BSTJ 10: 1. January 1931: Rating the Transmission Performance of Telephone Circuits. (Martin, W.H.)

9.3 MB·English

Rating the Transmission Performance of Telephone
Circuits

“his ager hewn he ting of Pp ranean
sain etn he nea Sifts lone
‘Taspned in te Bel Sytens For ureroaniog sn expe the saa for
SEE DW eta sine al

METHOD of ring the tsisasikas performance of telaphine
EN eireuits sof eourse an essential inspecting the grades of trans
Inision secvice to be furnished, in desiening, constricting and matin
fining telephone svetems to provide the desind grades of service
‘conomially and inthe eveepavent a he arog elements of the
telephoe ster ayhich afer fin trams Ax the art of tee
phone tranemiscion has developed and greater refinements seve Secome
possible and cesveble, enanges uve aacurally been made ix the
Inethods of specifving and rating transmission performance. Since
‘many euch changes have heen made in recent eats it seems coporeene
ta disne the sving nf transis pertormanen ind so set forth “he
Facing tnetheal whi i roy Ising scope? She Bell Syste foe
determining sel exe Cae Dats for Uke uasetaton design of che
plant. Un this conaetioe, vacous aietiade which have been ent
lave focmeasuring the traasnssen performsat o telephone icles
‘vl be discussed 9 indiente thes app ieaPon ane alza thie relation ¢0
the sew rating metsod, Tt is the pipe mene to discus thie rang
‘matter pisnariy trom the qualitative standpoint rather than to present
Jin quauttetive deri the vnioge relations imvnlvod in rating elepione
transmission, Obi, evdelenniation of many ofthese relations

Drewsts slient iintsil Soc separate tease
Tin extrying on a tlepreme cums thnve joe fanetonings are
involved, namely, that of the talkers formating his We al gto
ing words to convey these ideas, that of the tepiione circuit in taking
the sounds ofthese weds renin Lena ater peat, and
Tasty, thar of the ietener in bring ed rege these reproduced
ounce and in compresenting the ‘leas whieh They are intended to
feomvey- Thor evidans that all huge of there functonizae afece the
tcnw uf the Leplione coaversatien. Sizes, however, che function
ing ofthe tale ad stner are commen ta buch iret eeahone
ions it might eve tha thems of he tsa
peeformanceot telepzone rest could be limited toe funetioning of
{he elute tell. Un Ene with the, cere has been some cea
Fonne uch considesations to eleions between the sounds repro
by the telephone eieuit avd the sounds impressed upon its ‘The per
fenmangesof the talker aad listener, hewever, are materially afceted in
‘evan important respecte by th telephone eat, and determinations
of the celstive merits of the trnsmwion performances uf vllferent

rlehove cvete sunt therefore 9 folher than the perforsiances of
the cteultsthemwelves and take aout ofthe eneainad atin of the
talker circus and Beton.

Caangcrenisrics 0” Cowwansetion
1n view of this reaction of the telephone ceca on the taller and

listener, attention is directed tn the pertinent characteristics of thee

revformances ir, ls fae-tn face and telephone crmvecsatios.

iret Conereation

In inet or face-to-face convevaitions bot the talkse and Hseenee
more i ess subconsciously adjust their aetions in many respects to
faeh other and tw lieie cumstances. The loudness of talking is
plate! intially at a level whi experienve hae showa to be suitable for
Zhe eondiane ard forthe pariulacHetenée. If the listener inicaes
Teubaly or by hie exproson ie he ie wlerstaning casily er with
italy, sue Further adjosimenc aay be rade i the loudness
falling. "Since the taller jadges his owe talking level aggely by the
Ioudecs wish whi hears son woe, Us eve wf felon
Of the asowae of reverberation in the place in which leis talking
‘Avpaveniy for a wile variation of isles in the customary talking,
Tange, the speaker it in general vorsinse of ee arsoun of energy
tnhich ec expending. Noige at the nace ef conversation alo plays a
Tht ia ceterminig he talking loves n fe makes Wyde> ealkng
esesoary in onder pena given deg-renf understanding onthe pat
oF the listener,

Along wits an alustment in tking level, the tlleer may improve
his emunciaciow fdiculry of waderstanding i expected vr indicat
I te listeaesr here may also be a cane in the manner of rx
ig te ideasin snag words which experience has shen are siicus
toudeys als: ea may be ett! nove than ane way in oede>
tw insure its comprehension, Diles adjustments un Tie pat oF the
talker may be determined by his opinion of the mental sity of the
listenes, ly the faaity ofthe listener wit the matinr unde di
‘cussion and by the interest init. These factors affect the way of ex
arersing on idea. che Kin sel number of worde use ati hence the
‘me taker,

‘The Fscener also adjusts Kimelf to the conditions ya amount

ft js determined somewhat. hy his interest in the aiatter under

Giscussion. He may strive lv comprehend the travsmit{ed fleas and
require few sepettiona by the peer or he miei from exerting
Vinal and so ‘tend to evoke greate=elfort on the part a the talker.
Ac times he ay pretend not wn usderstane iz order to gee coir
ff 2 statement oto gin tna in replying to 9 mwestion.

dn view of these factors and af the normal variations of diferent
callers snd listeners in all these ceapects the portion of the questions
and stalemens of emversation whichis corretly understood ana the
‘ime required ta interchange certaia leas nay vary widely for diferen,
conversions even wea they sie cari cn under a End se of al
ronditons, If it weve desis! usietermine a meneure of fe conversa
tional satisfacoriness these mins, in adtion to some yuaniea
tive mete for rating each eoeverstion, thete well le required
thereove,alservations on a large tuinbes af nonvereations becween
dliferent people in onler to take arnount of the variables due to the
material of conversation, the peopl, and theie abilities and desves co
{accommodate themselves to ce conditions

Tepicos Comsrations

Th telephone eorveretions, here are adjuscinents teen talker
ani listener asthe cas in dees conversations, but there ae certo
Aelinite diferences inthis sepsed hers of the iaterpositin of the
telephone circuit between the participants. Tere also, the speake:
tends adja Is lalkng level to thelouines wih wea he hears hie
fown woiee. In this cise, however, he hem bs ew voice nat ony
tieeugh the air pach, but abo throigh the "edatore’ of the telephowe
set, that, ehrough the electra path érom his own tomaaitoe to his
‘own receiver. When this electrical path is mire eficient than the
acoustic alt, the eidetone will tend f9 control the talking level. Le
ls hee ound that varying the sdelone of the ae has on the average
8 defnite effect on the talkizg volume of the epsaker, the talking
volume being lowered as the effiiaacy af the slovne path besones
eater

In a telephone conversation, theve ie cvw a vedeney for a peison
in talking tondjuse is volume on the basi the levalnes with which
hhe hears the person at the ather end ofthe cvcut. I the voice of the
other perscn comes through weakly, he judges that the connection re-
duit lout alking and acts acconlingly. Ifthe listener inlets that
RATING TRANSMISGION PrRrORIEANCE w

We i uot undesseanding, de taker may tall mone nly cose to
is eeanstter alia ae such etrimete entation ad in
seiting forth hs Mes. in the case of direct conversation. Aso, the
Teuduces of tolling reay be sceted hy the room noise st the loeztion
fof the apesler, wie nose inidencally may nol rea este and
sor play no pact in his een, Aside trom cases where the ream
Teise a the fas end je severe enough to be heard over the teepone
"Sree, the speaker dose not ave elt knowledge of the room woe
Ie the listener's end ae therefore ie uot ia a position to adjust hit
Iman of talking to this condition exert in =o far we ester my
Sndienteiietuy a uaderstanding

Tn Ttening che venue ia of eaare dependent upon the position
the recviver with respect t the err, The lral ranma nose reaches the
arto whic: Horreiever laid ath by ee path betieen the ee 2p of
the recive ead the ear and a throng the sietone path of his te
howe set Some telephone ase have learned thst this fest may le
Feduced by holding the rmviverUghtly to the ear and by coved the
tnouthpiece ofthe transmiter whan they aze stoning

Tet evicent. thatthe success ef eeparme convents depends not
on'y npn he pétfinrmanee ofthe teleabone bt pon the pestorm.
ances ofits rer, he matecal of their conversations, the way in which
‘hey talk into Ine tessamniters and hol he reosivers wo their eas 2nd
the room zuisecin ens. In ation. fesseen Ua Tie peoomance
tthe telephone fete pecinenanees of ee uses in such imporcant
Tespectss the loins ealkng, the menner of preening the ideas
fd che amsunt uf ells exerted sa uneerstarl, Ay the eect a the
‘out noise ia function of the crsue sharers, Further,
the reactions of the czeult gesformance om thew of Use sara ate aot
feonetat Tat “ay vary om oeveon to pera sl from cuuversatins to
Conversation. Is vw of she curd nadure nf Che factors, whien
re bejund th satu of those whe design arid pera the telephone
[Suter tre serve perfomance rating oft seephione eel. should be
tn a basis which takes adequate aero other sanges ead combina-
ionsin rarice, "This pois to rating based a tacistical analysis
Uf eealts obiained under cervicesmuitons

Ts determne aa ify thes factors o that it may be ee: hae
todaplate the ange a sesvice conditions in hileratory investigations
troul bea praigiossrazk- Maronee, the duplication of these ond
Tones coutol i bound softest lage lament of artical
whieh woudl viiate the results or et least re nerings questions as 0
their depend

“The yacteal solution isto ge: ancient cae regneing the vesuts
‘obtained over telephode creultsofdiferm perionnancecharactsistics
ms Bes sisrase racusiean souRnae

by their necmal arene a esrrying on reine oomvenations. Vhs re
ifviees a soilable qiamltative mehed of rating conversions ard
Sheervations en a siicient rimber of conventions over each cseuit
‘condition tah ovestgnted fn constitute a reliable sample. Tis docs
‘rot mean reeresrly that all ihe practeable cireit dition have £0
bie observed in this manner but rather that saficent data be eo ob-
tried forthe establisiment of enrelaions with performance meaeuse
tmenisorhich sre siscen be to lalrelary desertion, Tae fda
tena pin that merce performer ling net tbe Ie
sevice results in onder to take proper account of all the factors i
solved,

‘Teassnssion Punvonsiance oF Cuncuuts

“The csinetion has Leen stade betwee tn Kinds of tievanison
peslornance n'a lepine circ, nauely, Use ialcated by relation
berween eutput and inpit sounds and thet indicted oy the results ob-
‘alned Sy te uses of he telephone in ezzrying or thel= conversations
lundsr sevice conditions. Petformance indications of the frat kind
willbe referred tons “transmission characters” ofthe eiteui The
coord kind ef performance my be tered "ramos eervoe pre
formance.” The distinction betreen these tv Inde of performance

portant ne snd shoul ye ep leary nie
“The cnet roars cdeal with in transom chararteriies are not
only the reprviuced sounds which corremond to the input sounds but
als te acconnyingextraneints nes whieh ave daliveed Iy the
resi. kn, the enna stumds to Tie Fnveligated caver at only
those deiverat by the receiver at the far end of the eicuit Buc
hove vepreducel by Use smiver iy Une sation set containing the
tuarsnites england ly the ut souls. Te sous om the none
ceiver include both thooe tansnicted Chugh the sidetene pach of
theset and dose eturvl to teseading ent by selection a impedance
‘cegulasities nthe cieuit Duet the Lave coqured fee propagation
over th cveult these latter sovads may be delayed wish respec to the
fldetone and hence appear as echoes. Likewise, echo sounds may be
fleliseced at che far tecevess

ranamision characteristics do not in themacvos show the service
performance as realized by the usersf the elephone but are essentially
indications of the fusctioning of the ccuie in repratucing sounds.
They prov, therefon, mins for freetigalg ml sige
performance of a teeihone circu without involving my, ad cre
Iknd of tranemission characteristics any, of the actin of the taker
fad the listener fx convention. With the slaflstnent of proper
oveelatons below Lasamision eercce perfurmaroe an sane
Sinn characters. hess Iageer can of curse be wed to iadicate
“eivice pevformance

Ty eto ln specfying any ‘nl oryeede ot eieult peefrmence on
the hass of performance sesute there the metiod, which has had
iemsorlant practic! application, of Siting performance in cerms of
type of insisuments owl creuics ed af che conditions of their une
Nor evampih, a statestene of ie types of transmitters, recive
Station set el con eitcuits and of he lenge and types of loops and
ronks together ith speilc enadiceas of uee, provides a7 indirect
sciication oF a prefiemance. This methed. which is ecensively
Tred in many Gelde, may be termed the "instrumentality designation
meth." Aw outstanding sy"eation of tis metiod in telephone
ansvishrr worl in the Standard Calle Rececence System which
was so widely employed to provide a scale of pesformance. This
Inethee! hee suny”preseat applications where pyc determined
htaccess ave vovaabls or ae diffu of definite detersintion
Sand specication. Ako, the designation of nuieumentaiten ix om
‘erent in way anes because pravi x cely mean of specifying
{borseei enainatio of varios Kad of Uanauision racic tis
‘While this method ie vihan expadiane practically, taken byte, is
inherently cumbersime for the dovelopment of improved instrumental-
ties hecnuee ef the lade of paiealfadcation of the Features to be
investigated,

“Fronumiosion Chores

“The neler Ui listener ef the speech sounds repreducel ver a
teleohone circuit is a faneti of User loudness, of tee distortion ox
Cegiee of departure from lasiuile reproduction, and the suagnitude
find character of the ext-wisous sous 0° nose whies aerompany
fhem. Trsneaisinn charaeersties are thereonedtirete yearly
indiationse the ellecs ofthe ciscut and ies rts on Oe repro
tr sounds in thew (ace respects Ae ares indiated, tancsisice
hates ave Gesermins ot omy for she pat from teense
Stone en bv seeciver at the ather, in abo for the sen ant ache

‘Speech ectnd fs vamision chacacusstics, thats, express of the
relations bev tee prea ead sepreduced epoech tound, while they
Iinve been extensively sed, present sire silfelty fr quantitative
Gecrminatins and specication bmsime of vie complies alae
‘Als, she Invwan clement ie involve in the persons sed = generators
stn spmet soul he investigate aml ax alservers to give indica
ono Fouls aod distnetion wed of thee ete the recite a
the reproduced sounds. Two autstanding Kinde ef ations of this
type are tose given lay volume txts and articulation tess wich ill
he diteuscd lates. Ic haa therelore een of great enavenionee tale
further step and to study and epsciy the performance of telephone
‘leeaitsand tie pastas tavans of Pier furceonng for snglegueney
ound and cutient. In this procera, this fusetioning 4 inveat

gated for a numberof deren cingle-trequoney sounds and eursents,

fo takeo asta cover the range of frequencies eansmized by th ize.

Tn the sinsleSrequency trancmiscion characteristic, the pessoal
lement je elimina snd the measurements are made entirely 0a a
physical Basis

‘A great desi of attention hat boca given wo the errlation a eee
anind an single-freqnensy tnaminton aracteraces sn to embe
he farmer te derived Iron Uve latter and s0 exten ewer
ofthe type whichis mare ealily suseea ie iy qua alive determing:
toa,” Alto, use ae besa made of eally speciiahle sult Grequency
sounds and cusicnts % permit the physical measuressent ca appseael
‘ore nsarly speech znd conditions of phonagrapuis-aprodustion te
rede the pers ctor in the generation of speech sounds for mei
urement purposes and of meter arrangements (o simulate the ear rat-
sg sn parties rly from the staan of relative lone.

Ms result the orectackm spect nul single Frequency charac
taiities, extensive use les buen tale of determinations at selected
‘ypnal single frequencies to check the desiga, inatllaion and main
tenance of linea and other aseociated ciseut elie,

‘The widely used volume ter ie eesotillya scans of specifying the
action of a teleptone creas er ite pare, on the relation becweea the
reproduced and imoressed sounds fom the staxdpeiae af tir zlaive
Totdness. In this text use has been made for many veare of the
Stanilarcl Cable Reeve System nul renal a the Mosler Referee
System for Telejione Tratsenieian * relerenwee for nomi
“These eferenc circuits with their sdustaletrums provide a means
of obtaining different loudness catioe Between input and output
sounds. Hy talking alternately over the seleveace ieuit and the
fone bing investgaced and adjusting the trunk of the selene
‘ntem until the output eounde of the owo cscs ase judged to be
‘sqully loud, a specication of the leudness reproduction ratio is
"blaine! of the eit arler fmvestigition im temms of th engl
the trunk fy the reference nyse, "The effec of a chimge in the
ecephoneciretit, euch as the wolacement of one receiver by ancther,
is meme! in terms of the ehasge required in she referece wan
fo Eve st Tounces balance for the seremd eondiion. In this way,
Sennuremencs are alo ebtained of the elect on the leudmes: rere
Tnetion ratio of the vious pats of felephoae cxcuits, When the
UGreuite ueee commercially consisted of angaracus and lines sins Tae to
therein the Seandrd Cable Reference Syatea azd che major r=
rolls fecter sae the lenbnessrepreduction ato, wc measurements
Constiutal reasoaably segue means for indieting the comparative
functioning of eget aad apparacus

"The noize oa a telsiumeeiteuit may be messaced in various ways
“The method which ae boon most genezlly used i that nf eonpating
iesith the contollable cept Fac source ofa complex wave shape
fod adjusting thisouept uti en the ine noice are judged e9heve
‘ual interfering elle

‘With the eval ity of cscs el appavetus Roving wily lifer
cent ilstution eects the volunze cetings berame inswtilen: [or inl=
Cling the relative perforanies of commercial cuits, The eariat
fethed sed in ral llscorion eels we oae in which obververs
Tetenine to transndavion over the cvs, gave judgment as o their
celative meri By 20 ermparing various kinds slants of dist
fiom two at atime, relsive ratings can be eva for placing them
Sinner of susie, Phieyronedose was partralaly seh Ve eal
tlayein woskingeut the designacttraneitiers ad receivers, eerily
from the scandpoin: of the ination in she Fequency sea of their
Prines of maxim response, Whig suck 4 judgment metal has the
lorteoming of nat providing quantitative radags it hax Ime found
hat experience elnarvers cant in general obtain resles which are
Fdativey cimesient withthe reaulea ot mone wefite measuring
methods, Such judyrent comparzens of slitnrtion eects ane fr
{uendy ured pF ia exploratory work, and are sil se or [ess
‘oceouily refed per. in sting liv iadiens on er ayers which
primarily alles the aaturaess of reyueduccien,

‘To provide forthe nse of a mela Lor measuring the ration be
trscen the reproduced and. mesa sounds from the standpoint i
ects dilevent kinds of distortion, use bas been mv of te artic
jen testing snethoc? In this mela, hich has been widely in
recent year lists of syllabi, usally mesninplens 1soaasyV ables. re
Called over the cinco be ceded sd Fie percentage of syllables cor-
Fectly underside taken a4 8 mmasuee of the cieevt. pesformanee

‘Aneaton Tete Mei Fs: al Stirs, Bi ic. Jeary,
‘This tecting method thus offers a means of indicating the distortion
cfccts of cixeuts in terms of the recegnizabilty af Ue repralanel
founds of speech, Protubly one of its tnt applications * was ia
Gecermining the cutof frequency to be used in the design of coil
Toate eveuits

“The aiticuacin testing method provides, of course, quantitative
rmosauve ia cess of che tecognizalility of the repmatieed nce of
‘avec 40 oly of station elec et elgn of Une effects ofthe low
‘hes of thage founds and of the noise whish may accompany them
‘This methed has provided a vecy powerful tool for inveatigaling Ue
fleets of changes in the reprecuction charectvaticn of telephone
‘Seeuts on the reeognsion of the mprecaced sounds and has been pe
ticularly useful in inicating the lines to be followed in reducing cases
of distortion ip clreuits and apparatue and ia evslusting che impair
feet uns yoo feline crits. TH has been otogriaed,
hhowrver that whstenich metarrments cae the capabilities of the
‘iret n eoroluing cognizable speech sounds they do natin then
elves give veel mensueés uf the depree af sucess which the users of
the tlre chtain fn conventions where thee acta are fee from
fhe conte! which ie necessary in articulation testiag and where the
ccetestural elation of che words plays such a large pat i their recog
dition, ‘Te make the results of thls type of cesting approach mire
early the converectiovalreeulte, words ard ecrtencee have bean Used
in plece of the meaninsless evlables bus i is evieae thet even wich
featencss the contol on the actions af the sesters and onthe ideas to be
ommunraced presents cone in which i ite iene rum those
of regular conversions

All these wave of investigating avd measuring the yerformance of
telehone irate 4 reproducing seuss have sea peti fn

Preset ray trannies work.” Frequently Iki chmvenient £0 use
Aiferent amills ir ‘Le varhius pure of accel iv peclying the
‘complete ‘unctionig of the cece in eeproduciag coun.

‘ranamisaion Seeice Performance

Prom the standpoint of the ures ef the telephone circuit, the trans-
rnission periormance is mess! hy te sucams whic they have in
casrying on conversations over thesdray. Diferen degre of mene
fn thie proce may be taleen ss Ieing indicat by the aurmber of
failures fencers he as arated over the eine ax Dy
the swt af flor. rogue cw the fat of the weer te Hepa atl
receive thew lost. Service performance is of courve allen leo by
ey." Capel Pal Mop, Im 9,
sevdenal ireyulaitee rel cuditious wach ae ierruptions and
futols, but from the standpolns of sransmision deiga,etrecton can
Se coacentrated on the ressles obained witen che cireit isin nora
soe-ating condition. Sinen fihiver to undeecana al exerton of
fort gre experiences a lies verti, th cease fa
telephone conversstioas obviously cannot De extire'y ascribed to the
Suustioing of the ciceut, Variavioas in thee facta for diferent
typeset cueuits cap, however, be used as. measure ol che cect of the
slifecenea sn te transniseion caetreteristis of these cette

Tre sngct tone rere fn ones tnn ear he nosed ta desea
wivsttinof heer fasioepretsciiclin There edly
Th uedey i ering on Comesaiony a nei acti,
‘sect nn moe efore chan is necessary to chtain was the particinanee
consider 1) be sutsaetary results. Tals offer, however, IL ia
eneral le iver av Ce ilietey_ conversing hearer
‘ul bears «teation ta the ierease in reeiFans. Alo, 3 prob
Sle tht Fale vive whic aie the nme rll eis
tons when toed for thesarve sevice, will, on the averse, Far the
same isniwat ef afar by Uhele oer.

Th Line with lca, the cate of oeauvecce of sepeitionssequceted by
tne users ofa paricular teloptone eieut ix cen-ying om eis regular
rls of he ceo. Ry ering he rei rate fr
Ieege enough numberaf diferent yevale at che two ends to axe accoust
ft the sry of thei penal enaracterates in sig site
Ing Ur the telephony tse cumvneidonel material av nalts
{Teting ean be pleced ot the serve aorded, ay making tue obser.

tions cz connections having diferer: warszision characteristics
relative Tasings canbe extablisod fer these various eronsrision
‘Shania

TE soul be sangsiend, Ieves that web dhe sate ob aspects
requied cau oe uve Gus welive vatinge of the Usasuseion sevice
perlormsace of diferent cicuits such casings in themesives da nt give
complete picture of tie sevice lana che uses staadpoin: because
they do noc how dieetly Cae aunout of eHove seguives, Sore ea
Hel neerte can be formed by the observers wh are rata the
requis there he gsc itanive. Ryan ts re rep
‘Yon fate ard ello: there is ubloubvelly aaother faetoe wie sete
Urewser# opis of shesecviee. In ennversing aver ackeuis bovine
poor sranemisson penimance,annoyanee ot initat.on my be fle by
"nests because ebe amount: of eer required may be eosin!
"won tw Le uaeessoaahle, These factors, by their smallness or large