Dept. for Speech, Music and Hearing

Quarterly Progress andStatus Report

Physiological studies ofspeech

Ladefoged, P.

journal: STL-QPSRvolume: 2number: 3year: 1961pages: 016-021

http://www.speech.kth.se/qpsr

I11 SPEXCH PRODUCTION

A . PHYSIOLOGICAL STUDIES OF SPSECZ

A sys ten f o r recording sub-glot ta l prcssuro h-n bscn s e t

up, It i s essentially the same a s thc systems i n use i n thc Phcnetics

and Physiology Departments of the U n i v ~ ~ s i t y of Edinb,~rgh (' ) a;J the

Communication Scicnccs Labor~~ to ry , Universi ty of Michigan* Tho sv.3-

joct passes a ca thc tc r with 2 s n a l l balloon on t h c cnd throvgh 5ho

nose down i n t o thc oesophagus t o 2 point s l i g h t l y abou? -;kc 1 ~ x 7 2 1 oy

the b i furca t ion of the trschca; t h i s i s about 34 cm f r o 3 tl:o astcrilal

nares i n a cubject 1.8 m tall. Tlie pressurc changes j.n the b~l loor ! .

a r e now transduccd by ari Elcmr, sLrein gaugc. t r a n s d u c ~ ~ . , 2-ncl rczordcd

on 2 Mingograph. The freq.ucacy rcs3onse of the whole system hzs boen

measured by s c a l i n g the ca the tor and balloon i n an e n c l 9 s ~ r c fi"osl?cd

by a bozrd screwed against l o u i s p e ~ k c r . Thc louOspcekcr was dri-re11

with a constant amplitudc ( a s chcckcd by a capac i tor nicrophonc scaled

i n t o thc same enclosure) ovcr a Trequency range of 20-300 c/s. Uzinc

a balloon 1.5 cm i n d ianc ter 2nd 2 cn long, scaled t o thc astroxc c ~ d

of a polythenc c a t h e t e r 4,5 cm lone, and with an in tern21 c?i?illctcr of

4 mm, thc system had zn ecoust ic resonzncc a t 120 c / s , This, p2zic wzs

e f fec t ive ly dempcd out by packing a b m t 4 cm of the cathcfer :5 :h P i i ~ c

s t e e l wool. When t h i s had becn dona the system was e s s e n t i a l l y f i c t

up t o 140 c/s.

" " C U ~ ~ A s i m i l a r system has been uscd f o r record~.ng k5o ar,,, i n the mouth. The ovc ra l l Trcqv-~ncy response f o r t h i s eystsL is s l s o

f l a t up t o 140 c /s when using a f i n e r ca the te r (interns?. it<-anetcr >

bout 2 n!) r e s t r i c t e d t o a lcrgkh of 25 cm. This cathc.kor ca;n be

passed round the molars so t h e t its open end i s z t the b ~ c k of the

mouth cavi ty. I n t h i s p o s i t i s n tho pyessurc behind all s=.ticu7_cticr_s

other than v e l a r can bc rocor5od,

Even with both c3-thcters i n pos i t ion subjec-;z c u . 3 ~ 3 ; r L

qui t o na tura l ly ; high q u a l i t y tape-.:-ccordings of nazg ii-t tcra?lccs mcds

i n these circumstances cannot bo 6istbnsished from recor?i?l:;z 01' l h o

subjec t ' s normal speech.

Thc present f crn of oesophagcal prcssuro rcu c rd po-;.i. d c s

a very good measure of thc pressure bciorr tbc vocal cords, I.S.g.. I I I - - I

shows t h a t the mouth pressure and the oesophageal pressure aro v i r t u -

a l l y the same when blowing againe t a r e s i s t ance with increas ing force.

I n these circumstances the mouth pressurc i s exac t ly tho same a s t h e

t rachea l pressure; so Fig. 111-1 a l s o shows t h a t the oesophageal prec-

sure i s only i n s i g n i f i c a n t l y d i f f e r e n t from the t r achea l pressure.

From now on we w i l l say sub-glot ta l prcssure whcn we r e f e r t o e i t h e r

the actual t rachea l pressure o r t o the pressure recorded with the aid

of t h i s kind of ca the te r i n the oesophagus.

A flow-meter of t he type devised by Svend Smith has bccn

used i n conjunction with the pressu.re recording systems. This device,

which has not ye t been f u l l y t e s t e d wi th in t h i s laboratory, employs

a photo-electric method of measuring +he degrcc of opening of a rubber

valve i n a tube connected t o a aouthpiece.

Using t h i s instrumentation wc have conducted the following

s tudies:

1. We have recorded 38 v o ~ ~ e l s spoken with varying degrees of

vocal e f f o r t by one spcaker, and 25 s i m i l a r vowels spoken

by another speaker, The sub-glot ta l pressures , i n t e n s i t i e s Z (rms, r e 0.0002 dy-nes/cn ), and speaker 's es t imates of vo-

c a l e f f o r t a r e l i s t e d f o r each vowel; and the FhI tapc-record-

ings e r e ava i lab le f o ~ fu tu re s tud ics of the voice source

c h a r a c t e r i s t i c s .

2. The r e l a t ionsh ip between sub-glot ta l pressure, r a t e of flow

of a i r through the g l o t t i s , ar,d frequency of v ib ra t ion of

the vocal cords, has been s tudied. A s t he prcssurc end flow

increase the r a t s of v i b r a t i o n of the vocal cords a l s o in-

creases , both because the increased flow produces an incressed

Sernoul l i e f f e c t ( 2 ) so t h a t the vocal cords a r e drawn togcth-

e r more quickly, and because the increased pressure a r e rc-

s u l t s i n t h c i r being blown apar t a f t c r a shor t e r closed phase.

Van den Bcrg ( 2 ) reported an cxpcr im~nt i n which he recorded

the change i n frequency which occurred when a subicct s inging

a n o t e was pushed i n the stomach. Wc attempted t o quant i fy

t h i s e f f o c t by a s imi l a r experiment. The subjec t s a t with

h i s eyes shut , end t r i e d t o maintain a c o n s t ~ n t note whilc

Oesoph. mouth

Fig. 111-1 Simultaneous records of mouth and oesophageal pressure when blowing against a resistance with increasing force. In these circumstances the mouth pressure is the same a s the tracheal pressure.

Fig. III-2 Simultaneous records of fundamental frequency, sub-glottal pressure, and rate of flow when trying to maintain a constant pitch while pressure is applied to the chest.

I

Pressure in cm aq ,

Fig. III-3 The relation between sub-glottal pressure and fundamental frequency in the circumstance shown in Fig. III-2. The points in the lower group indicate the frequency before pressure was applied - the upper points show the frequencies during tQe peaks of sub-glottal pressure.

one of the experimenters pressed against his chest at unpre-

dictable moments. Fig. 111-2 shows part of a record of the

variations in sub-glottal pressure, rate of flow, and funda-

mental frequency which occurred. It may be seen that the

change in fundamental frequency must be due to the sub-glot-

tal changes rather than to a reflex action affecting the ten-

sion of the vocal cords, since in all known human reflexes

the response occurs about 100-200 msec after the stimulus.

The fact that there is - no delay between the fundamental fre-

quency changes and the sub-glottal pressure changes indicates

that there must be a direct link between the two. The results

of a large number of observations are shown graphically in

Fig. 111-3. On this subject a change of sub-glottal pressure

of about 7.5 cm water produces a change in pitch of about half an octave.

3. Data have been obtained on the effects on the sub-glottal

pressures of differences in articulation and state of the

glottis. Fig. 111-4 shows the result of saying a number of

phrases of the form hat' s a mine, hat' s a dyne, hat' s a vine, etc. These phrases were all spoken with the same rhythm and

intonation, so any variations in the sub-glottal pressure may

be attributed to the one feature which did vary, namely, the

consonant at the beginning of the stressed word. It may be

seen that when there is a high rate of flow of air the sub-

glottal pressure tends to drop. This is particularly notice-

able in the (voiced) [n] in the last word. Small drops may

also be seen on the release of the voiceless stops, irrespec-

tive of whether they are aspirated (as in pine) or affricated - (as in chine) . On the other hand, the sub-glottal pressure is not appreciably affected by the increase in the mouth pres-

sure in s voiceless fricative such as [s], which is often a-

bout the same size as that in a stop, does not affect the sub-

glottal pressure.

Many other points concerning the physiological parameters

of speech may be appreciated from a study of the data shown in

Fig. 111-4. Thus it appears that the physiological work done

i n producing thc s t r e s ~ e d s y l l a b l e s may be about the same i n

each case. Thc work done i n tho product8 (sub-glot ta l pres-

su re ) x ( r a t c of flow) x (dura t ion) . It i s not iceable t h a t

the s y l l a b l e s beginning with a voice less consonent i n which

the re i s a comparatively high r a t c of flow a r e shor tc r than

the others .

4. Further da ta have been obtained on the r e l a t i o n between sub-

g l o t t a l pressure and s t r e s s . k s e r i c s of phrases such a s

hat's a torment and H e d idn ' t tormcnt - were spoken with both

a f a l l i n g in tons t ion (2s i n normal s ta tements) and a r i s i n g

in tonat ion ( a s i n qucst ion form). Fig. 111-5 shows the four-

wzy con t ra s t f o r four p a i r s of words. Each of thesc two syl-

l a b l e words has only onc pesk of prcssurc: i n the statements

thcrc i s a c l e a r d i s t i n c t i o n between thc noun form and the

verb form: the former hevc pcaks of sub-glot ta l pressure

during the f i r s t vowel, and thc l a t t e r have pcaks during the

medial consonant or the second vowel. I n the quest ions these

d i s t i n c t i o n s a r e l e s s evident ; but i t i s s t i l l t r u e t h a t t he

peaks of pressure occur e a r l i e r i n the nouns than i n the verbs.

5. A preliminary a t t enp t has been made t o deduce information a-

bout some of the bas ic physiological parameters of speech.

The speech producing process i s of ten considered t o cons i s t - of th ree par t s : an i n i t i a t o r mechanism producing a flow of

a i r ; a g l o t t a l mechanism which may modify the airs t ream; and

a system of a r t i c u l a t o r s which a l s o causes modification. We

have secn how v a r i a t i o n s i n the airf low and i n the sub-glot-

t a l p ressure may a f f e c t t he frequency of v i b r a t i o n of the

vocal cords. hTo may now consider whzt t h e g l o t t e l mechanism

must have becn doing i n order t o produce the changes i n fre-

quency t h a t ac tua l ly occur during thc pronunciation of a

phrase which has c e r t a i n v a r i z t i o n s i n a i r f low and sub-glo t ta l

pressure. Fig. 111-6 shows ( 1 ) a microphone record, ( 2 ) t he

sub-glottal pressure, 53) thc mouth pressure, and ( 4 ) the a i r -

flow during the phrasc: "That's a pervert" . The observed

fundmenta l frequency (dcrivcd from a p i t c h metcr record,

supplemented by inspect ion of the waveform and a narrow band

STATEMENT

Noun - - - Intonation \

Verb - - - - - L --

Noun - Intonation - - C - 1

Verb

Verb

(That's a) [s 3 v e l ]

(That 's a) [p (That's a) [p 3 v 3 t]

Noun

;(He didnlt)[p 3 v 3 Verb -

15

10

5

0 cm

Time 0 0.5 aq

I 1.0

(sec.) , a

( T h a t ' s a) [t 3 rn E n t ]

77- - Fig. III-5 The sub-glottal pressure during the pronunciation of a number of

phrases with both falling and rising intonations.

"That 's a p e r v e r t "

1. Micro.

2. Sub- glottal

pressure

3. Mouth pressure

t s a p 3 v 3

6. Pressure drop

across g lo t t i s

7. "Vocal cord

tension"

Fig. ID-6 Simultaneous records of (1) waveform 2) sub lottal pressure (3) mouth pressure (4) air-flow (5) funhamend frequency, during t h e p a s e qqThatOs a pervertq1. The pressure drop across the voc cords (6) i s derived by subtracting (1) from (2), and a curve (7) corresponding somewhat to vocal cord tension is deduced os described in the text.

Tho simplicity of thc curvc showing vocal cord tonsion

suggcsts that it might bo profitablo to charactorizc spooch

in tcrms of physiological paramotors of this kind, rzthcr

than in terms of ecoustic paramctcrs such es fundamontal fre-

quency.

(1 ) Drapcr, B.H., Lndcfoged, P., 2nd Whittcrigde, D. : "Expiratory Pressures and Airflow During Spcech", Brit.Mcd.Journa1 June 18 (1960) pp. 1837-1843.

( 2 ) van den Bcrg, Jw., Zantcma, J.T., 2nd Doomenbal Jr., P.: "On the Air Rcsistancc and the Bernoulli Effect of the Rumen Larynx", J.Acoust.Soc.Arn. 29 (1960) pp. 626-631. -