Manual of Analogue Sound Restoration Techniques
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MANUAL OF ANALOGUE SOUND RESTORATION TECHNIQUES by Peter Copeland The British Library 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 Analogue Sound Restoration Techniques CONTENTS 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 iii Analogue Sound Restoration Techniques 4.16 Radius compensation ....................................................................................................................67 4.17 Electronic click reduction ...............................................................................................................70 4.18 Electronic hiss reduction ................................................................................................................74 4.19 Eliminating rumble ........................................................................................................................76 4.20 De-thumping ................................................................................................................................76 4.21 Future developments.....................................................................................................................77 4.22 Recommendations and conclusion ................................................................................................78 5 Speed setting...........................................................................................................................................81 5.1 Introduction .......................................................................................................................................81 5.2 History of speed control .....................................................................................................................82