MANUAL OF ANALOGUE SOUND RESTORATION ... - British Library

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Analogue Sound Restoration Techniques MANUAL OF ANALOGUE SOUND RESTORATION TECHNIQUES by Peter Copeland This manual is dedicated to the memory of Patrick Saul who founded the British Institute of Recorded Sound, * and was its director from 1953 to 1978, thereby setting the scene which made this manual possible. Published September 2008 by The British Library 96 Euston Road, London NW1 2DB Copyright 2008, The British Library Board www.bl.uk * renamed the British Library Sound Archive in 1983. ii
CONTENTS iii Analogue Sound Restoration Techniques Preface ................................................................................................................................................................1 Acknowledgements .............................................................................................................................................2 1 Introduction ..............................................................................................................................................3 1.1 The organisation of this manual ...........................................................................................................3 1.2 The target audience for this manual .....................................................................................................4 1.3 The original sound................................................................................................................................6 1.4 Operational principles ..........................................................................................................................8 1.5 A quadruple conservation strategy .....................................................................................................10 1.6 How to achieve objectivity .................................................................................................................11 1.7 The necessity for documentation........................................................................................................12 2 The overall copying strategy....................................................................................................................13 2.1 The problem to be solved...................................................................................................................13 2.2 General issues.....................................................................................................................................13 2.3 The principle of the “Power-Bandwidth Product” ..............................................................................14 2.4 Restricting the bandwidth ..................................................................................................................16 2.5 Deciding priorities...............................................................................................................................17 2.6 Getting the best original power-bandwidth product...........................................................................17 2.7 Archive, objective, and service copies.................................................................................................19 2.8 “Partially objective” copies.................................................................................................................20 2.9 Documentation strategy.....................................................................................................................20 2.10 Absolute phase..............................................................................................................................22 2.11 Relative phase ...............................................................................................................................23 2.12 Scale distortion..............................................................................................................................23 2.13 Conclusion ....................................................................................................................................24 3 Digital conversion of analogue sound......................................................................................................25 3.1 The advantages of digital audio..........................................................................................................25 3.2 Technical restrictions of digital audio - the “power” element .............................................................26 3.3 Technical limitations of digital audio: the “bandwidth” element ........................................................28 3.4 Operational techniques for digital encoding .......................................................................................30 3.5 Difficulties of “cloning” digital recordings ..........................................................................................30 3.6 Digital data compression ....................................................................................................................33 3.7 A severe warning................................................................................................................................35 3.8 Digital watermarking and copy protection..........................................................................................37 3.9 The use of general-purpose computers...............................................................................................38 3.10 Processes better handled in the analogue domain .........................................................................39 3.11 Digital recording media .................................................................................................................40 4 Grooves and styli.....................................................................................................................................42 4.1 Introduction .......................................................................................................................................42 4.2 Basic turntable principles ....................................................................................................................43 4.3 Pickups and other devices ..................................................................................................................44 4.4 Conventional electrical pickup considerations.....................................................................................45 4.5 Operational procedure for selecting a stylus.......................................................................................47 4.6 U-shaped and V-shaped grooves .......................................................................................................48 4.7 The principle of minimising groove hiss ..............................................................................................52 4.8 “Soft” replay styli...............................................................................................................................53 4.9 “Hard” replay styli .............................................................................................................................55 4.10 Stereo techniques..........................................................................................................................57 4.11 “Elliptical” and other styli..............................................................................................................59 4.12 Other considerations .....................................................................................................................61 4.13 Playing records backwards ............................................................................................................63 4.14 Half-speed copying .......................................................................................................................65 4.15 Distortion correction......................................................................................................................65
Page 1: MANUAL OF ANALOGUE SOUND RESTORATIO
Page 5 and 6: Analogue Sound Restoration Techniqu
Page 7 and 8: vii Analogue Sound Restoration Tech
Page 9 and 10: Acknowledgements Few types of tortu
Page 11 and 12: In many other cases, we are compara
Page 13 and 14: the principles, and leave operators
Page 15 and 16: for us. But few people appreciate t
Page 17 and 18: knowledge. To be brutal about it, a
Page 19 and 20: 3. Present-day analysis of survivin
Page 21 and 22: assess the costs of storing the ori
Page 23 and 24: 2.4 Restricting the bandwidth With
Page 25 and 26: Sound Archive, we have an interest
Page 27 and 28: 2.8 “Partially objective” copie
Page 29 and 30: This writer happens to believe that
Page 31 and 32: commercial electrically-recorded di
Page 33 and 34: Unfortunately, such misunderstandin
Page 35 and 36: the noise), but to add the dither w
Page 37 and 38: equired extra bits. (SACD needs sli
Page 39 and 40: strip off the pre-emphasis flag, an
Page 41 and 42: The “advantages” of lossy digit
Page 43 and 44: copyright software evaporate. But t
Page 45 and 46: All this is quite apart from a mach
Page 47 and 48: equipment (section 2.11), and becom
Page 49 and 50: 4 Grooves and styli 4.1 Introductio
Page 51 and 52: open saucer of lukewarm water near
Page 53 and 54:
away from the turntable centre. Thi
Page 55 and 56:
4.6 U-shaped and V-shaped grooves I
Page 57 and 58:
If one tries to cut a groove of U-s
Page 59 and 60:
possible to make the polishing-beve
Page 61 and 62:
- exactly where steel and jewel sty
Page 63 and 64:
From 1953 to 1959, the British Stan
Page 65 and 66:
no cantilever at all, so when the c
Page 67 and 68:
angle. It may be necessary to “mi
Page 69 and 70:
Although my next point is not capab
Page 71 and 72:
Unfortunately the author simply doe
Page 73 and 74:
only hope for removing them without
Page 75 and 76:
For other discs, the present-day tr
Page 77 and 78:
4.17 Electronic click reduction The
Page 79 and 80:
whilst keeping the waveform, we mus
Page 81 and 82:
un them all in real-time. This help
Page 83 and 84:
tolerance to background-noise have
Page 85 and 86:
wanted sound from two copies. No
Page 87 and 88:
23: Girard and Barnes, “Verticall
Page 89 and 90:
that “Pictures are King,” and s
Page 91 and 92:
5.3 History of speed-control in vis
Page 93 and 94:
films. This was so such films could
Page 95 and 96:
Finally, there are a few anomalous
Page 97 and 98:
then ran at these speeds, which wer
Page 99 and 100:
The next complication is that acous
Page 101 and 102:
to collect evidence of the performa
Page 103 and 104:
frequency is 60Hz. If it is recorde
Page 105 and 106:
the documentation can be a very use
Page 107 and 108:
6.2 A broad history of equalisation
Page 109 and 110:
frequency range to give acceptable
Page 111 and 112:
frequency response to 15kHz; it is
Page 113 and 114:
cassettes, and relatively few discs
Page 115 and 116:
Section 6.8 (plus others such as st
Page 117 and 118:
extends all the way up to 20kHz, an
Page 119 and 120:
It isn’t usually possible to defi
Page 121 and 122:
electrical property of wire I menti
Page 123 and 124:
This sounds truly horrible today, a
Page 125 and 126:
There was an increase at high frequ
Page 127 and 128:
The world’s first frequency recor
Page 129 and 130:
6.22 Summary of equalisation techni
Page 131 and 132:
6.24 Recognising recordings made on
Page 133 and 134:
published in Britain in August 1929
Page 135 and 136:
field magnet, but by 1934 a version
Page 137 and 138:
6.33 How to recognise Blumlein cutt
Page 139 and 140:
6.39 Summary of how to equalise “
Page 141 and 142:
M.S.S cutterheads were comparativel
Page 143 and 144:
6.47 The Marconi system There is a
Page 145 and 146:
efer you to the summary in section
Page 147 and 148:
D = Decca, Raynes Park H = British
Page 149 and 150:
upwards). Centre-start was abandone
Page 151 and 152:
Prototype Type Ds were used from th
Page 153 and 154:
Transcription Service intended the
Page 155 and 156:
Some manufacturers consistently adv
Page 157 and 158:
3. Published frequency responses, e
Page 159 and 160:
tape was used for carrying calibrat
Page 161 and 162:
two time constants at about 80 and
Page 163 and 164:
said that the graph in Ref. 43 sugg
Page 165 and 166:
4- to 5-db increase in response at
Page 167 and 168:
Ref. 9: Harry F. Olson and Frank Ma
Page 169 and 170:
55: G. A. Briggs, “Sound Reproduc
Page 171 and 172:
without making the checks first, we
Page 173 and 174:
7.3 Bias The solution to hysteresis
Page 175 and 176:
frequency response is usually consi
Page 177 and 178:
For many years, the standard answer
Page 179 and 180:
The CEDAR “azimuth corrector” w
Page 181 and 182:
published by the IEC in 1966), but
Page 183 and 184:
So far we have been talking about o
Page 185 and 186:
I would recommend that an archive s
Page 187 and 188:
order to restore the original sound
Page 189 and 190:
meant inferior high-frequency respo
Page 191 and 192:
mentioned above, we are more likely
Page 193 and 194:
8: Stanley P. Lipshitz and John Van
Page 195 and 196:
Thousands of improvements were prop
Page 197 and 198:
Somewhat more complex types of soun
Page 199 and 200:
transferred as it is without any ph
Page 201 and 202:
Therefore, it might well be advisab
Page 203 and 204:
9 Reciprocal noise reduction 9.1 Pr
Page 205 and 206:
the “CX” system is specifically
Page 207 and 208:
system became generally available,
Page 209 and 210:
decide whether Dolby B has been use
Page 211 and 212:
compression was effective across th
Page 213 and 214:
noise reduction system in Germany a
Page 215 and 216:
Careful level alignment is necessar
Page 217 and 218:
Characteristic “A” was optimise
Page 219 and 220:
This is one of the areas in which y
Page 221 and 222:
alternative restoration processes c
Page 223 and 224:
processing technique which has much
Page 225 and 226:
design. Thus it is absolutely vital
Page 227 and 228:
Shortly afterwards, “CinemaScope
Page 229 and 230:
published with it. A point-source s
Page 231 and 232:
etween the left-front and right-fro
Page 233 and 234:
In the film world, it can also be a
Page 235 and 236:
hand groove wall with the usual equ
Page 237 and 238:
of the original four-channel images
Page 239 and 240:
10: L. F. Rider, “Magnetic Reprod
Page 241 and 242:
Hardly any of the necessary apparat
Page 243 and 244:
content), audible “sidebands” o
Page 245 and 246:
anomalies by operating his pot slow
Page 247 and 248:
With the advent of rock music from
Page 249 and 250:
Fig. 10.2 5 depicts some steady-sta
Page 251 and 252:
You can sometimes detect a limiter
Page 253 and 254:
many seconds of music at reduced po
Page 255 and 256:
REFERENCES 1: Peter Ford, in his ar
Page 257 and 258:
But I agree it might not be ethical
Page 259 and 260:
eight and eleven degrees.” (I sha
Page 261 and 262:
ecame a “three-minute sound-byte
Page 263 and 264:
Unfortunately, it proved impossible
Page 265 and 266:
(1) Quantify the bass-cut by listen
Page 267 and 268:
Most of the surviving metal horns a
Page 269 and 270:
sound to reverberant sound from the
Page 271 and 272:
12.16 Joining three or more horns S
Page 273 and 274:
to Brahms. That was on 18th June 19
Page 275 and 276:
However, these analogies all depend
Page 277 and 278:
12.23 Practicalities of acoustic re
Page 279 and 280:
The first point is that many early
Page 281 and 282:
copied through “an Auxetophone”
Page 283 and 284:
For the fundamental resonances, the
Page 285 and 286:
20: For the Columbia pattern, see P
Page 287 and 288:
gramophone turntables. The two domi
Page 289 and 290:
usually under different catalogue n
Page 291 and 292:
For some years, microphones suffere
Page 293 and 294:
acoustics. Too much of the first tw
Page 295 and 296:
was a wrong note. For a three-month
Page 297 and 298:
afraid that’s right. Seven-inch p
Page 299 and 300:
“floor manager,” although I do
Page 301 and 302:
We saw in the previous section that
Page 303 and 304:
ecordings to be changed. After the
Page 305 and 306:
different classes of artist, togeth
Page 307 and 308:
POP "SINGLE" and POPULAR 12" LP PRI
Page 309 and 310:
13.10.7 Pre-recorded tapes and cass
Page 311 and 312:
only £250. If you’re a computer
Page 313 and 314:
Inc. provided a great deal of acous
Page 315 and 316:
ehind Western Electric, and many ci
Page 317 and 318:
In section 13.4 above I considered
Page 319 and 320:
cause considerable overloads. Withi
Page 321 and 322:
switching was arranged so the louds
Page 323 and 324:
13.20 The influence of naturalism R
Page 325 and 326:
Appendix 1. Preparing media for pla
Page 327 and 328:
Many cylinders are made of material
Page 329 and 330:
the basic principle of using the lo
Page 331 and 332:
Broken Records Quite honestly, the
Page 333 and 334:
individual tracks and the recorded
Page 335 and 336:
Appendix 2: Aligning analogue tape
Page 337 and 338:
e fully de-gaussed before mounting
Page 339 and 340:
its catalogue-entry), so future eng
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