude a s t h e s t a n d a r d d e v i a t i o n , 50 c / s , o r l e s s .
It i s i n t e r e s t i n g t o n o t e t h a t t h e d i s t i n c t i o n between t h e F1 of
[i] and [ e l tended t o be e l i m i n a t e d a t t h e h i g h p r e s s u r e f o r subj e c t s N i and Ru and t h a t a c c o r d i n g l y t h e a u d i t i v e d i s t i n c t i o n between t h e s e phonemes was almost l o s t .
The t y p i c a l d i s t o r t i o n of back vowels [ o ] and [ Q ] at
h i g h p r e s s u r e s i s t h a t of a r a i s e i n both FA and F2 but g e n e r a l l y
more i n F1 so t h a t F, comes r a t h e r c l o s e t o F2.
These a t t r i b u t e s
account f o r t h e e s p e c i a l l y apparent n a s a l q u a l i t y of t h e vowel
[ Q 1. Two of t h e f o u r speakers showed a moderate i n c r e a s e i n
v o i c e fundamental frequency Fo.
Subject
Average F
0
1 ata
6 ata
Ru
124
124
Ni
114
132
Ga
127
163
An
187
182
Other g e n e r a l o b s e r v a t i o n s of speech a t h i g h p r e s s u r e s
a r e an i n c r e a s e i n o v e r a l l sound p r e s s u r e l e v e l of v o i c e d sounds
and a r e l a t i v e l o s s of spectrum i n t e n s i t y l e v e l a t h i g h frequencies.
There i s a pronounced weakening of t h e energy of a l l un-
v o i c e d consonants e s p e c i a l l y of t h e b u r s t i n t e r v a l of s t o p sounds.
Mo a c t u a l measurements of formant bandwidths were undertaken but
t h e g e n e r a l o b s e r v a t i o n from t h e broad-band
spectrograms was t h a t
bandwidths d i d not i n c r e a s e except i n t h e low F1-range.
s p e a k i n g tempo was s u b s t a n t i a l l y reduced.
The
Some but not a l l of t h e
s p e a k e r s showed t y p i c a l s i g n s of d i s t u r b e d v o i c e s o u r c e mechanism
i n terms of a randomization of subsequent p i t c h p u l s e p o s i t i o n s
and a g e n e r a l " n o i s i n e s s " superimposed on t h e spectrogram.
3.
Theory
It i s of i n t e r e s t t o n o t e t h a t o b s e r v a t i o n s of q u i t e
o p p o s i t e s i g n s have been made on speech at h i g h a l t i t u d e s .
K.C.
C l a r k e t a 1 ( 2 ) r e p o r t e d a r e d u c t i o n of t h e f r e e f i e l d sound
p r e s s u r e l e v e l of v o i c e d sounds of t h e o r d e r of 10 dB a t 35000
f e e t a l t i t u d e , w h i l s t t h e sound p r e s s u r e l e v e l of unvoiced consonants increased
5 dB and t h u s gained
15 dB r e l a t i v e t o voiced-sounds.
h l a c k of n a s a l i t y was pronounced.
Thus t h e r e i s a c o n s i s t e n t s e t of v a r i a t i o n s of observed a c o u s t i c c h a r a c t e r i s t i c s a s a f u n c t i o n of t h e a i r - p r e s s u r e ,
i.e.
t h e d e n s i t y from deep underwater t o h i g h a l t i t u d e c o n d i t i o n s .
-a. - -F r-e ~ e n c g-s h-i f-t s
Since d e n s i t y p
i s p r o p o r t i o n a l t o p r e s s u r e P the
v e l o c i t y of sound
i s dependent on y , t h e r a t i o of s p e c i f i c h e a t s a t c o n s t a n t p r e s s u r e
and volume, only.
w i t h e0.7
A change of P from 1 a t a t o 6 a t a i s a s s o c i a t e d
'$ change i n y (1.407 t o 1.417), and t h u s merely 0.35 %
i n c.
S i n c e a l l e q u a t i o n s f o r c a l c u l a t i n g resonance frequenc i e s of an a r b i t r a r i l y complex v o c a l c a v i t y system c o n t a i n t h e
f a c t o r c and i n a d d i t i o n f u n c t i o n s of c a v i t y dimensions only, it
i s obvious t h a t t h e d e t u n i n g of c a v i t y resonances a s a r e s u l t of
a change i n a i r p r e s s u r e e n t e r s through c a l o n e and i s i n s i g n i f i c a n t l y small.
Thus t h e e x p r e s s i o n f o r t h e resonance frequency of
a Helmholtz resonance i s
where V i s t h e volume, A t h e c r o s s - s e c t i o n a l a r e a of t h e neck and
le i t s e f f e c t i v e l e n g t h .
The f r e q u e n c i e s of s t a n d i n g wave
resonances i n a t u b e t e r m i n a t e d d i f f e r e n t l y at t h e two ends (open
c i r c u i t a t one end and s h o r t c i r c u i t a t t h e o t h e r ) a r e
F
n
=
(2n-I )
41,
C
(3)
and when t e r m i n a t e d e q u a l l y at both ends,
F = - C* n
n
21
Now t o t h e e f f e c t of a f i n i t e c a v i t y w a l l impedance.
It was o r i g i n a l l y p o s t u l a t e d by van den Berg
('I
that the soft
p a r t s of t h e v o c a l c a v i t y w a l l s behave l i k e a mass element t o t h e
f i r s t approximation w i t h a r e s i s t i v e element t o account f o r d i s s i I n Fig. 11-1 0 t h e e q u i v a l e n t network elements of t h e
pation.
c a v i t y w a l l s a r e denoted L
W
and Rw.
The r a d i a t i o n impedance i s
denoted Roe
Assuming t h a t t h e v i b r a t i n g w a l l s occupy an a r e a of
Aw
3
50 cm
of 80 cm
2
2
a l o n g a pharynx l e n g t h of 8 cm and an i n t e r n a l volume
r e p r e s e n t a t i v e of a p a l a t a l tongue p o s i t i o n , t h e pharynx
w a l l inductance i s
where p w
9
1 g/cm3
i s t h e d e n s i t y and 1 = 1 cm i s t h e average
W
t h i c k n e s s of t h e w a l l s .
A t complete c l o s u r e of t h e v o c a l t r a c t t h e mass element
LW r e s o n a t e s with t h e c a p a c i t a n c e C of t h e e n t i r e a i r volume.
The
l i m i t i n g resonance frequency i s t h u s
a s assumed above, and
-where Lw A
W
A t a p r e s s u r e of 1 a t a and normal s p e a k i n g c o n d i t i o n s
3
c = 35000 cm/sec and p = pl = 1.2
A t a pressure of
g/cm
.
P a t a t h e d e n s i t y i s p = P e p I and the l i m i t i n g v a l u e of F,
is
which amounts t o
Thus at P = 6 a t a t h e fundamental resonance F1 must exceed 370 c / s ,
which conforms with our o b s e r v a t i o n s .
It i s a l s o known t h a t t h e
"voice b a r t t F, of v o i c e d consonants never goes below 150 c / s i n
normal speech.
The f i r s t formant of a voiced consonant o r of a c l o s e
o r half-open vowel i s a p p a r e n t l y tuned by LW i n p a r a l l e l w i t h L1.
I f , f o r example, L1
=
Lw, F~ would e q u a l
Si-
F~~ = 2 1 0 c / s .
In
g e n e r a l d e n o t i n g t h e resonance of t h e system with Lw excluded a s
F l a y and F1 with due r e s p e c t t o both L1 and Lw, and Flw w i t h L,
excluded t h e r e h o l d s t h e r e l a t i o n
A t a p r e s s u r e of P t h i s may be w r i t t e n
By combining e q u a t i o n s of t h i s t y p e f o r P
=
1 dnd P
=
6 a t a we
obtain
which r e l a t e s t h e fundamental resonance of t h e c l o s e d v o c a l t r a c t
at
Flw(~.l ) t o t h e observed f r e q u e n c i e s of t h e f i r s t formant
F I 6 a t P = 6 a t a , and F l l a t P = 1 a t a .
I f t h e t h e o r y h o l d s i t should be p o s s i b l e t o c a l c u l a t e
r e a s o n a b l e v a l u e s of Flw a t 1 a t a from t h e observed frequency
shifts.
C a l c u l a t i o n s on o u r m a t e r i a l gave t h e f o l l o w i n g d a t a :
F i g . 11-10.
A.
T r a n s m i s s i o n l i n e a n a l o g of t h e v o c a l t r a c t w i t h
d i s t r i b u t e d i n d u c t a n c e ~ ( x ) c, a p a c i t a n c e ~ ( x ) and
,
w a l l i n d u c t a n c e L ~ ( Xp)e r u n i t l e n g t h of t h e r e s o n a t o r a t a c o o r d i n a t e x.
B.
Helmholtz r e s o n a t o r w i t h t c t a l i n d u c t a n c e Lw and
r e s i s t a n c e R,, of t h e c a v i t y w a l l s i n c l u d e d .
Ro
i s the radiation resistance.
C.
E q u i v a l e n t c i r c u i t of B f o r c a l c u l a t i o n of F,
of v o i c e d c o n s o n a n t s and c l o s e f r o n t vowels.
where w W i s t h e c u t o f f frequency
With n o t a t i o n s A f o r c r o s s - s e c t i o n a l a r e a of t h e r e s o n a t o r and
As f o r t h e a r e a p e r u n i t l e n g t h of t h e v i b r a t i n g w a l l of t h i c k n e s s
ds and d e n s i t y
p
f
thus
The c u t o f f frequency
sir p
, or
W
i s p r o p o r t i o n a l t o t h e d e n s i t y of t h e
t o the pressure P i n ata.
Under t h e s p e c i a l circum-
s t a n c e s of a uniform d i s t r i b u t i o n of t h e wall impedance a l o n g a
s i n g l e t u b e model i t i s found t h a t ww = 2wFl
A s a s p e c i f i c example assume a pharynx l e n g t h of 8 cm
and a high p r e p a l a t a l a r t i c v . l s t i o n i n which c a s e F p of [ i ] could
be approximately c a l c u l a t e d a s
The c s v i t y w a l l c o r r e c t i o n f a c t o r a t 1 a t a i s 0.26 $ which i s negl i g i b l e and 1.6
37
-
6
% o r 37 c / s a t
P = 6 ata.,
The c a l c u l a t e d d i f f e r e n c e
31 compares well with t h e measured d a t a .
=
A s a n o t h e r example t h e v o c a l t r a c t w i l l be considered
a s a s i n g l e homogeneous tube loaded w i t h d i s t r i b u t e d w a l l inductance
and u
=
W
21-rolGO
f0rmar.t F
1
=
before.
Assuming a frequency of t h e Sirst
c/41e = 500 c / s t h e a d d i t i o n of Ls c a u s e s a s h i f t of
AF1 = 1 3 5 c / s a t 6 a t d which l l s o r e f l e c t s t h e c o r r e c t o r d e r of
magnitude a c c o r d i n g t o measurements,
I n s h o r t t h e e f f e c t s d e s c r i b e d above a r e a t t r i b u t a b l e
t o t h e h i g h d e n s i t y p i n c r e a s i n g t h e c h a r a c t e r i s t i c impedance l e v e l
p c / ~of t h e v o c a l c a v i t y s y s t e ~a t h i g h a i r - p r e s s u r e s
t h u s making
t h i s system more s u s c e p t i b l e t o t h e s h u n t i n g e f f e c t s of t h e c a v i t y
w a l l s , t h e l a t t e r b e i n g independent of t h e a i r - p r e s s u r e .
The in-
c r e a s e of t h e a i r column l o a d i n s e r i e s with t h e mechanical i m pedance of t h e v o c a l f o l d s could account f o r t h e phonatory source
d i s t u r b a n c e s observed.
There remains t o map t h e r e l a t i v e c o n d u c t i v i t y of t h e
c a v i t y walls.
Thin f l e s h obviously h a s a more s e v e r e s h u n t i n g ef-
f e c t t h a n bony and t h i c k s t r u c t u r e s ,
One would t h u s p r i m a r i l y
conceive of t h e s i d e s of t h e t h r o a t and t h e cheeks of t h e mouth
t o permit v i b r a t i o n s but a l s o t h e s o f t velum i t s e l f .
The r e l a t i v e
i n f l u e n c e of a shunt on t h e frequency of v o c a l resonance i s a l s o
dependent on t h e s p a t i a l d i s t r i b u t i o n of sound p r e s s u r e i n t h e
vocal t r a c t .
I n t h e frequency range of t h e f i r s t formant a c a v i t y
wall shunt i s t h u s t h e more e f f e c t i v e t h e c l o s e r i t comes t o t h e
I n g e n e r a l t h e e f f e c t of a shunt i s
g l o t t a l end of t h e system.
l a r g e wherever t h e sound p r e s s u r e i s high.
bandwidths
-b. - -Formclnt
------A t h e o r e t i c a l s t u d y of t h e e x t e n t t o which t h e d e n s i t y
of a i r e n t e r s e x p r e s s i o n s of formant bandwidth can be made from
,
r e f . ( 3 1 pp. 300-310.
The c o n c l u s i o n i s t h a t bandwidths a r e a l -
ways r e l a t e d t o e x p r e s s i o n s of t h e form R / ~ Lo r I / ~ ~ R c . Acoustic
inductance a s well a s r e s i s t a n c e , even t h e r a d i a t i o n r e s i s t a n c e ,
a r e p r o p o r t i o n a l t o d e n s i t y and a c o u s t i c c a p a c i t a n c e i s i n v e r s e l y
proportional t o density.
Thus d e n s i t y i s c a n c e l l e d out i n a l l
e x p r e s s i o n s above.
Xnergy l o s s e s a s s o c i a t e d w i t h v o c a l c a v i t y v i b r a t i o n s
z r e of a g r e a t e r i n t e r e s t .
Recently Fujimura has determined t h o
c l o s e d c o n d i t i o n resonance F
of t h e vocal t r a c t e x p e r i m e n t a l l y
Iw
and found f r e q u e n c i e s of t h e o r d e r of 150-200 c / s and bandwidths
of t h e o r d e r of 100 c/s.
ance element R
W
The bandwidth i s a t t r i b u t e d t o a r e s i s t -
i n s e r i e s with t h e w a l l inductance L
as in
W
Fig. 11-10 and we t h u s conclude t h a t
A t formant f r e q u e n c i e s of i n t e r e s t fvLw > R,
and w e compute a
parallel resistance
With a f i n i t e mouth opening of inductance
L, p a r a l l e l t o LW we
have approximately
But
The c o n t r i b u t i o n of c a v i t y wzll d i s s i p a t i o n t o f i r s t formant bandwidth B 1 i s t h u s i n v e r s e l y p r o p o r t i o n a l t o t h e square of frequency,
1
which i s of t h e ordez
I f f o r example L1 = LW and F1 = ,/ 2
FI0
of 225 c / s , t h e bandwidth c o n t r i b u t i o n i s
o r d e r of 50 c/s.
B,
=
Bw/2 o r of t h e
The formant d a t a of Fujimura, r e f .
t h i s frequency dependency of B1.
F, = 500 c / s of about B1
(4
confirms
Normally B,, ( f ) has a minimum a t
= 30 c / s .
A t t h e h i g h e r atmospharic p r e s s u r e s t h e o n l y s i g n i f i -
c a n t change of t h e e q u i v a l e n t c i r c u i t i s t h e d e c r e a s e of t h e capaci t a n c e of t h e a i r and t h u s t h e i n c r e a s e i n resonance f r e q u e n c y ,
w h i l s t t h e bandwidth i s t h a t of t h e corresponding resonance a t t h e
lower p r e s s u r e , i.2.
assuming F
Iw
lower frequency.
= 160 we t h u c have F16
At L,
=
=KO
f?
LW and P
160 =
=
555
6 ata
and
= Bw/2 = 50 c / s .
I n a d d i t i o n t h e r e i s t h e r a d i a t i o n 2nd i r i c B1 6
t i o n a l damping adCing sone 10-20 c / s more t o B,. Spectrograms
confirm t h e t h e o r y .
A t 6 a t a t h e v o i c e bar F1 of v o i c e d consonants
i s a frequency t r a n s p o s e d r e p l i c a of t h o 160 c / s v o i c a b a r a t 1 a t a
with t h o weak and t h i n v o i c i n g s t r i a t i o n s t y p i c a l of a l a r g e bandwidth formant.
e ss ur e -l e vels
-c . - -Sound
- - prA p o s i t i v e s h i f t of a formant of c o n s t z n t bandwidth i s
a s s o c i a t e d with an i n c r e a s e of i t s Q and of t h e spectrum l e v e l a t
.
f r e q u e n c i e s above F.,
This i s one f a c t o r c o n t r i b u t i n g t o an in-
c r e a s e of sound p r e s s u r e l e v e l s st h i g h e r ambient p r e s s u r e s .
It
a f f e c t s p r i m a r i l y voiced sounds of a narrow a r t i c u l a t i o n .
There 3 r e a l s o r e a s o n s f o r e x p e c t i n g an o v e r a l l inc r e a s e of t h e i n t e n s i t y of v o i c e d sounds because of more e f f i c i e n t
radiation.
The b a s i s f o r t h i s c o n s i d e r s t i o n i s a phonation a t
constant s u b g l o t t a l overprzssure
Ap,
According t o r e f . ( 3 ) 9 P*
268, t h e volume v e l o c i t y of t h e source i s
\iG-
U (t)= ~ ( t )
a
uo .(
To t h i s we add t h e v o c i l t r a c t t r a n s f e r f u n c t i o n ~ ( w )=
and t h e r a d i a t i o n t r a n s f e r
q7-a
( u ) / u ~r e l a t i n g sound p r e s s u r e a t
1 cm i n f r o n t of t h e speaker t o t h e volume v e l o c i t y st t h e l i p s ,
,/
-
1
.
Thus t h e sound p r e s s u r e p ( w ) i s p r o p o r t i o n a l t o
p or t o 4 P
1
A f a c t o r of
= , F f r o m P = 1 t o 6 a t 3 ) would t h u s cause an in-
,E
c r e a s e of t h e sound p r e s s u r e l e v e l of ~ 6 ' o r8 dB1
Our e x p e r i -
mental d a t ~from HMS Belas showed an i n c r e a s e of on t h e average
5 dB, but t h i s
i s not c o n c l u s i v e s i n c e t h e microphone d i s t a n c e was
not s u f f i c i e n t l y w e l l c o n t r o l l e d .
Sounds of low F, gained much
more t h a n sounds of h i g h PI a s c o u l d bs conceived from theory.
-d. - -Unvoiced
- - - -sounds
--What i s t h e r s a s o n f o r t h e decreased r e l a t i v e l e v e l of
s t o p b u r s t s and f r i c d t i v e s a t high ambient p r e s s u r e s ?
Here t h e
t h e o r y i s not s o w e l l developed but i t may be of i n t e r e s t t o r e f e r
t o p. 273 of r e f . ( 3 )
.
The sound p r e s s u r e of f r i c a t i v e s i s propor-
t i o n a l t o t h e square of t h a v e l o c i t y of t h e g e n e r a t i n g
a i r strean
i n a v o c a l t r a c t c o n s t r i c t i o n o The r e l a t i o n of t h i s a i r v e l o c i t y
u
= U
0
/A t o t h e p r e s s u r e drop
where k i s a c o n s t a n t .
4 p is
.
Again assuming a c o n s t a n t Ap t h e U 2 1s
0
inversely proportional t o
T h i s c f f e c t i s probably counter-
p.
a c t e d by t h e p p r o p o r t i o n a l i t y of t h e r a d i a t i o n t r a n s f e r , eq. ( 2 4 ) .
A t h i g h ambient a i r - p r e s s u r e s
t h e r e remains a d e c r e a s e of t h e
sound p r e s s u r e l e v e l of f r i c a t i v e s dnd s t o p s r e l a t i v e t o t h e
average l e v e l of v o i c e d sounds.
G o Fant and B. SonessorPC
References:
(1 )
van den Berg, Jw. : Physica van dc stemvorming met
t o e a s s i n p e n , t h e s i s Univ. of Groningen
eg- 1953).
(2)
C l a r k , K.C.,
Rudmose, H.W., E i s c n s t e i n , J . C . ,
C a r l s o n , F.D.,
and Walker, R,A.:
"The e f f e c t s of high a l t i t u d e
20 (1 9 4 8 ) , pp. 776-786.
on speech", J.Acoust .Soc.Am. -
(3)
Fctnt
, G.
I
Acoustic Theory of Speech P r o d u c t i o n ,
( ' s - ~ r ~ v e n h a g e1960),
,
J, s "The sinewave response
of t h e v o c a l t r a c t " , STL-QPSH 1/1964, pp. 5-1 0.
( 4 ) Fujimura, 0. and Lindqvist
( 5 ) Holywell, K. and ilarvey,
Soc.Am,
(6)
36
G.:
"Helium speech", J . k c o u s t .
( 1 9 6 4 ) ~p* 2100
Wathen-hnn, W. 2nd Copel, M.:
"Comparison of v o i c i n g
p e r i o d i c i t i e s and formant f r e q u e n c i e s f o r one speaker
i n a i r and i n 3 helium-oxygen mixture a t v a r i o u s
p r e s s u r e s " , J .Acous-t ,Sot ,Amo 2 ( 1 963), p. 804 (A).
* Department
of Annt omy, TJniversity of Lund, Sweden, and
t h e O f f i c e of t h e Surgeon General, Naval S t a f f , R.S.N.,
Stockholm, Sweden.