A critical study of the principles and practice of magnetic tape recording

173 Pages·09.034 MB·English

by  Balakrishnan, A. V

A CRITICAL STUDY OF THE PRINCIPLES AND PRACTICE
OF MAGNETIC TAPE RECORDING
A T hesis
Presented to
The F aculty of the Departm ent of Cinema
The U n iv ersity of Southern C alifo rn ia
In P a rtia l F u lfillm en t
of the Requirem ents fo r the Degree
of M aster of A rts
by
A. V. B alakrishnan
June 1950
UMI Number: EP42698
All rights reserved
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U M T
Dissertation: PwMisMng
UMI EP42698
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This thesis, written by
A.V.Balakrishnan rttd 3vT
under the guidance of h~?..... Faculty Committee,
and approved by all its members, has been
presented to and accepted by the Council on
Graduate Study and Research in partial fulfill­
ment of the requirements for the degree of
Master of Arts
Z - ..................
n * .___ M -1950__________
Faculty Committee
Chairman
.........
__
;
TABLE OF CONTENTS
CHAPTER PAGE
X. The problem 1
Statem ent of the problem . 1
Im portance of the study . . . . . . . . 1
D efin itio n s of term s used .................................... 2
M agnetic tape recording system s . . . . 2
Review of the lite ra tu re ......................... 2
O rganization of the re s t of the th e sis . 6
I I . MAGNETISM—A REV IEW ......................................................... 8
B asic phenomena and d e fin itio n s . . . . . 8
M agnetization and h y ste re sis . . . . . . 16
H y steresis ............................... . . . . . . . 20
D e m a g n e tiz a tio n .............................. 24
D em agnetizing methods ' ....................................................28
M agnetic m a te ria ls .................................................... 29
S o ft m agnetic m a t e r i a l s ................................... 30
Hard m agnetic m aterials . . . . . . . . 32
M a g n e to stric tio n ....................................................................33
N ature of m agnetism ....................................................35
I I I . GENERAL CONSIDERATIONS ....................................................40
H isto ry of m agnetic tape recording . . . 40
E sse n tia ls of p resen t day m agnetic
recording . ....................................................................54
A dvantages of m agnetic recording . . . . 55
\
iv
CHAPTER PAGE
Types of m agnetic r e c o r d in g .....................................56
A dvantages of tape over w ire ................................57
P rin c ip a l components of a ty p ic a l m agnetic
tape r e c o r d e r ....................................................................59
IV. THEORY OF MAGNETIC TAPE RECORDING...........................62
Types of m agnetic tape recording and
recording heads . . . . . ............................... 63
The recording process— tra n s fe r
c h a ra c te ristic ......................................................... 69
Recording w ith D-C b i a s ................................................72
The A-C b ias s y s te m .........................................................76
The Toomim and W ildfeuer theory . . . . . 81
The Holmes and C lark t h e o r y .....................................85
G raphical an aly sis ..................... . . . . . . 95
Theory of reproduction .......................................... 98
E rase theory ................................... 108
V. FREQUENCY RESPONSE AND DISTORTION IN
MAGNETIC TAPE RECORDING.............................................112
Frequency response .............................................. 112
D e m a g n e tiz a tio n ............................................................115
P en etratio n e ffe c t . .......................................... 117
S p e e d .............................. 118
B ias am plitude ............................................................119
R ecording head c h a ra c te ris tic s . . . . 121
V
CHAPTER PAGE
Reproducing head c h a ra c te ris tic s . . . 122
D isto rtio n (G e n e ra l)....................................................124
N o i s e ......................................................................................124
M easurement o f d is to rtio n ............................... 129
VI. DESIGN OF MAGNETIC TAPE RECORDERS........................136
Component design ........................................................137
The recording tape ..................................................137
The recording head . . . . . . . . . . 141
The reproducing head ........................................ 145
The erasin g head .............................................147
The d riv e system .........................148
A ccessory e le c tro n ic equipm ent . . . . 149
System d e s i g n ...................................................................150
E q u alizatio n ................................................................... 152
■ V II. SUMMARY AND CONCLUSIONS..................................................156
Summary . ........................................................................156
C o n c lu s io n s ........................................................................158
BIBLIGGRAFHY ............................................................................................159
LIST. OF FIGURES
FIGURE PAGE
1. M agnetization C u r v e .........................................................18
2. H y steresis Curve ............................. ..................................18
3. M inor L o o p s ............................................................................. 23
4. D em agnetization ...................... . . . . . . . . . 23
5. S im p lified Block Diagram ......................................... 61
6. M agnetic Heads ..........................................................................71
7. D-C B ias T ran sfer C h a ra c te ristic . . . . . 71
8 . D-C B ias; D isto rtio n . . . . . . . . . . . 71
9. A-C B ias T ran sfer C h a ra c te ristic ............................80
10. A ction of the A-C B ias on the Toomim and
V Jildfeuer Theory ..........................................................80
11. A ction of th e A-C B ias on the Holmes and
C lark Theory ............................................. 87
12. D eriv atio n of T ran sfer C h a ra c te ristic . . . 87
13. F ield D istrib u tio n About A Recorded Tape . 102
14. Diagram Illu s tra tin g Scanning Loss . . . . 102
15. E ffe c t of Speed on*Frequency Response . . 114
16. D em agnetizing E ffe ct During Recording and
P la y - b a c k ......................... 116
17. E ffe c t of B ias on Frequency Response . . • 120
18. Noise S pectra . 127
19. O utput vs. B ias .........................................127
FIGURE PAGE
20. D isto rtio n As A Function of Output For
V arious B ias C urrents ..........................................132
21. Output v s. B ias a t C onstant Input . . . . . 133
22. A m plifier Frequency Response of M agnetic
Tape R ecorders ................................................... 154
23. O verall Frequency Response of M agnetic
Tape R ecorders ..............................................................155
CHAPTER I
I . THE PROBLEM.
M agnetic Tape Recording Systems of the p resen t day
d eriv e th e ir su p erio r perform ance from developm ents made
during the w ar, although the basic p rin c ip le s of record­
ing sound on ferrom agnetic media have been known fo r mare
than a h a lf-c e n tu ry . These developm ents were th e re s u lt
m ostly of advanced engineering methods evolved under the
d u ress of w ar, and raised the sta tu s of M agnetic Tape
R ecording from re la tiv e o b scu rity to one of pre-em inence
in th e recording fie ld . Combined w ith th e ir in h eren t
advantages, the higher q u a lity obtainable from M agnetic
Tape R ecording Systems has ra p id ly led to th e ir ever
in creasin g adoption.
Statem ent of the problem . I t is the purpose of
th is th e s is to p resen t a c r itic a l study o f the p rin c ip le s
and p ra c tic e of M agnetic Tape Recording System s of the
p resen t day.
Im portance of the stu d y . As a p o te n tia l recording
m ethod, which according to some may ev en tu ally even d isp lace
o th er form s of reco rd in g , the need fo r a study of M agnetic
Tape Recording cannot be m inim ized. Owing, however, to
its rec en t developm ent, no com prehensive study of i t s
th eo ry and p ra c tic e is re a d ily a v aila b le a t the p resen t
tim e. Data on M agnetic Tape Recording are spread over a
re la tiv e ly larg e span of tim e (from 1900 to the p re s e n t),
and are not co -o rd in ated to any d e sira b le e x te n t. The
p resen t study was undertaken in an attem pt to f u l f i l l th a t
need. A system atic a n aly sis of the p rin c ip le s of M agnetic
Tape Recording has been developed, assum ing l i t t l e or no
previous knowledge of the su b ject on th e p a rt of the
rea d er; in a d d itio n , c u rren t design tren d s have been
in d ic ate d .
I I . DBFIKITIOKS CF TERMS USED
M agnetic Tape R ecording System s; By M agnetic Tape
R ecorders is meant a recording system which employs a
ferrom agnetic tape or ribbon, having a w idth g re a te r than
approxim ately te n tim es the th ick n ess. The tape may be
homogeneous or coated.
Only p ro fessio n al equipm ent—where q u a lity is the
prim e c rite rio n and co st is of secondary im portance— is
considered, and a ll statem ents made, u nless otherw ise
sp e c ifie d , are based on th is view point.
I I I . REVIEW OP THE LITERATURE
The e a rlie s t known referen ce to the p o s s ib ility of