BSTJ 10: 4. October 1931: Audible Frequency Ranges of Music, Speech and Noise. (Snow, W.B.)

6.5 MB·English

Audible Frequency Ranges of Music, Speech
and Noise *

snc niece nse slau to deseemntg by ear
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“cae Bees Se he

meted eee tn He tienes

che tecenew ange is

[NY sound cramsnison nyse if i to give faithful reproduction,
AC enouie transmit all the aude Gequencics af a sound in their
Droper relative eration To pee senepicble reproduction. i em
Trarit choce frequencies canned most necesary for czy particuls™
application, The sale Crequcuey range ernends upon physical
Deters the Sreqneney-amplitte craracerilice cf a seund and the
heating cheveterinios of ile avcage eez thersce the acceptabe
frequency rage muse e dacsrmined by jlgmnent when ergineesing
or eciont comsklerations Sit tanamisom. Ae engieering Tmt
sions disippeae sl practical design becomes more a rsater of eo.
omics knnelaige af eta audible and acceptable Hits ixenses
importance

"The progr of Tesi tata deste i thie one was undertaken
trimerly to exablsh the audible Frspessey tamgie of che sounds moet
‘uea encountered in snl seprlution, buc some rete bearing ox
evcptabie soswes ere included. Ike gonimon were teanslted
Trg a elgetun acoustic system cen! with electric! Hiters by
tines hiv equercies above ot below any deze eu-of could
be suporessee, and osoervers determin] the high and low frequency
‘cotit causing just perceptle differences in the lacsnssion. All

Ppa ie Coasen gf te Ae, Sx ety Say 4-5, EN. Pab-
vated ee eS BE
AuDINs FRKQUEHEY RANGES ar

fudible Frequencies of the sounds were Fachaded in the rive Between
the cut-ote thus delineated. Sound sources were: Musical instru
rents, hie era, sare drum, 1" eyabats, fash vil,
Trlle, pom, vin, awe tule, Combone, Keench own, erumper, bast
sasophose, bassoon, bass darinct. elaine, choe, soprans eaxophane.
flute, and pieolo: male and female speech; noises—footsteps, hand
"Sapping, Key ingling. These cote are desvibed in Part

‘Measurements of the relacion of reproduced frequency range to the
suaticy of nchesteal mise, as judged by a number af exgeienced
listeners are reported i Parc TI. Pests this Kv sous wei
establishing acceptabie frequency ranges,

var 1
Apporeiue

‘The reproducing equipment wae ble hy t3¢ Tell Yelephone Tabora

ores eapecay or fumlamencal estes of spec ane mos ante

Fig. 1 ita Block dingeom of the circus involved in thice teeta The

lectro-dynamic misoplione was mounted in e S? square baile placed
near the center of 2 large ecundproot raom, 29° 320" x 13" ia sie,
‘which had a reverberation time ef abou: one second for frequencies
Tetras sand ADM eyrles, The microphone amplifier, moanted at
Ie ver the lll eet she merphove apn ia vel that per
ated raisfactnry swirling open witout objection agen

In anetker room the Alters, sheir switching circ, snd the main
sompliiers were setup, The attenuator shown in the "Aileer-out™ cr
uit ae ued to compensate forthe losses i the transmitted bends of
aus ARLE SYSTEN TACHT¥TCAE JOURNAL

the filters that the sed Fequencoe were epredueed at constant
fevelatall tes. Fiore available were: high yas #0, 40, 88,75, 100
125,250, 375, 500, 78, 000, £500 cycles ent aT Fenceney’ ow pass
‘00, {0.300 4800, 7000, S800, 450, 350, 3280, 2880, 2480, 1900,
1300, 1000 sel 750 cycles cute eequeney- All weve composite struc.
tes giving shorp wells ad atsenutions of £0 dy or moore in the at
fenuated seeion. Represeatative aromuaticn characersti anv ehisrn
ia Fig. 2

“The loud sraker was siouatsd in one corner of a third room, of
dimensions 18° 27" 318, seutksound proof in eosacrucdon sn
(iting revesberation chacaeteiatiessiTar ia those of the micro
Theae room. "To eave the requted frequency ming, to repre acing

unite were employed, nef che four sd one atf-ceeave range below
S30 eye the other forthe fve-oceave rigs above this Freueuey
"The legice of ten'vlence to be placed in the eest resis depends
upon the oviormisy with which this range was reyrmluced. Tae
werage overall reprdetion ratio lacectesistc of the system, shown
in Fig, 3 depart vn uniformity ony about +25 lh between 20 sd
1500 eyelon It repreente the average fr hal pare of the rou
“which ney be called the "Tseng aes," the ection! characteristics
eke lal epeaker not permitting ifort: sound pressure throughout
fhe som a2 very high frequencies, ALto poist sv ths area di the
reamed pessure al sy frequency depart tne than +38 db from
he nverage curve. One sasumpline ie involved, Became the mess.
Iementa were sue by eupplvng “wacbling” frequents to the volt-
AUDIDEE FREQUENCY RANORS a9

nige amplifier and measuring eke souad pressure inthe Hstening room,
inch the regular syatea micvophine aul ample, i ie neceeery 10
assume that the aicrophowe Level identically im the micropione
oom, The two roome ae sinilar and the assumption was thought
Justifed. The power output capacity nf the system we entmated at
tme-half wate peal sourd power with 1D per eet distort prs

"ait to te eh eit, Wig. | shows an fnating lap
SStcuitPlavl before the land spear was a small box bearing the
letter 4 and Bon its translucent fice, As the filters were trai or
ft he annatinn wa ehaged fora one eter to the othe, the eter
trresponding to "flteri' being determined by the reversing witch
‘The signa lights beside the mierophoae wee Tighed whenever the
Srewil eax loa throngh. An exdersviteeicuit (aot shawn) wa
eed Gor signalling ani intereormmuricadon.

|

—— |

,

u Matiots

he “AD Test" mechod was used in determining the Bltercusof

prectcing Gist perocvihie changes in she mms. ‘The observers
listened to twe conditions, sn B. ome ieee al one wafers ned
judged which condition was Steed. che observer obtained a eoore
TOD per ean cereal Large nen of taal he iter
tres sbaulely detectable, A sexe of SM per rent covet judas
Tdisted an undetectable flte, Because the ebeerver, i guess,
iuessed right and wrong an equal mumber of times,

‘Nine members of an rticulation testing crew and two young ene-
neers made up the rating shserving perma, Hath fe aeervers

seere secured iohen pees. The se‘ semeber pirtspating inthe
fests vied from nine @ fourteen. All were lew to have normal
bearing, but the peedaminantly youthful makeup of the eww pohly
sade the crew’savecsge snalivity fr vey high fesquencies some
cater than the geaccal average. The cbservere were Wequeally
Shifted about co ineure average revues, sinew the sun Held was not
absolutely uaiferm.
ea ena, SYSTHAE TSCUAACAL JOURAL

Professional suusiians were emplayed in all ests with musica in-
siruiments, Usually they were wee a close to the microphone as
praelieabl,

sd che ampifers were elon thet the counds were eepro-
ural inndnees. The power capacity ef the eystem di not
ioulress rte drums, eymbale, sian, trumpet) aul
{tombene. For these mie the pevtormers were seated about 10 feet
from the microphone ant the amples gen mae rede the necessiry
Smount. Speaker were sealod with their Lge 1 inches from the
fhisrophone. The hess weve siaken about four fect away. Hand
ping and footsteps were produced ata stan of 18 Tet
‘The mmusiciane were wasucted to play thee instruments loud," 26
listening tests showed anche widest feequency ranges were thereby
produced. ‘Tests were made with the istroments played in ther
everal weave sanges of with thelr dierent techaiques to insure
Tumlary” venulta,In general che performers played repented three
cr fons ane cals, or thee eveaces produced by the boundary flere
tes teo emall zo he detected seguaidy escape or repeated musi rot
ipplied by melodies. However age » rorlore would not be epee:
entatve for the pio. and rerclar player rll vere wei i cestng i
‘One repeated over ant over 215 won passage emshaxzing the notes
cf fundamentals 32 ¢o 800 eyeler.fheseucnd alley emphasized nozee
‘ef frdsentals 200 t9 3800 eyes, wile the third wes a march coves
fg the range 40 to 15UU eye's.

‘Before he regular ex stiri] work ox cach sound the engieersin
sharye ienad to the sepraction apd picked aut ce playing teck
hiques thet promised the idea. Keqieney renges. Test always
Sharted with atte ying 90-100 per cent rorrertjn'gments and cs
Tinued through sustocive cuted anil the SO = peut ena? Wa
Feached, ‘Throwgluaut Boch the preliminary and regular tas3 the ob-
server mae notes restive to quality ceages produced by she fers,
fed nies prtuced by the ins iments. With the performers and
tioverers in readiness fr an seal tat the procedure ws fi
The Ales ogarazor threw (he ws vite from neutal to the postion
ightng the" Alam, whieh night be" blterin” or "lter-out” ashe
ose The performer sting his signa lamp light, then played his
Insteument for a pied of 13 10 20 seco an Use Operator aitched

"TAB entra” Switching to neutral stopped the mascian by
cstinguiching hia signs igh, sl pave the observers an opportunity
heck on heir secording blank the condition they believed to be
“ese. The peocees wos repeated Be times with «random ore of
correspondence betwee Ac Band "flterin.” When necowary
fer was tested una! proces elleets were eliminated. Since there

Bs
‘were never lees than nine obrervere and each al a lesa sx tale on
ack ee, te minimum wane of elves vations used ia computing the
freceencaze of eorrece judgments wt wy Filer va wae $4. Several
ties check teats wese made in which the igh were changed, but 30
filter was inserted, ‘The average seinen os these eats avays were
within the limit SU 4 per eet

“The fice entoffs producing just notioeabe let pon he sounds
sere an sharply dened, Fer every sowed there way betwers Ineent
fff recog every Line and ehe urea never romanized 2 certain
Tecion af apweriahe width where the percentage of correct judgments
decreased from 100 per cent to SU pee cont. If this peeentage is
plotted axainet cutoff equescy a curve euch a8 ie shown in Fig.

ig #_Nanhe of nage eapia agcacey pected neti

results. Curves af chit Kad proved seful for interpolation purposes,
Shut ter wontoars were Fel in he tas depeadent upan the individual
pculsitien of olnervers aud pers to Beat general siznieanee. No
‘lee corelation existed between the impartance any freien range
fad che contours of the curves for the ier uel ly the Blas
{hae wee renngniahle in ew than 8D per cent of the tees were very
finally Ta adition, sense observers canider chat elimination of gk
Trequeaciee improves the reproduction of certain musical sounds by
removing socompaaying nolees, Therefore it vas dsl tha che
seul iafocoation fromthe date could best be preset hy straight
Tacs.

‘The andiie frequency ranges of all lie als tested have beer
plotted in this vay i Tig. 3. "The end pins fn thew ines ave bees,
o Pind Sustie ISCURCAL JOURNAL

Lakeu where the correct judgments amnnted to 60 per cent. Thad
‘don, the fequencite were BU per cent core acgments were obtained
Ihave bsen masked, The region betwen {eB per oe rare ie he
most sigifcant—frequendies alive an below wourd probably not he
Frard at auaitoriuon diane or with othes Tastrumeats paying
‘There were ceroin rowide Liat appavently extended to the higher
nine Fequees a3 judged by dhe ease wich which che highest ltr

13000 cycles cutoft—ws detected. Th these cist the Fines have
been arbitrarily stopped at 15,000 exces
‘With at stewie ras noted that dhe actual ausieal sounds
were anmnmpanied by miler wounds euch as key clicks, ip seis,
“uae” ef reds, and hissing of air. "The cbservers tied to distinguish
between the frequency ranges carrying the wo clases of sounds, ard
cir judgments are summarized by the treatment of the ines of Fi. 5.
indies the frequency ranges thouglat Lo eoavey
of the instruments, amd the short vertical lies

the
rain RNQURNCY was a

define the ranges of noise, Th some cases noise and tone seomed in
eyarally bende

"The saltative observations ae by the ubspsvtes sre se mmaried
fn dhe gots bw, in whic "LF. sea "lowes: fudarental

Tina Voit” Basle npgane Sealy wees parked la ow Law we
PCa ie .

“frre ns

SL. c. very impurtane. Tone goes to very big fon
co Rime cles, Oat es ete ee
ae

"dc Metta ce wore ste Mi cena han Cue cg
ct eta Mn ey" en a ae Toe ee hin

iat bea

oe, ata san

_ shy Ng imgor a legen
Bin ce bt rt nin wae range on ee ge reve on
aw nnd, SYSTEM TRCHNTEAL JouRDAL
Ie is Felt Ut he eae of the playing was suchas co render the com
ments and imeasured frequency ranges generally applicable. These
artes vlnly cepcesene extreme elton er the ober vers wer in
(fet situated unuscally close ta the instrument, they were listening
Ander ineetfaveraive endiions, aad they sd nly to pick out
trliular distortion

“The piano wns the only inrament which li sot require the repro
duction of ite owen! fundanencalsfor erfet file. Thovefoe ens
Inision of 0 cycles the lowes note of the base ick was require,
fd th es fonnd to Be ample forthe percussion ietruments. Tow.
ver, ae the i yer raat marks inde, Hille wan lost when frequencies
beso 6 cycles wee not repreduced

‘Many of the iatrumerts prelneal noises chat extended to ich fre-
‘avences, hat only the oboe, vin, sl nave denn were thought to ex
(hil des toue ranges to she upper andi iit. The setion uf Lowe
fu the ering el tie clatter of ress the reo] instruments produced
ecy prominent salen of his fequesey. Won the is weve wed as
eal te noises were much lee enmizent. Tze rotses indicate for
the ace anal pole ovre produc! hy the impact af eke ci form the
Tips agaist de ersbouchure opering, As a group che lipped instrux
tants produced only maleate gh frequencies: heuer rou all
find mre instramente wraduciag frequencies tering to the upper
he lit, Am upper cuted of TOMO eylee di gov alec: tke tore
Sf most of the inleuibents vo a rrkel exten, BUC cvery instrument
xcept the bass dun and semen ae alfessed by the SDDU cycle eul-
iA drequemey nange of 10) 10 10,000 evees wes shown toe ee
Uialyaatslacecy far speech

‘Becwern tlh AD por cent marke cho bass vil required the grestst
angen? usuives and thw pieola required she smalesL ange

‘Wolves in particular wie chavactorzed by high eequeacies, Harel
apuiag aad ey jingling tere both fol oe vecy denice charge
thy he 13,000 rye fier. ard infra laeung ects ox several ler
ies inate ia high Zrquencies were very prvnives:. Probably
lisa rrizes al contain inant EsequeneiesTelowe 100 cycles and
‘Cansmnim ul de ence anilie ange woud seem etl wore unpor-
fant for oie vepraduetion hae far reprdirsins uf udesl sounds,

ear HL

“The measurements of the qalily changes produced by che fibers
were made uring the came apr bt a diievent testing technique.
"The 18 picce uvetse furnishing te music was made up as follows!
Anpiene rasgyency xAvoas os

4 fest ving, 1 second vilin, 1 ola, 1 allo, trig Tow ute
Tole 2 elariagt, 1 base, 2 French horns, 2 trumpets, crombone,
1 Orumaace The nlayens vere geared in ert avrangement with the
Saline about 8 Trim the eceephone. Tr eigines experienced i
wality judgments wie av observers, Tx (hes tests the iter li
ions nee alas prevented a6 "15" aod he observers ware asked
fae die quality ofthe °F" e>vlton aumesially,conwering che "A
tonite to pesese a qualiy of L0. The ratings coud be eiher Lees
than 10, inliceing degradation, or greater than 1.0, ica ing an iaa-
Triveneat, Condione wee siiebod AB ALR, enbiauiag until
HI observers sad usin a judgenen, bat the ars ware present

| iH wou suas rirens | F

oe

evfectly ulin ier, “Uhersfore de ulacevera ere never informed
pte whar ‘Ther wan ung toate they only ew trac" A” epesenced
auelity of PO aad "Bx eek ta judge

‘The orusira played the Sore wal’, "The Beautiful Blue Dan
be; for Ul fu tees Inwaeeechenrated so that ms of the instru
trons plage ost cf the Hime. All zers excepe 80 on AN high pass
neve eened co taeubververs. Fram the results Hit of lees which
ebscrwers hoe ata beter thom 0.3 seas npited for present ion
Gturing «swine! lest. This time the wore wae “In Tae Vile" =
commits of Gedasd, Fear a session in whch sty iatruments
Fad anfo paste and iv sich thecefore the ehararier of the music
lapel api

“The aveaage ratings for bot rune are plotted ia Fig. 6. ‘The rw
sors nf Aata agree seasonally we except at che exireme ens where