An Overview of Psychoacoustics and Auditory Perception

8/18/2019 An Overview of Psychoacoustics and Auditory Perception

1/7

AN

O

VERVIEW

O

F PSYCH

O

AC

O

U

S

TIC

S

AND

AUDIT

O

RY PERCEPTI

O

N

N E L F V IE M EIS TE R

Departmentof Psychology Universityof Minnesota

,

75 EastRiverRoadMinneapolis Minnesota55455

This p

a

per surveys e

x

perime

nt

al

a

nd theoretic

al w

ork on

th

e psycho

l

o

g

y

o

f hear

i

n

g

, p

a

rticul

a

rly

th

ose aspec

t

s

tha

t

a

re, or may be, relevan

t

to audio

r

eproduc

t

io

n

. The

g

enera

l ar

eas considered

include:

(

1

)

auditorY s

en

sitivity

an

d dyn

a

mic

rang

e; (2

) t

emporal

as

pects of hea

ri

n

g;

(3

)

frequency

an

d pitch percep

ti

on;

(4) intens

ity

an

d

l

oudness perception. Curre

nt

work and dir

e

ctio

ns

wil

l be

di

s

c

u

ss

ed

and p

a

rti

c

u

l

ar

a

tt

en

tion wi

ll be d

e

v

o

t

ed

t

o

th

e neur

al

and m

ec

hanic

al

corre

late

s of

th

e

s

e

psychologic

al

ph

en

omen

on

.

INTRODUCTION cessingunderlyingheperceptionof complex,eal

]ifcsounds.

Psycboacoustics,roadlydefined, i

s

the studyof thep

s

y- Thesecondcommentsaboutthemethodsweuseto m ca-

chology of hearing. It is concerned with how organisms re- sure heating, the socalledpsychophysicalmethods. Itis use-

sp

o

nd behavi

or

ally t

o

sound. This in

c

lude

s

resea

r

ch

o

n ba- ful to divide these psy

c

h

o

physicalmethods int

o

tw

o

gene

r

al

sic auditory capabilities, such as the detection and categories: objectivemethods and subjective methods. The

discrimination of pure tones, to more psychological re- distinguishingfeature of an objectivemethod is that the sub-

search on how sound

s

are recognized and interpreted. Al- ject's responsecanbeclassifiedas being eitherright orwrong.

though the term was coined only recently,psychoacoustics For example,we can definea certaintemporalinterval for the

has a very long history and now has many manifestations subject,usinga light,perhaps,and duringthis interval,the so-

one finds research in psychoacoustics being conducted called observation interval,we presenta signalor we do not.

in psychology, physics, engineering, audiology, and physi- The subject is to respond either yes or no to indicate

ology.There are subspecialties of clinical psychoacoustics, whether he or she thought a signal was presented. The re-

animal psychoacoustics, musical psychoacoustics, speech sponse can bescoredas being corrector incorrectbecausewe

psychoacousties, and,of course, the psychoacoustics of au- know whether or not the signal was presented. In contrast,

dio reproduction, with a subjectivetechnique,there is no corrector incorrectre-

Before surveying the basic concepts in this broad area, I sponse, there i sonlya response.In the method of magnitude

would like to make some comments about how we study estimation , for example,the subject is toreporta number to

hearing, specificallyabout our choice of stimuli and about indicate the loudnessof a sound.We are tappinga subjective

the methods we use. In psychoacoustics we often use un- attributeand there is no corrector incorrectresponse.The dis-

natural , simple stimuli such as pure tones and noise. In- tinction between objective and subjective psychophysical

deed, much of the data I will be presenting were obtained methods is importantbecausethere appears to be a consider-

using such stimuli. We have been criticized, particularly by able differencein the intrinsicvalidityof data obtained with

some psychologists, for concentrating on these stimuli, thesemethods.Specifically,the validityof dataobtainedusing

stimuli that seemto have no relationship to real-life sounds, subjective methodsgenerally is far more questionable than

There is some justification to this criticism -- some of us that fromobjective techniques.There has been continuingde-

have become so preoccupied with the psychoacoustics of bate aboutwhetherthe numbersthat the subjectreports in the

simple stimuli thatwe lose track of the general goal of try- magnitude estimationprocedure are pure, true, valid indica-

ing to understand auditory perception. But the criticism lionsof subjectivemagnitude.And this is arehtively straight-

misses a crucial point, namely that we use simple stimuli forward case in the sense that there is general agreement

as tools or probes to tell us how the auditory system about what loudness means.When one gets to less well-de-

works, togive us information about the basic mechanisms fined subjectiveattributes,like quality , the question of va-

of hearing. Few of us are interested in the perception of liditybecomeseven morepressing -- is there a dimensionof

pure tones, but it is clear thatby using pure tones we have quality andcan we validlymeasure it?This is not to say that

learned a lot abouthow the systemwor

k

s and aboutthe pr

o

- the validityo

f

th

e

objectivemethodsis beyondquestion.Sim-

AES8thIN

T

ERNATIONALONFERENCE 13


2/7

VIEMEISTER

I 1 1 1 I

i40 - _._ eardrum to the cochlea, where the hair cell receptors are lo-

12o _ _ rated, and serves essentially as an impedance matching de-

l00 vice. There is a beautiful story of the evolution of the

n-a 8o middle ear but there is not enough time in this talk to do it

o3 j_ justice. The pressure transfer function of the middle ear

m 60 shows a bandpass characteristic that is roughly similar to

40 an inverted audibility curve.

20 The second aspect concerns the effects of hearing loss

When we talk of a hearing loss we are referring to a

....... , ...... ,I , ....... t t change in the audibility curve, specifically an elevation in

z0 100 1000 10000 thresholds above the normal threshold.Hearing loss can be

Frequency (Hz) producedin manyways-- exposureto intensesoundscan

Figure1.Thelowercurveistheaudibilitycurvebasedupon irreversibly damage hair cells, the receptor cells within the

minimumaudiblefield measurements.hiscurveisa eom- cochlea,ascanexposureto certain drugs,ototoxic chugs

positeof datafromCorse[TheExperimentsychoio.qyf High frequenciesaregenerallymoresusceptibleo damag

SensoryBehavior

,Holt,RinehartandWinston,NewYork,p.

and as we age we tend to first lose our sensitivity to high

280,1970]anddatafrom RobinsonandDadson[

Brit

.

J

.

Appl.Phys.7, 166-181,1956].Theuppercurveis thethresh- frequencies.I wouldlike to emphasizehattheregenerall

oldfor painor tickle andisbasedupondatafromWegel is moreto hearinglossthana simplereductionin sensitivi

[Ann.(2)to/. Rhinol. Laryngol.41,740-779, 1932]. ty. In a frequency region of hearing loss thereoften are ad-

ditional changes that can affect perception. Thus, we gen-

ply because we measure a threshold using an objective tech- erally can not restore normal perception by restoring

nique doe

s

not mean that thresholdis a valid measureof the normal sensitivity using a hearing aid or using equalizers

subject's ability to hear. It has been repeatedlydemonstrated or tone controls on a audio reproduction system. The study

that factors that are unrelatedto hearingcan affect thresholds, of the perceptual consequences of hearing loss is a very ac-

Theseincludelearning andattentionaleffectsandresponsebi- five research area of psychoacoustics and audiology.

ases. A fairly recent developm ent in psychophysics has been Finally, I w ould like to rem ark on the incredible absolute

the applica tion of Signal D etection Theory. Am ong other sensitivity of our auditory system . At 3 kI-Iz, where we ar

things this has provided measures of performance that are most sensitive, a sound at threshold produces a displace-

morevalid in the sense that theyare relativelyfreeof contam- ment of the eardrumthat is about 1/100 of the diameter of a

inationbynon-sensory factors, hydrogen molecule One can speculate on why we are so

The point of all this is to be skeptical of the numbers -- sensitive, but I won't. Amore tractable question is what de-

they may not mean what we think they do. We are trying to termines our absolute sensitivity. One possibility is that

measure some aspect of the behavior of a very complex bi- there is a true sensory threshold, a barrier in our auditory

ological system. The strategies to measure behavior are de- system which requires a certain energy to be exceeded. The

ceptively simple. However, with objective psychophysical notion of a true sensory threshold, as opposed to the opera

techniques and great care in subject training, the reliability tionally defined thresholdswe usually talk about suchas for

and validity of psychophysical measurement is close to the audibility curve, is generally held in disrepute. Very

that for physical measurement, weak signals, even those below threshold convey some

information -- they are not filtered out by the operation of

I. ABSOLUTE SENSITIVITY AND THE DYNAMIC a sensorythreshold.(If thereis no threshold,or limit on

RANGE OF HEARING

perception, then the issue of subliminal perception becomes

A. Absolute sensitivity: the audibility curve moot).Anotherpossibleexplanationor ourabsolutesens

Figure 1 shows the familiar audibility curve for human tivity is that thermal agitation of the air molecules near the

hearing together w ith one m easure of the upper intensity eardrum -- Brownian m otion -- provides a noise floor tha

limit of hearing. These curves bound the so-called auditory limits our ability to detect a tone in quiet . This also ap-

area. The audibility curve represents the threshold in dB pears not to be correct, at least for humans. The current

SPL f

o

r a pure t

o

ne presented in quiet as a functi

o

n

o

f fre- c

o

nsensus is that

o

ur sensitivity is limited by n

o

ise, but n

o

t

quency. The curve shown is for young adults with normal Brownian noise at the eardrum. Rather it is the noise that

hearing and the tones are presented via a l

o

udspeaker -- is characteristic of sensory transmission. Transmission of

these are Minimum AudibleField measurementsand

,

un- inf

o

rmation thr

o

ugh

o

ur auditory system is inherently

like headphone measurements

,

reflect, in part

,

the acoustic sto

c

hasti

c

. For example, most auditory nerve fibers are

properties

o

f the

h

ead

,

torso, and external ear. I w

o

u

ld

like spontaneously ac

ti

ve -- they s

h

owresponses in the absence

to call comment on three aspects of the audibility curve, of auditory stimulation.

Internal noise such as this mus

The first is the general U-shaped form of the function, limit sensitivity, not only our absolute sensitivity but also

What accounts for this? There are many factors but the our sensitivity to changes in frequency and amplitude.

most important -- for norm al hearing people -- is the

transfer function of the middle ear. The human middle ear

B. The dynamic

ran

ge

of hearing

consistsof threesmall bones, the ossicles,andtheir sup Theuppercurve in Figure I showsthe threshold for pain


3/7


4/7

VIEMEISTER

frequency changes with changes in location. There is

9o mu

c

h more to the

c

ochlear story but I

c

an just mention in

passing that it is an area of research in hearing that has re

cendy exploded. The explosion was caused primarily by

1o observations that indi

c

ate that we

c

an no longer think of

J the cochlea as a passive mechanical system. There are ac

m so five pro

c

esses that are o

cc

urring and these play a funda

m mental role in cochlear frequency selectivity. An example

e_ of the evidence for active processes are cochlear emis-

30 sions -- sounds that are produced within the cochlea and

that

c

an be

me

asured in th

e e

xte

r

nalea

r

canal

.

1

o

There are man

y psycho

acou

s

tical

m

anif

es

tati

ons of

fre

_ I t t J i II t , , , , ,, ,I

t

quency selectivity. The notion of the critical band ha

o._, o.s z 2 s lO been around since Fletcher's classic work in 1940. The no

FREQUENCY (KHZ) tion rests on the demonstration that when a pure tone is

masked by n

o

ise,

o

nly f

r

equency c

o

mp

o

nents

o

f the n

o

ise

Figure2. Basilarmembrane tuningcur

v

ecor chinchillaob- that are near the frequency of the tone are effective in

tainedusingthe Mossbauerechnique.Theordinatesthe

levelof a tonenecessaryo producea vibrationvelocityof maskingthe tone. A morecurrentconcernin psychoacou

0.1 mm

/

s.DatafromRobles

etal

.[

J

.

Acoust

.

Soc

.

A

m.80, tics is the measurementof the filter characteristicthat un

1364 1374,1986]

de

rlies

the

cri

tical ban

d

an

d

,

mor

e generally, a

u

dit

o

ry

fre

quency

selectivity. An example is a psychophysical

millisecond range, two orders of magnitude shorter? This tuning curve such as shown in Fig. 3. The subject's task i

is a rather basic paradox and is one that has not been adc- to detect a signal whose level and frequency are fixed. W

quately resolved. My own belief is that temporal integra- choose a masker frequency (the abscissa) and fred the leve

lion is not a basic property of hearing, rather it reflects a of the masker that just masks the signal. This level is th

cognitive strategy applicable only in certain circumstances, ordinate of the figure. We see that for masker frequencie

That is, we listen to the world through a relatively small that are close to the signal frequency, a low intensity

temporal window -- about 3 ms long -- and information masker will mask the signal, whereas for remote maske

from the looks is stored in memory. Temporal integra- frequencies a much higher masker level is required. The

don, according to this account, simply reflects an increased interpretation is the subject is listening through a

F

iltercen

n

umbe

r of

l

oo

ks as th

e

sign

a

l durati

on

is increased

,

tered at th

e

signal

f

requen

c

y and th

e

am

ou

nt

of

maske

r re

quired

is determined by how much the filter attenuates th

IlL FREQUENCY AND PITCH PERCEPTION masker.Thingsaren t thatsimple, of course,andthere i

A. Frequency selectivity considerabledebateover whether thesepsychophysic

It

is

we

ll

-kn

o

w

n

tha

t

the a

u

dit

o

ry

s

y

s

te

m

beha

v

es

ro

ug

h

ly

tu

ning

c

urves are a c

o

m

p

l

e

tel

y v

al

id

measure

of f

reque

nc

as a Fourier analyzer -- it decomposes a complex spec- selectivity. I use this example because of the remarkabl

trum into its constituent frequency components. At the similarity of the psychophysical tuning curve and the me

physiological

/

biomechanical level this is referred to as chanical tuning curve shown in the previous figure. Bot

tonotopic organization: different frequencies stimulate dif- areclear indications of auditory frequency selectivity.

ferent places in the auditory system. This organizationbe- Auditory frequency selectivity, in its general sense is

gins at the cochlea and is preserved at the highest levels of fundamental property

o

f hearing and is the most studie

the auditory system. The discovery and delineation of single aspect of hearing. Indeed at one time theories o

ton

o

topicity and the underlying mechanisms is

especially hearing meant theories of cochlearfrequency selectivity.

at the cochlear level

one of science's beautiful stories

complete with a Nobel prize, and truly elegant experimen

-

B. Pitch perception

tal and theoretical work by many scientists. Pitch i

s

a subjective attribute of sound and does not bea

Figure 2 presents data from an experiment that measured any simple relationship with the physical attributes o

the vibration of the basilar membrane --the structure with- sound. Frequency and pitch are not synonymous terms an

in th

e co

chlea up

o

n whi

c

h th

e

hair cell recept

o

r

s

sit. Th

e

we d

o

n

o

t have a phy

s

ical measuring instrument thatmca

figure shows a m

e

chanical tuning curve obtained by mca- sures pitch .

s

u

r

ement

o

f th

e

velocity

o

f a v e

r

y small por

tio

n

o

f th

e

basi- Pitch i

s s

urpri

s

ingly hard t

o ri

g

oro

u

s

lyde

fi

n

e

but i

s

u

s

u

lar membrane. We are looking at one spot on the mem- ally related, somewhat circularly,to music -- it is, roughl

brahe an

d fi

nding th

e SPL of a

t

o

n

e

that

pr

oduces a

fi

xed that att

r

i

bu

te whi

ch

permits

sound

s to be

or

de

r

ed

o

n a

mu

rms velocity of that spot. (The spot vibrates at the same sical scale. The pitch of a sound is usually measured b

frequency as the stimulating tone).The tuning curve shows asking the subject

to

adjust the frequency of a tone (or th

a high degree of frequency selectivity -- only frequencies fundamental frequency of a periodic waveform) such tha

within a narrow range vibrate that spot on the membrane, the pitch of the tone matches the pitch of the test sound

If wc were to look at another spot close by we would find a Assuming that the subject knows what pitch means an


5/7

ANOVERVIEW OF PSYCHOACOUSTICSAND AUDITORY PERCEPTION

bata

b

le a

s

s

um

pti

on

s --

we

can say that the pitc

h o

f the test

.

..

s0

- _ ................

I

s

o

u

n

d

is

equivalent to that

o

f a to

n

e

of

f

r

equen

cy X

. The mt

n

70

s

hor

t

h

an

d, som

ew

h

at

mis

l

ead

in

g, e

xp

r

e

s

si

o

n

is

t

ha

t

the

N,_

p

i

t

c

h i

s

X Hz

. _ 6

0

k ,

There

is

a

ve

ry la

r

g

e li

te

r

atur

e on p

i

tc

h per

c

e

p

ti

on

and I x_ _

can

o

nly highlight

c

e

r

tain a

s

pe

c

t

s

. We ar

e e

xquisitely

se

n

s

i- _

5o

_ -.

five

to

f

r

eque

n

c

y

chang

es

. F

o

r

e

xample, w

e c

an dis

c

ri

m

i

-

_ n

0

nate between a 1

000

Hz ton

e

a 1

00

2 Hz tone: we say that c

e

-

th

e

di

ff

erence thresh

o

ld,

or DL,

is 2 Hz at 1 kHz

.

Th

e D

L _ _

0

increase

s

as the f

r

equen

cy i

n

c

reas

e

s

:

at 8 kHz

, for e

xampl

e

, _ 2

0

the DL is ab

o

ut 7

0

Hz. It is typi

c

ally assumed and it seem

s

10

0

1000 10000

reas

o

nable that these frequen

cy

di

ffer

e

n

ce

s

a

r

e perceived as

Frequency Hz)

pitch

c

hanges, alth

o

ugh,

o

f

co

urs

e

, w

e c

an n

o

t bo sure.

How do we account for our incredible sensitivity to fro Figure3. Psychophysicaltuning curvesfor three signal fre

quencies.The ordinate isthe level of the masker that isnec

quency and pitch changes?This gets us into an area which essaryto just mask the signal. Data from Wightman etal. [In

has

b

e

e

n

hot

ly

d

ebated

i

n

ps

y

c

h

o

a

co

u

s

t

i

c

s

for sever

al

Psychophysics and physiology of hearing

.

Evans, E. F

.

and

de

c

ades

.

The debate is whether pitch is coded peripherally Wilson J. P. ods.). Academic Press, London. 1977].

in te

r

ms

of

the

p

lace

of stim

u

l

a

tion or in

te

rm

s

of

the t

im

-

in

g of n

eu

r

al

r

e

spon

se

s.

It

i

s c

l

ea

r fro

m the

physiolo

g

y

tha

t sho

w

n

th

a

t the 2

00 Hz pi

tc

h doe

s

no

t re

sul

t

fro

m the

g

e

n

e

r

-

both codes ar

e

possi

b

l

e

--

a p

lace

c

od

e b

ased upo

n

to

n

e-

a

ti

o

n

o

f a 200 Hz dist

o

rti

o

n

p

roduct in th

e

peri

p

heral audi

-

to

p

i

c

organizatio

n, a

ti

m

ing

c

ode

b

ased

u

pon

p

hase

l

oc

k

- tory

s

y

s

te

m. V

ariou

s m

odels

h

av

e

been proposed to accou

n

t

ing

. F

urtherm

o

re, there appear

s

to be suffic

i

ent in

fo

rmation for the basi

c ph

enomeno

n

o

f

resid

u

e

p

it

ch

and of th

e

many

at th

e

le

v

e

l

of th

e

a

ud

i

tor

y

n

erv

e

to ac

c

o

un

t for

o

ur

s

mal

l relat

ed

ph

e

nome

non. Thes

e m

od

e

l

s

g

en

eral

ly

pr

o

pose

f

air

l

y

difference thresholds using either of these codes. This is- extensive central processing and can involve cognitive,

su

e, a

ra

the

r fundam

e

ntal one for und

e

rstandin

g he

arin

g, is l

earn

i

n

g-related

f

a

ctors.

The

m

odel

s

ha

ve evo

lved

to

the

s

till n

o

t reso

lv

ed, poi

nt

that

m

an

y c

an accu

r

ately predi

c

t the

p

i

tc

h (o

r pi

tc

h

e

s

)

S

o

m

e o

ther important facts and

o

bservati

o

ns regarding

o

f very c

o

mplex sounds such as bell-strikes.

the pitch

o

f pure tone

s

. A t

o

ne

o

f the a

c

ertain frequen

c

y

can e

li

cit

diff

ere

n

t

pi

tc

h

e

s

i

n

th

e tw

o

ears of a n

ormal-

h

e

ar

- IV. INTENSITY PERCEPTION AND LOUDNESS

ing subjecLThis is called diplacusis and is most easily ex- A. Intensity discrimination.

p

lained

usin

g

p

lace the

or

y -- one

c

an i

m

agi

n

e that

s

light

U

nde

r op

ti

m

al

c

i

rc

u

ms

tances a 1 dB

c

h

a

nge i

n s

o

u

nd

differe

n

ces in the dime

nsi

o

ns

an

d s

tru

c

tu

re

between the two inten

s

ity can be

d

e

t

ected. That i

s

,

w

e

c

an ju

s

t

d

etect a 1 dB

ears cause

s m

aximal stimulation a sl

i

g

h

tly different places, intensity differe

n

ce between t

wo

bursts

o

f s

ou

nd

,

we can

The pitch of a pure tone of a fixed frequency can change detect a 1 dB increment in a continuous sound, and we can

with

c

hange

s

i

n

the le

vel

o

f

th

e

tone

. Th

e

r

e a

ppear

to

be

detect

a 1 dB

bu

mp

in the

spectrum of

a

n spec

t

rall

y

fla

t

l

arge di

ff

e

r

e

n

c

es

bet

w

e

en in

di

viduals in how it chan

ges

,

so

und.

Th

i

s

is t

re

e, ap

pr

oximat

e

ly, over a v

e

ry wi

de

ran

ge

however. For this reason, and many others, it would be un- of sound levels. Thus, for example, we

c

an just dete

c

t the

advi

sa

ble to provide

pitch com

pe

n

sati

on

(anal

ogous to

in

tensity diffe

re

n

ce

be

t

w

ee

n a

2

0 and a

2

1

dB

sound

an

d

loudness

c

om

pe

n

sati

on)

in

audio

eq

uipm

e

nt..,

be

tw

ee

n a 1

2

0

an

d

121

dB sound. The

re

ar

e se

v

e

ra

l

aspe

c

ts

Two aspects of pitch should b

e

distin

g

uish

e

d:

t

on

e

of

th

is

th

at

dese

rve comm

e

nt. Firs

t

of aH,

th

e fact

th

at re

la-

height

an

d chroma. Tone hei

g

ht is

th

at

as

pect whi

c

h in

-

tively s

mal

l

in

tensity differences c

a

n

be

det

ec

ted over such

c

r

e

ases continuously as th

e

fr

e

qu

e

n

c

y of a ton

e

is in

-

a wid

e

ran

ge --

a rang

e

of ov

e

r 100 d

B --

is ano

the

r mani

-

c

reased. Tone height is probably what is refle

c

ted in the festation of the remarkable dynami

c

range of the auditory

m

c

i scal

e

. Chroma is cyclic

al --

two ton

es t

ha

t

are

an

oc

-

system.

Se

condly, it should

be

emphasized that

t

he deci

be

l

ta

ve

apa

r

t ha

ve

th

e

same chr

om

a

.

Th

is

c

a

ptu

r

e

s

th

e

sa

me

- is a relati

ve m

easu

r

e:

a

1 dB

ch

ang

e

at 120 dB

is

a

much

ness

o

f say th

e

n

o

te A regardless

o

f its octave. A related larger absolute intensity chang

e

than a 1 dB change at 20

p

o

int is that the subjectiv

e

octave d

o

es n

o

t c

o

rrespond ex- dB. A 1 dB change cor

r

esponds to a chang

e o

f ab

o

ut 26%.

actly t

o

the phy

s

ical

o

ctav

e

-- the subjective

o

ctav

e

i

s

C

o

nstant relative intensity change

s

a

r

e just dete

c

table. Thi

s

slightly la

r

g

e

r than a 2:1 frequency rati

o

and depend

s o

n fact is kn

o

wn as Weber's Law. Specifically, Weber'

s

Law

the frequency, states that: AI

=

k I, where AI is the absolute intensity

Th

e

r

e

i

s

a

r

ich literatur

e o

n th

e

pe

r

cepti

o

n

o

f pitch

o

f chang

e

that i

s

just-detectabl

e

, and I is th

e

absolut

e

intensity

c

o

mplex s

o

unds. Th

e

m

o

st imp

o

rtant phen

o

men

o

n i

s o

f th

e

ref

er

en

c

e. Weber's

L

aw i

s o

ne

o

f the great laws

o

f

residue pitch , sometimes called the pitch of the missing experimental psychology and dates back to the work of

fundamental, l

o

w pitch,

o

r pe

r

i

o

dicity pitch. This refers t

o

Weber and Fechner in th

e

early 18

00

'

s

. Webe

r

'

s

law h

o

lds,

the

f

act that the

p

itc

h

o

f a

ha

r

monic

c

o

mp

l

e

x is th

e

sam

e

a

s a

t lea

s

t a

pp

r

o

x

im

ately

, for

a wide vari

e

ty o

f au

dit

o

ry

s

tim-

the pitch

o

f its fundamental frequen

c

y

e

ven when there is uli and als

o

h

o

lds f

o

r intensity di

s

c

r

iminati

o

n in m

o

st

o

f

no energy at the frequency of the fundamental. For exam- the other senses. Weber's Law, or a version of it, also holds

pie, the pitch

o

f a

co

mplex

o

f 18

00

, 2

0

00, and 22

00

Hz i

s

f

o

r detecting

s

ignals in n

o

ise: this ve

r

si

o

n states that a c

o

n-

2

00

Hz, the fundamental frequency. It has been

c

learly

s

tant signal-t

o

-n

o

ise rati

o

yield c

o

nstant detectability and is

AES 8th INTERNATIONALCONFERENCE 17


6/7

VIEMEISTER

one reason why we often use this specifi

c

ation. The funda

-

stand how the

s

e changes are processed if we are to under

-

mental question is why does Weber's Law hold? Why are stand auditory perception. Loudness, has little, if anything,

relative intensity changes so important in hearing? What is to do with it. Yes

dynami

c

s are important in music

at least

it about auditory processing that makes relative changes certain types of music but far more important are the spec-

important? We have theories, of

c

ourse, including that the tral shapes of the sounds and their temporal characteristics.

auditory system employs logarithmic compression, but

none has proven completely satisfa

c

tory. V. SUMMARY AND CONCLUSIONS

Finally, I would like to put intensity discrimination in the In psychoacoustics we are concerned with the behavior of a

broader

co

ntext of how

co

mplex

so

un

ds

are proc

es

s

ed

and very

co

mplex sys

t

em and, despi

te th

e stori

es I

'v

e

told you,

ultimately perceived. Intensity discrimination tells us there are many potential pitfalls in trying to measure hearing

something about how

c

hanges in amplitude or intensity and in drawing valid con

c

lusions from our measurements. I

that occur within a

li

mited spe

c

tral region are dete

c

ted and discussed the distinction between obje

c

tive and subje

c

tive

pr

oces

sed.

M

ore gen

e

rally, it has

g

iven us valuable hints psychophysical measurem

e

n

ts

. Th

e

ques

ti

on of v

al

idi

ty

is

about how the spectral characteristics of a sound might be not as

pres

sin

g

with obje

c

tive methods, and the data

c

an be

coded, particularly at the level of the auditory nerve. A re- much more directly related to underlying physiological pro-

c

ent and exciting development in psychoacoustics address-

c

esses. But, there are many aspe

c

ts of per

c

eption, in

c

luding

es the

c

losely related problem of how we dis

c

riminate and those related to the evaluation of audio reproduction devi

c

es,

per

c

eive spe

c

lml shape or spe

c

tral profiles . The impor- that simply are not amenable to obje

c

tive psy

c

hophysi

c

al

tant difference is that in this research the subjects must measurement. We must use subjective methods in some cas-

make a

c

omparison a

c

ross frequency, not just what hap- es, but considerable caution should be exer

c

ised in interpret-

pens within a single frequency region. It seems clear that ing the results of such measurements.

subjects can do this quite well. It is also clear that such ca

-

The dynamic range of hearing is the intensity range be-

pability is crucial for real-world auditory perception, tween absolute threshold and a somewhat arbitrary upper

limit, often taken a

s

the threshold for pain. Absolute

B. Loudness thresholds (measured in quiet) are determined by internal

Loudness is, of course, one of the fundamental attributes of noise, by the transfer function of the acoustic system up to

auditory perception. It is the subjective magnitude of the cochlea, and by many other factors. Hearing loss is de-

sound. It is, like pitch, not a physical property of sound. At fined by an elevation in absolute threshold There generally

the risk of belaboring the obvious: it is almost always in- are perceptual consequences of hearing loss in addition to a

cor

r

e

c

t to say that: the loudness of the sound was 90 dB loss in sensitivity. Thus, simple compensation for the loss

SPL . The 90 dB SPL is a physical measurement and is in sensitivity generally does not restore normal hearing.

only indire

c

tly related to the loudness of the sound. A 90 The dynamic range of hearing is spe

c

ta

c

ular and it is not

dB sound

c

ould be, depending on its spectrum, loud or yet

c

lear how the system maintains su

c

h a large range. This,

quite soft. the so-called dynamic range problem , is fundamental to

I will not attempt a thorough review of loudness but will an understanding of how we hear. In discussing this prob-

mention several highlights. As you are well aware, equal leto, I mentioned that this huge range is available to us al-

loudne

s

s contours have been measured for tones and for most instantly m our ears do not slowly adjust their gain to

narrow bands of noise. These measurements are based operate over a restricted range. Clearly, audio reproduction

upon loudness matches and from these measurements we that does not audibly degrade the signal must somehow pre-

c

an determine the loudness level (in phons) of a sound, serve a large dynamic range. If this is ac

c

omplished by us-

When we say that the loudness level of a sound is 50 phons ing gain-adjustment devices careful attention must be de-

we mean that it is judged equal in loudness to a 1kI-Iz tone voted to the temporal characteristics of those devices.

presented at 50 dB SPL. The growth of loudness with in- The auditory system seems to have been designed to

ten

s

ity has been extensively studied, typically u

s

ing mag- p

ro

cess rapidly changing sounds m sounds whose ampli-

nitude estimation procedures, and we know that for sounds tude and

/

or frequency changes over time. I distinguished

abov

e

threshold a 10 dB increas

e

in lev

e

l wi

ll

produc

e

ap- between two types of temporal resolution: within-channel

proximately a doubling of loudness. Finally, there are sev- and cross-channel. Within-channel resolution reflects sen-

e

ral fairly successful scheme

s

for calculating th

e

loudness sitivity to envelop

e

chang

e

s that occur ov

e

r a relati

v

ely

of complex sounds, small portion of the spectrum, a bandwidth of the order of

I am minimizing a discussion of loudne

ss

becaus

e

in my

2

0% o

f

th

e

center fr

e

quency. Cro

ss

-chann

e

l r

es

olution

opinion loudness is not particularly important in hearing, refers to sensitivity to temporal difference that occur over

While it i

s

a primary auditory attribute, loudness, in itself, widely spaced frequency region

s

.

F

or

b

oth type

s

of resolu-

is not important for auditory communication, speech and tion, the approximate auditory time constants are about 3

music included. It is important if a sound is too loud or too ms. Phase disparities in reproduction equipment may be

soft, but within this vast range we can communicate about audible if they exceed these times.

equally effectively regardless of loudness. What is impor- A fundamental fact about hearing is that the auditory sys-

tant, crucially important

for auditory communicati

o

n are tern is tonotopically organized. At any given level

different

the intensity changes that occur over frequency and over frequencies stimulate difference places. This organization


7/7

ANOVERV

I

EWO

F

PSYCHOAC

O

USTICSNDAU

D

IT

O

R

Y

PER

C

EP

TION

degree

of f

requen

c

y selectivity. T

h

e

r

e are direct psy

ch

oa- I br

i

efly

co

nside

r

ed lou

dn

e

ss

and

i

ntens

it

y percepti

o

n

.

c

o

us

ti

cal

m

anifestation

s

o

f f

reque

n

cy selec

ti

vity -- the n

o

- Wea re quite sensitive to intensity cha

n

ges

o

ver the e

n

tire

tionof critical bands, of psychophysical tuning curves, and dynamic range of hearing. It is

relative

intensity changes

of

a

uditory£fiteringcaptur

e

these. Althou

g

h it is

c

lear that that are important, a

f

act indicated

b

y Weber

'

s Law. This

,

the audit

o

ry

s

ystem perform

s

a type of frequen

c

y-to- place essentially, is also why

s

ignal-to-noise ratio is a per

c

eptual-

analysis

,

it is also

c

lear that timin

g

inform

a

tion is also pre- ly

r

elev

a

nt specifi

c

ati

on

. A

n

important qu

e

sti

on

in psy

-

served. T im ing inform ation, or phase locking, is clearly im - choacoustics is w hy W eber s L aw holds. This is part of the

portant in binaural hearing an

d

also underlies the high

d

e- more general

,

an

d

fun

d

amentally important

,

question of

gree of temporalresol

u

tio

n

of monaural

h

earing

.

Whethe

r

it how

w

e hea

r

and extra

c

t information

fro

m the spectral

plays a basic role in other types of auditory coding, in pit

c

h shape of sounds.

p ercep tio n, fo r e xample, is n ot c le ar.

Pit

c

h is a

ve

ry i

m

portant su

b

jective

a

ttri

bu

te o

f

soun

d,

VI.

SUGGESTED INTRODUCTORY TREATMEN

T

S:

p

a

rticul

ar

lyin mu

sic

alpe

rc

epti

on.

A

Io

n

g

s

tund

i

n

gs

s

u

eis M

oor

e

,

B

.

CJ

.

M

.

1

9

8

9)

A

n

Int

ro

d

u

cti

o

notheP

s

y

cho

l

og

y

how

p

itch is coded at the periphery m this is the

p

lace vs. of

H

earing

,

3rdEdition

,

Academi

c

Press

,

London.

tim e issue I have just m entioned. The m ore general issue is G reen, D .M . (1976). A n Introduction to Hearing, Erl-

how weextract the pitch ofcomplex sounds. It is clear that haumAssociates

,

Hillsdale

,

New Jersey.

the pitch, o r pitches, of such sounds is not sim ply deter- Pickles, J.O . (1988). A n Introduction to the Physiology

mined by the physical characteristics of the sounds -- ex- of Hearing

,

2ndEdition.Academic Press, London.

tensive com putation , perhaps including stored or learned Y ost, W .A . and N ielsen, D .W . (1985). F undam entals of

s

trategies, seems to be involved. Hearin

g,

2

n

dEdition.Holt,Rinehartan

d

Winston

,

Ne

wY

ork

.

AES8I

hINTERNATI

ON

AL

O

NFERENCE 19

An Overview of Psychoacoustics and Auditory Perception

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