MANUAL OF ANALOGUE SOUND RESTORATION ... - British Library

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I shall ask you to remember the hassles of copy-protection (section 3.8 above), and next I will state a few principles you might consider when making your decision. They are based on practical experience rather than (alleged) scientific research. (1) It is always much easier to reproduce widely-used media than specialist media. It is still quite cheap to install machinery for reproducing Edison cylinders, because there were over a million machines sold by Edison, and both enough hardware and software survives for experience also to survive. (2) The blank destination-media should not just have some “proof” of longevity (there are literally thousands of ways of destroying a sound recording, and nobody can test them all)! Instead, the physical principles should be understood, and then there should be no self-evident failure-mechanism which remains unexplained. (For example, an optical disc which might fade). (3) The media should be purchased from the people who actually made them. This is (a) so you know for certain what you’ve got, and (b) there is no division of responsibility when it fails. (4) Ideally the media (not their packaging) should have indelible batch-numbers, which should be incorporated in the cataloguing information. Then when an example fails, other records from the same batch can be isolated and an emergency recoveryprogramme begun. (5) On the principle “never put all your eggs into one basket,” the digital copy should be cloned onto another medium meeting principles (2) to (4), but made by a different supplier (using different chemicals if possible), and stored in a quite different place. So, after a long time examining operational strategy, we are now free to examine the technicalities behind retrieving analogue signals from old media. REFERENCES 1: anon, “SDMI chooses MusiCode from Aris to control Internet copying” (news item), London: One To One (magazine), Issue 110 (September 1999), page 10. 2: ibid, pages 73-74 and 77. 3: Barry Fox, “technology” (article), London: Hi-Fi News & Record Review (magazine), Vol. 44 No. 10 (October 1999), page 27. 41
4 Grooves and styli 4.1 Introduction This chapter will be about “mechanical” sound recordings, in which the sound waves were translated into varying waveshapes along the length of a spiral groove. These waves are nearly always “baseband” - that is, the sound frequencies were recorded directly, instead of being modulated onto a “carrier frequency” in some way. The principal exception will be quadraphonic recordings using the CD-4 system, which I shall leave until we explore spatial sounds in section 10.16. A century of development lies behind sound recording with mechanical techniques. The technology is unlike any other, since a frequency range of some ten octaves might be involved, with signal-to-noise ratios in the upper-sixties of decibels. Thus the powerbandwidth products of the best mechanical recordings can rival anything else analogue technology has achieved. In this chapter I shall be considering the best ways to extract the original sound from disc or cylinder grooves. It will deal with the groove/stylus interface and also electronic techniques for minimising surface noise and distortion. Thus we will have taken the story to the point where electrical waveforms are coming out of a socket in anticipation of adjustments to playing-speed or frequency-equalisation. At this socket we will have extracted all the frequencies from the groove while minimising distortion, and will have reduced the surface noise as far as we can; thus we will have recovered the maximum power-bandwidth product. This is the fundamental limitation. After that we may refine the sound if we want to. It is an old adage that if the groove/stylus interface is wrong, it is pointless to rely on electronics to get you out of your difficulties. I think this is something of an oversimplification, although the basic idea is correct. My point is that we should really work upon the groove/stylus interface at the same time as electronic noise reduction. Some electronic treatments are very good at removing showers of loud clicks, for instance. When this is done, it is then possible to choose a stylus to reduce the remaining steady hiss. Had the stylus been chosen without the de-clicker in place, it might not have been the one which gave the least hiss. This would be wrong, because the current stateof-the-art is that it is much more difficult to approach the intended sound in the presence of steady hiss. Although I shall leave electronic treatments until the sections following 4.15, please remember the two topics should actually go hand-in-hand. And once again, I remind you of the importance of having the best possible originals, as we saw in section 2.6. I shall be making great use of the term “thou” in this chapter. This means “thousandths of an inch”, and has always been the traditional unit of measurement for styli and grooves. In North America, the term “mil” has the same meaning. Although it would be perfectly acceptable to use the metric term “microns”, where one micron is one-millionth of a metre, specialist stylus-makers still speak in “thou”, so I shall do the same. One thou equals 25.4 microns. Two other terms I must define are “tracing” and “tracking.” I do so because many textbooks confuse them. “Tracing” concerns the way a stylus fits into, and is modulated 42
Page 1 and 2: MANUAL OF ANALOGUE SOUND RESTORATIO
Page 3 and 4: CONTENTS iii Analogue Sound Restora
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: equipment (section 2.11), and becom
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
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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
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6.2 A broad history of equalisation
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frequency range to give acceptable
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frequency response to 15kHz; it is
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cassettes, and relatively few discs
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Section 6.8 (plus others such as st
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extends all the way up to 20kHz, an
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It isn’t usually possible to defi
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electrical property of wire I menti
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This sounds truly horrible today, a
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There was an increase at high frequ
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The world’s first frequency recor
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6.22 Summary of equalisation techni
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6.24 Recognising recordings made on
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published in Britain in August 1929
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field magnet, but by 1934 a version
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6.33 How to recognise Blumlein cutt
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6.39 Summary of how to equalise “
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M.S.S cutterheads were comparativel
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6.47 The Marconi system There is a
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efer you to the summary in section
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D = Decca, Raynes Park H = British
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upwards). Centre-start was abandone
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Prototype Type Ds were used from th
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Transcription Service intended the
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Some manufacturers consistently adv
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3. Published frequency responses, e
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tape was used for carrying calibrat
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two time constants at about 80 and
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said that the graph in Ref. 43 sugg
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4- to 5-db increase in response at
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Ref. 9: Harry F. Olson and Frank Ma
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55: G. A. Briggs, “Sound Reproduc
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without making the checks first, we
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7.3 Bias The solution to hysteresis
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frequency response is usually consi
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For many years, the standard answer
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The CEDAR “azimuth corrector” w
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published by the IEC in 1966), but
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So far we have been talking about o
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I would recommend that an archive s
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order to restore the original sound
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meant inferior high-frequency respo
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mentioned above, we are more likely
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8: Stanley P. Lipshitz and John Van
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Thousands of improvements were prop
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Somewhat more complex types of soun
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transferred as it is without any ph
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Therefore, it might well be advisab
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9 Reciprocal noise reduction 9.1 Pr
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the “CX” system is specifically
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system became generally available,
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decide whether Dolby B has been use
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compression was effective across th
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noise reduction system in Germany a
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Careful level alignment is necessar
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Characteristic “A” was optimise
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This is one of the areas in which y
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alternative restoration processes c
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processing technique which has much
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design. Thus it is absolutely vital
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Shortly afterwards, “CinemaScope
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published with it. A point-source s
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etween the left-front and right-fro
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In the film world, it can also be a
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hand groove wall with the usual equ
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of the original four-channel images
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10: L. F. Rider, “Magnetic Reprod
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Hardly any of the necessary apparat
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content), audible “sidebands” o
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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
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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
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eight and eleven degrees.” (I sha
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ecame a “three-minute sound-byte
Page 263 and 264:
Unfortunately, it proved impossible
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(1) Quantify the bass-cut by listen
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Most of the surviving metal horns a
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sound to reverberant sound from the
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12.16 Joining three or more horns S
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to Brahms. That was on 18th June 19
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However, these analogies all depend
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12.23 Practicalities of acoustic re
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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
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gramophone turntables. The two domi
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usually under different catalogue n
Page 291 and 292:
For some years, microphones suffere
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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
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ecordings to be changed. After the
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different classes of artist, togeth
Page 307 and 308:
POP "SINGLE" and POPULAR 12" LP PRI
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13.10.7 Pre-recorded tapes and cass
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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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