BSTJ 30: 4. October 1951: The Reproduction of Magnetically Recorded Signals. (Wallace, R.L., Jr.)

11.2 MB·English

‘The Reproduction of Maguetically Recorded Signals
2B. 1, WALLACB, IR

{its Bald Fal 9185)

aed ie a a eri

Ivenuneerion

"THIN Un at fen yeas hare ae been inorosing we of mays
reciting ia vetows teleptone rseacth appleaiors ovules are
vavioes versions of ee sound epetzozrph sar! im steno eal el
Die’, Soe of tees aes have required a zeonodacing Heal space alighy
ato canszct with the recoring melts. Bernal ume ware ade
Fo dvarmine ti ere of sch spacing and the ralie ware fund to bo
Capris is a anespectedly snole foie, The sence: extn ler

tee geomet Ua the recording problem and t> aceon for
tmeciat the Fig fecu ny hs Uh sansa et ite as okaccont

"This paper discuss celts ofthe experiseneal sty anders fo
fonnparia ste Uioteti calelaione haces on on ‘Sealed sade

Mssvusimyts ar Seaemie Lass

In oder ta messire Sheek of epg Letwucn he duchy bead
unl Che emilan, sr esperene wa set up as inca in Pig be
Teurving line ws sas & 04008 inch Plating of calmer ley
(hv the Ut suse ot bras ise approntntely 18 fmbes Sn amen ie
Flac i

‘This lie oa vse wit considerable care to insane tant the resnling
surace yay teuutly plane ad seooth a peso and Pat trl
Teaonably tue a ite besrings. Speace of 25 arg Th rym seer proc

1, Mathes A. G. Ninian mal. Ha ts “Cate Kay Some Space
ANG te ae auRTME memCAL jouRNAL, SEIDEL LOSE

‘he tng type recon! memes Hal swag, 1 was Tapped ghey
‘a obtain a reseonehy pd with che sxe of the ie

‘A sagledraqueney reovoling as vale with the bend x nmtach. with
the die singe bias nthe nl wy. Then tie open creat reproduced
tipval evel ans mers st widh the esd in cont, al the afer
Ittoducing poper shins al vachas hiskness betoon the epic el
fd the medme, The oe flr spacey nas measured sta parialar
Hequency av revoning spend, Tae signal ve then ers and the proses
‘mas teste for sher needed eeguences rad for sve] eeontepro-
Aue sees Mrasenamvats were eo ade for sses in which the coring
find veomaduciag apeass were fice Cssleab cae was rogue (0
esp Un se ad heel suet ces Una opeeuctble reels cal
Te obtsire.

RES,
afi AM eo soy atop Te ed ae oe
igure 2 shows type! regu ves seasuted at 2 ik/see wea che
teeostcng heal iv eon set -and cr BO04 inc spacing. ‘The erence
botrean ther ovo curves il be elle the spac ee eacesporsing 9
thie ageing wet spre, ram Show fs and noes of he sme sot ici
oood tha, rth exper-rentsl erm, ses era ca very ply ee
leted to sping atd the rcerded ween, by Une nsiialequstion,
Saachg ens = SSCA) dba
‘whetesicng si he sme a il iy bie the repro level
[ecrssel wen s apaing af @ sucess incor hele the rpm
lucy ‘wad end'a nagacic medion on which a iz of ware
ince Las eon
‘The fect chat thie exprstcn Sts the experiential sia mally wall
fn irae jn Fi, where sping las deta messured et umber of df
ferent ps pure na pings ave posted against 8.
AMEMODEEHION oP AAGvEMTEKY HFCORMED sTEVAIS IMF

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Sachs te wattnaine dR

sty ol SN)
148 ome nxt gxsir wemmmeaL ;OURSAT, OCTOBER 1951

nenesrines o au Berar

Tr thi etn it wil be ssl thst equation {1 hol rue al ease
here te spacing elit al a the recorded trark inst ikendy
Iria tins etd oeste nto. this ser, a9 i ers espe
Irestaly ta bey en itis ded sustisng how grease the ele: 9
tren a very eal tecing whet the zeconded vent i small. For
tual, tke the case of» 50 cpa geal rece’ al 4/5. in whic
fae the wavelength ip QUUL iad. partic of dat which eeuested te
{ape fron the repressing lead by enema of at neh would de
Cease the tepoace vel hy 35 eb. A spering of OME Ine would po
luce» quite noticable 33 db lice and even a¢ 000001 inch spacing the
DSS aly os won be maeurable im relly contol experimen

Tn lew ofthe maraltale savotved, i erm rable tat this spacing
Joss may play sgt ole oven in casea whe the zeposong, head
i suppowed to be in entacr wth the medium. For ecm, i has Too
nn for same tine thet chtiering the tape on the reproducing head
fr oes ia the degice 9 entset dus to erie: eretlness a the tape
hn eesult i ampLtude movin of the repre sigan chereby
tive ie “adulation ooee” or “nu bind tye signal.”

‘Wit she ei af equetion {1 if Pesbe 9 estiate the magnitude of
the isis suoviced tone evs-niin. s aatde aboot tre wave fra ofthe
Ioduicon, Take a simle ee, mange tat the roughne of the pe
Mero such set srwehlly module he aera a wer sal acccune
sare abt low “reer. The zeprfoce signal wou kt en be modulated
fie would cori silchand on each side of the conterfrpeey. Te
her fs lhe te sideband con ites Une noduason ais this a9.
Tes ese Ct Chis ze be 10 how a he gna, ther one ean

Calealite the m:sisnnn pemiible excursion of the tepe aay Sor che
Teprarecing hen This cums ext the 1100)" em. orabeut anes of
the wavelength of che re alin Hie! OF cours, the one il wvcength

assume jn hiv example f about short a seen used ara the elect
ecomesles severe asthe wavelength i nereaeed. This i on ofthe re-
fons tht speeds grewior hun 7.5 face, ae vad for highest cualsy

‘One can ao make some eh gualcative inference abuut the elect of
‘he dices ofthe tesording mam on he shape of the rspmnee curve,
AS ean be seen irom esta {L) a2 for Fig 2 wr Traqunsias can be
reproduc wi wey Ete Jes sample spite of ensidenble scing
between che reproducing Fra sul the xadium hie high inosine
sort wavelengths) nay Be appreciably atumaicd by even QODDT inc
saci bate, he heal the selon, Wich ths in mind i is esy zo
sce Chat at high frequen ae x this Lager ofthe mints nearest the
Iepnluing head wil coutsibue é the reproduced ginal. In this cae
(Short ceasing Ue tienes the ein beyond certain amount
an have no eet the prac eel snl eae the eed past
Sf the tapos too Tae Kem the head us make ts eect fle, Consider the
lMlect of Hnceasing Lie thiekness of errata Irom 3 mitt 6 ml
twhea the wavelength fs one on Snew the sgocing low for 03 ml pocing
AUN = Teil 165 db, Wesignal eatebted hy telat ball fe edi
(0.6 mis thick exnpot le fe tha 1.5 lh wee than that sonia by
the upper Ulf ad hence the ine in thickness can do no rote than to
‘se he speeded evel by 1.2

Ate Jower frequency for which x — 100 i how, the seeming
specing ins i only 0.165 dea in Lis ase thet eso the sa ca
fontibute aioe: equals with the seul Ut nblig Oh Uxickness of
‘the medium can nlmost double tae reproduced gal voitaye

‘Qualtacively, chen, one might expect ct iaiesing the ticks of
the senting rein, ater things beg equ, woul ueceave the sexputae
te fa Senses ae eve the higa froqcensycespare reltivaly a!
teced. Thies in cgreemen: it dato >ebled by Kowne:*

The estates of tenis ft given at va eaunae wie caut
bie proves ncapt hy furtner eerie. Te Pas been ply ese,

ievesungey ta thse i wilonnly) region cheighont H
thiseese and “his tay not be the cas, esses pestle, how
ever, to conchae that ats wvelagth af ae Cha yet of he eure
‘wtih Ken doeper than ehout 02 aul rom the suru ram catia
spprectbiy to the rprodeerd signe, Pizthermere a8 the wavelength is
Alene eye this point the tiknee of the fess per of she tape
‘lecreees i inverse orton toh wih the reul has the avaliable da
to daerasen For Lik nan the “ea maps ear cannot conte
Tnint'y tose at ills pe ora nit oes at low frequencies. In fat
thea the eective prt of the tae becores thin encugh ee nvaible dx
Us decrease at 6 db per urtave se jst ened he bl eb por ote
os, givngan “ileal” repent vires whch fa 6k peeves of
‘quencies but which eventually becomes Ha, neither rly nor fling with
father incase in fesuency

‘Spacing los ray contribute im ail anoer way ua the fegusy expe
chanicterse of s mingnetic roording spate a whied tie repeducing
hen mikes conte: with te medio. Ks well Koon to these ho wok
115) ne akLL sumo wormaeerjoemas, oeTOaK 195

Wik mgnetc stuctunes sash as ate gs fn trasformess eae tae Tike
thet intimate wechanieal corset betwen son yrs of a mngeetc cir
tes not ily flivate gsi eter, Ta Tact, even when gent ee 5
taker in iting atch pars tegriier, easuonerts Facey shew an
‘fietve airgap etneen ther athe oPcive with of isa urlly
mounts nae more ths one ra. One eas for this s that the
Derenbilty nf ait mira se a te used ia the cores of transformers
nd pacing aad is vey eric to stain yen the ligt eld orks
fing whi a surface eeive a eng growl Ma is suthicent to mpate very
rious the peat of "shi sate lye
Tn view of thi it tn fw exjerced at the magnetic eontaet between
repmesteing ead sind smelass lee then perlert IF eald working sharing
{he fabction vl Une ad ee doe to abeaten by the raezing mlm
‘Soul! real fn reveal spec betmeen fal and media amounting
Sovas much as re oy Ue elect om froquersy Feponse woul Ie pro
noanced lem. At a seoudigg spot of 7.8, ec. this amount ef wing
Toul cause» bas af FA fy a AI ep, 116 lat 200 ep6 2.9 da
a0 cp 2932 ll a 000 cp, 6
Tess crlain {at faa prpetial eeoeliagsxstem sore Ise of als
ot ues Pepa creer ing io aagnitode of Cie Ie 9°
in other onde Ls anya the elective sping Fr racic case
Ihuweve dict ove Su ar, on inst eager mental rete for its deter
been fesre

‘nina

‘Teoeness Chemamons sex ay Torscaeep Case

Tn he pocting scien a exerienaly determine spacing os foe
tion hasbeen dissusne. Fas soon hata che wewacig hed ove
Say Fun the rearing wuss the zeodest igual level doses
‘This means thatthe meqpetie Hus thrown the heed dceeves IC che dic
leution of wagretination inthe reoingelian were knw it should
be possible fo nape the Bax throgh “he bead and thereby to rive
the posing ss fanctin of taporeta basi, Uniorstely it seems
Slt imple tao thi ents in a exact wy cause very litle
ie known slums tye aghetiaton pater the medi: al becuse te
oometty of the anal ig type Rend makes the Boupdary value problem
fn ewcetingy dieu ane 0 ele

tis pole homers, to obi » stan for an esta ease wich
brat af ose ceaealance to Ure pectic iin and chs sto
willbe present. The rolls sas, of coun, be wewed ith dveskept-
"ao nl they ca be prose expeszentlly o> ele recalcusted om the
Inns af etter Siti ceximpson, Tei hye, however, that iv same
EIRODUCHON OF MAGNEKEALLY keeouMED stats ISL

rucaeure choy tay sete a8 4 gud ta &belier ance ng! the ma
erie eepeodusingpoveen.

‘The prablm wil he reduce to two dimensions by ease an intely
wide and initely long tape of Site thicanese A rocangalr cooednate
Solel he evoeen nich nay te the ental he mide Between,
The nse aed omer sfces of te renga Fes inthe > 9 ple
Isl be cesumed hae toe medium is sinazoially magnetized in such a
‘yt i the mi Ee inet of magneton i even.
»
Bquasons (2) sy thet a vecoding Is pus Hagan. fpr.
tial tac, of cour, Une stance golf her ey hogan roe
‘pusly perpendicuse but rather contsine couiponents of both sorts, Ia
‘Azpendis Lit schon thatthe frequency seponcedoee aot depo the
relative amounts of these two compancats end hence that the canted
results wre equally wid wet the reser ign! i purely engin,
prey serene, ar a-mste of thet

ikopendie IL oxnins encastins forthe ee 9 © rovnd wis sino
«kT yes sng anand fea pla wie These rls hoe

asin ee)

rch deen in allot for, an skew tbe very sila othe
raul for dat mei,

The Toeauteen Revsonveisy Beso

Vigue 4 shows 9 smigrnctel version of the et of Meld rep
ting heal which wi te texte,

Te consis harvest with single ton of exewdingy ine
view aru i. This el yin CoV pe dies bow te
{ace of he recoding mean I the densi of the bar ae made lge
feet, Se amount of uy theeugh ie wll viously ba gatos el
rode Un ian tug any are head wich ses act wth oly
ue ice of the ta apd a> the open reitvesoducn’ vole pet fr
1Sas high a cam bo sotaed with any pesca! Lea

Suppise a very tow gai toxic fn kis ad where the sng
tur oil se and th the msgnets circle completed yng of cone
rite ge shonin Fi 5

Ie the permet o° the hed is very hige nod the gap very anal hen
he the sich ps hg the single tm ei of Fig. UL now pass
ns

Ses sven suceAL. JOM, cerORER 1951

Ahsougl tae ing of Hig 5 ad can Yeomade:9 chee thon ae of ny
Tsne noutd oo the sing. Ts fa thie to, cain based 2 ai
Tr Iype ea re apical ug type ra

i the bar of Fig, + now alowed to become if i length, width
and thsknets. te tas density i cea be empl sl the ux pee unit
wih can be celeated, This ealculation ie ont ne is Appendix Zt the
tape moves the eal ith a veloc 9 I 4 + disetion, the sepr0

way

ced woe ge le proportion to the sate of change of Tx. T he
pend tie i show to be

eos (oi) BD

fe agente
Bee A ssiertt

sve he tate of exange of May uF cv width of he epzecusing

lad meosred in Maal’ po sy

se isthe pereabilty of the repre eed

Fis the lh cro the repro eal and ofthe recorded
stuck in 9 pti ese),
wonwwoenens OF Nanri muita stan «TIRE

‘la Ge selcity ix cafe, ith whieh the seconting iam
uses tho veproducing end.

Jicia the ple value f the inns inteity of ragmetiaion
in the seconing medio meas ngs,

is the thickness of the reatding dius mesred inthe sme

2is the recorded wavelength meisirot in any convenient units,
in th lets acing tatween the rpsodieng sexe nd she
Sface of the reotding mess rvswivnl fr the warwe wn

seis By sizes the crpolad forsouy ie rycen per om

[Note thal saath (3} apples to 9 ting type honed sot) na back gp
she now nae back gp hen vo al the asaable Bux zeae though
tha cng, So of i ll otra to the reine omg the seme ay
ani hence will not cote t Che tepedaced wulage. This does mot
AMlst the see the frequency response carve bat doe contribute &
forstant multipin feter Jess than unity} 9 the right Hand ede of
fqustioa 3). The vale of this factor depron Une eluctannss of Lc gaps
sn! of the magic juni of the reproducing head, Ifthe reuc‘once
the wagantc oases negligible andthe eeluesuce of the Back yap is equ
fo the ructance of the fet gap wien che wolfe lve my
in eto gane the aco wl Le ano-al. ais fcr il ot be sor
Sided fest in chis orate ‘cds ooteule ty the see
I tne sagomas curve hut ely £0 the anise magne of the repoo
fue volt Hold fe interpeeted ae reducing te eetive miner
tr on the reproducing head toa vahi somesrhal ver than Ue actual
smb o

Sescine Tost

“Te Gers e880 ls ow she neprdacell wollge deen og
In cierto compare this competed efcet wich he experenta = ae
fe sia sess too it nese fs hy taaing teant tines tbe
gue 8 Th ge

Spncng Laws ~ SHG (4/0) dss

‘sues vere nde il the expetnentlly determined equation
(in nlc the constants $5 instead the oumpate $1.8. Tae con
puted pecing las onto splat fa Tg.
N15: ae wen, semtos serwstoar.joemeat, ocronue 19S

‘vmeseae Loss
“The effect of the shikneas 97 the recording medium shows pj he
team (120), At lw feosencee Zar which the wavelength i much
cetera the ticknes of the ments educes€328/. Inchis
The poduced wokage fe proportional lo the tienes of tae medium ae
lo True, Thi i the fain x db pur etave character.
[AL igh Hequnces, howevrn, when SS 8 the frm reuse Uo ualiy

io | |
ie | |
9°} manera

a the computed “eal” zene Ba with focuensy and inpondont
(oF the thick of she ti

eke tenn it = 2) freien as

ell

then th pet in pacethess accounts for a ds par octave cheaetris'c
fd the pt in brats vss foe ss ahs 6 5&8 er ove
‘haratvitie, This loss, wed wl be ella Thicess Lee’, ia given by

rc