The wide-ranging scope of this book illustrates the great variety of disciplines and institutions which owe much to sound recording or archives for their essential stimulus. Indeed, without sound recording and sound archives, it would be hard to imagine some disciplines ever existing in their modern form. Although the problems peculiar to each individual subject are and will remain the prime concern of scholars in those fields, all need to consider the basic technical requirements and the physical conditions necessary if acoustic source material is to be produced and to remain unspoilt for posterity.
This chapter, therefore, is aimed at the technical layman - such as the scholar drawing up a research programme or planning a sound archive - so that he might have some idea of the technical and financial implications of his plans and to ensure that, from the very beginning, he seeks the co-operation or at least the constant advice of technical experts. 1
If we are to establish what problems have to be overcome in sound recording and sound archives, we must first know something about the nature of sound itself. The term 'sound' is generally understood to mean periodic oscillations in air pressure, but for our purposes (with the exception of some bio-acoustic matters) it is sufficient to consider sound simply in terms of human hearing. In humans, hearing sensitivity starts at 16 cycles per second (Hertz, Hz) and extends to an upper limit of 20,000 Hz (20 kHz). Each doubling of audio frequencies is called an octave and the range of human hearing covers about ten octaves. With regard to different sound levels, human hearing has an extensive range. Hearing sensitivity begins at a sound pressure level of 2.10-4 micro-bars and extends to as high as 6.102 micro-bars, at which point the sensation of hearing becomes painful. The ratio of these sound pressure levels, which we term the 'dynamic range', is about 1:3,000.000 or l30dB2. All acoustic phenomena, whether a tone, a sound, exotic music, speech or any sort of noise, are made up of quite individual patterns of oscillation each of which can comprise a variety of partial oscillations but which can all be expressed in the fundamental parameters of frequency (= cycles per second or Hz) and amplitude (sound pressure level, expressed as dB).
By a transformation process, sound recording has to convert these parameters into a medium in which the function of time is rendered as a function of space, i.e. every moment in a sonic event has to correspond to a particular point on a recording.
Old phonographs and the early gramophones used to do this mechanically. Vibrations in the air were captured in a horn, exciting a membrane which in turn set in motion a stylus which left modulations on a revolving cylinder or plate, each modulation corresponding to the vibrations of the membrane and the air. The process of reproducing the sound simply involved reversing the procedure. The modulated groove moved a needle which then caused a membrane to vibrate and the vibrations would be amplified and made audible by the horn. In time electronic methods of recording and reproduction came to be used; the air vibrates the membrane of a microphone which then transforms the vibrations into an analogous alternating current. After precise amplification, this drives an electric cutting head. In reproducing the sound, we nowadays use electro-dynamic or electro-magnetic sound pick-ups which convert the modulation of the record groove into an analogous alternating current. By means of an amplifier, this will then drive a loudspeaker or headphones, which convert the alternating current back into air vibrations. The disc itself has not changed in principle since it was originally introduced.
In magnetic sound recording, the sound is stored on a magnetic tape. The alternating current from the microphone is converted in the machine's recording head into an alternating magnetic field. The tape, moving at a constant speed across this recording head, has each particle stored within its coating re-arranged in accordance with the alternating field. To reproduce the sound, the magnetic field fixed on the tape produces an alternating current as it passes across the replay head and, suitably amplified, is converted into sound by the loudspeaker. The process functions that much more precisely the more linear the system or, to put it another way, the less distortions there are. These distortions can be classified as three different types:
In addition to these distortions there is the unavoidable noise which we find in every link in the chain and which occurs particularly in the sound carrying medium itself, limiting the dynamic range which can be stored. Despite all the technical progress which has been made since sound recording was invented, there is still no system so perfect that distortion will not occur. Even though there are no difficulties nowadays in converting and storing the whole audible frequency range, non-linear and modulation distortions are still with us. More important, with analogue recording techniques only 60 of the 130dB dynamic range of human hearing can be stored (although with the introduction of digital technology the upper limit of this can be raised to 96dB).
In view of what we shall see can be quite considerable outlays for machinery, servicing, tapes and their care and storage, we must explain why this cost-intensive standard is necessary for sound recording and archiving. In contrast to the written and printed word which reproduces a verbalised mental process by a series of representational symbols, a sound recording documents a physical event which can be repeated at any time after the event itself. A certain amount of redundancy is intrinsic in speech and writing and - without any real detriment to communication - letters, words, even whole clauses can be omitted. The essential value of a sound document, however, lies in the very information which it supplies over and above what can be transcribed; such as form and variations in tone, manner of speech, or - in the field of music - the timbre, the performance, the subtleties of rhythm. Here, too, we see more clearly that musical notation provides no more than a framework, just a small part of the total musical message. In the case of a noise, however, written symbols cannot provide an adequate substitute for any part of a sound recording. It is the very information which a transcription simply cannot convey, which provides the criteria and the fundamental argument for high quality sound recording. If, for any reason, the additional information supplied by a sound recording is considered worthless, then the recording is no more than an intermediary substitute for a written record and is not worth keeping. Merely making a voice intelligible or a melody clear enough to be transcribed should not become the sole criterion for technical standards in sound recording. Rather, it should ideally be a question of exhausting all available means to obtain the optimum quality of recording. The value of this ideal is further underlined by the fact that more and more scholars in various fields (musicology, linguistics, psychology) are endeavouring to make this element in sound recording which transcends writing, a subject for serious research.
It must not be concluded, however, that an ideal recording technique will necessarily produce an ideal recording in practice, for an array of technical gadgetry may end up distracting and disturbing the subject being recorded. Careful consideration must be given in every case to producing a compromise between the requirements of technical precision and the need for equipment to be unobtrusive, together with all the implications this may have for the choice of equipment and the resulting recording standards.
The question as to whether existing historical recordings are worth retaining despite their technical shortcomings is something which must be decided after consideration of the contents in each case, but a decision to retain them should not lead us to the conclusion that we may abandon the idea of trying to obtain the highest possible standard of recording in new projects.
In all areas of making original recordings and producing archival copies, the use of equipment of a professional or, at the very least, semi-professional standard is vital. By professional equipment we mean the sort which comes up to modern standards of technology, which will guarantee a minimum of distortion and which will be sturdy enough to continue producing recordings of the highest standard after hundreds and even thousands of hours of operation. By semi-professional equipment we mean the sort designed for the discerning amateur which, in its technical performance, will almost if not totally equal that provided by professional equipment. Of course, semi-professional equipment is not as sturdy in its construction as the professional variety and its performance will decline after extensive use.
Above all, these basic principles apply to the tape recorder which is the vital organ of the technical system in all modern research programmes. If it is at all possible financially, both stationary and portable equipment should be of the professional kind. In view of the small number of companies which deal in equipment of this class, and of the comparable price-to-performance ratio of different products, the choice of a specific make is not critical. From the point of view of efficiency, however, it is best to choose a manufacturer with outlets across the country or throughout the region as this will make servicing and the supply of spare parts that much easier. This generally means using the makes and types of equipment used in local or national radio stations. This approach is particularly recommended for countries outside Europe, if one is to avoid the risk of recording sessions being held up for several weeks when equipment breaks down. Of course, semi-professional equipment can also be used for recording but any savings on purchase costs must in the long run be offset against higher outlays on servicing and repairs. However, these cheaper types of equipment may be used in cases where less precise copies of high quality recordings suffice, such as in monitoring. 1
Of all audio equipment, the tape recorder requires the most thorough maintenance. This is because each individual machine has to be very carefully tuned to match the tapes compatible with it, if the optimum performance is to be obtained from both together. With continuing use the tape heads are gradually worn down, impairing the performance, and regular adjustment is absolutely vital if the best possible quality is to be retained. Moreover, electrical parts can, without any warning, become defective regardless of how long they have been in use and it is essential that tape recorders and the adjustments made for the tapes used on them should be continually monitored. In general, the following service schedule might be used as a reasonable guideline for professional equipment:
Daily (or every time a machine is used): check the frequency response and carry out an auditory test.
Weekly: clean and demagnetise the tape heads and tape paths.
Two monthly (or after every 50 hours use): carry out a full service.
In the case of semi-professional equipment (especially with machines which receive rather rough handling or are used to record a unique or rare occasion) it is advisable to carry out the above procedures at more frequent intervals. A full service on a professional piece of equipment will take between one and two hours (as long as no serious repairs are necessary) but about twice as long is to be spent servicing a semi-professional set. If it is at all possible financially, institutions should employ their own well qualified audio service technician for this work. Even if an institution has only a small amount of equipment such a technician, qualified in the right field, can be given the job of producing copies and looking after the collection. In this way institutions will avoid the need to rely on the often shoddy workmanship of servicing firms and at the same time find it easier either to carry out or to supervise the extensive servicing of equipment necessary in order to maintain archival standards. A written record should also be kept of this work. Managing all this, of course, requires a whole series of test apparatus and tools and, last but not least, a workshop.2 Lack of the necessary financial resources or shortage of skilled technicians may make this impossible, in which case one should always try to work in close co-operation with similar institutions which share the same service requirements and with whom a solution to one's needs might more easily be achieved. Alternatively, one might enlist the help of local or national radio stations.
Microphones should be chosen with great care. Not only do they have to satisfy specific technical requirements, they should also be tested in a properly equipped workshop whenever they have been extensively used (once a year at least and whenever they have been dropped or similarly mistreated). Here again, if the necessary facilities are not otherwise available, institutions of a similar nature should work together or, where there are no other similar institutions, radio organizations should be consulted for technical expertise and advice.
If the highest standards are to be maintained, then the choice of tapes and tape formats is scarcely less important than the choice and maintenance of recording equipment. Because of its sturdy nature and its low sensitivity to humidity and temperature, and because it presents the least mechanical problems, the tape most widely used nowadays for archival purposes is polyester tape with a thickness of 52 micro-metres (1.5 mil). Several varieties of tape display good electro-magnetic qualities, are not significantly prone to print-through and are, therefore, suitable for archival purposes. For recording outside the studio long-play or double-play tapes are often the best sort to use because of the length of recording time they give, but care should be taken to make sure that these records are transferred to archival tape as soon as possible. It is impossible to say that anyone particular tape is 'the best', and the choice of tapes is usually a question of compromise between availability and price. As with the choice of equipment, one should bear in mind when choosing tapes, how many other similar institutions or radio stations use the same type. Furthermore, one should generally choose tapes which are likely to be available on sale for as long as possible, so that recording equipment does not have to be continually re-adjusted to compensate for different sorts of products. For the same reason it is advisable to purchase a large stock -about a year's supply -in advance and to ask for a batch from the middle of a production run. Care should be taken with new varieties of tapes, as the improved electro-magnetic qualities of a tape can often be accompanied by a fall-off in mechanical quality (such as its resistance to oxide shedding), at least during the period when a new tape is being brought onto the market. It makes better sense, therefore, to choose a somewhat older but proven product rather than risk losing valuable source material by using poorly tested products.
As efficient sound recording is a basic requirement for sound archives, it follows that high standards should be observed when choosing tape formats. The recording speed for original recordings and archival copies should never be less than 19 cm/s. For mono recordings one should use full-track, while for stereo recordings, halftrack should be used. For evaluation work and for distribution the expense can, of course, be tailored according to the requirements and for certain types of work compact cassettes are quite adequate in the quality they provide.
In presenting the arguments for high standards in recording we saw that sound recordings, unlike written records, contain no superfluous matter but that every detail is a source of information. In a book, a spot of fungus on a page will generally not hinder the reader and at worst may reduce the volume's commercial value, but the slightest damage to a sound recording immediately results in a loss of information. Its physical vulnerability dictates the precautions which we need to take if we are to ensure the preservation of acoustic source material. 1
Before considering other risks to sound carrying media we must first consider the problems of decrease in quality as a result of normal use. Disregarding the damage done to recordings by careless handling, the loss of quality through normal use is relatively high in the case of mechanical sound carrying media. Because of the friction between stylus and record, with time the groove becomes worn and the signal distorted. The degree of wear and tear involved depends on various factors, but above all on the condition and adjustment of the record player. The recorded signal and the material of which the record is made are also important factors, so that no matter how careful one might be the risk of damage can still be relatively high. These risks are appreciably less in the case of magnetic recordings and, provided excellent playback facilities and modern tapes are used, it is safe to say that changes in the signal in normal playback will be minimal. There is always the danger that tape oxide might sometimes be rubbed off, especially when older tapes are wound at high speed. In particularly bad cases one must take special care by making safety copies, but generally it is sufficient simply to wind at a slower speed.
The effects of temperature on sound carrying media depend on the material involved. In the case of shellac and modern vinyl records and the nowadays rather rare PVC tapes, temperatures above 500 C are considered a risk. The old acetate tapes, which are no longer produced, and the modern polyester tapes can withstand temperatures well over l000C. High temperatures, however, will increase print-through on tapes and continual changes in climatic conditions are also to be avoided; the optimum temperature for an archive is 200 ± 30 C, although print-through can be kept to a minimum in rarely used stores for security copies by keeping temperatures at a level of 100C. It should also be noted that heating devices, lighting and sunlight can also be damaging, even when temperature controls are used. The field researcher operating in tropical climates can provide some protection for his tapes and films by keeping them in polystyrene containers.
Only shellac records are immediately at risk from high humidity. The old acetate and cellulose tapes, on the other hand, shrink and warp if storage conditions are too dry. Micro-organisms such as fungus thrive in high humidity and quickly attack both magnetic and mechanical sound carrying media altering the surfaces to such an extent that the record content may be partially or even totally ruined. Relative humidity should therefore be kept to a level of 50% ± 10%. Humidity is particularly important to researchers working in tropical regions, where valuable original recordings can be protected by frequently exposing them to the air and storing them together with moisture absorbent silica gel.
On records, dirt in its many forms produces the well-known crackle effect. With tapes it leads to 'drop outs', as the contact is lost between tape and tape head. Dust should, therefore, always be avoided and, equally, one should never touch the surface of a record or tape as this can also cause dirt to stick to it. Adhesives of all kind, especially inadequate splicings, should be removed if present and otherwise generally avoided. Before adopting a particular method of cleaning record or tape surfaces, one should always make a thorough check of the available literature on the subject and test the methods properly beforehand. Good packaging, properly sealed work rooms, archive areas which can be easily cleaned and with dust filters fitted to climate controls should provide a good protection against dust.
Defective spools and uneven winding can cause tape warping as also can bad packaging and incorrect storage. Both records and tapes should be stacked absolutely vertical when in store; if they are kept in a leaning position for long periods, they can become permanently warped and so this too should be avoided. Records may also be stored in suspended position, while any inserts - such as textual material - which can cause them to warp, should be kept separately.
A well-known and, as we shall see, over-rated cause of damage to tapes in store is the occurrence of print-through. This term is used to describe the echo effect resulting from magnetic interaction between two adjacent layers of tape on a reel, thus producing the effects known as pre-echo and post-echo. The degree of print-through mainly depends on the characteristics of the individual tape, on tape thickness, temperature and period of storage. However, the echo signal - unlike the basic recording signal - is unstable and can easily be greatly reduced by mechanical means, such as rapidly rewinding the tape. This is confirmed by the results of recent tests. 2 The problem of print-through, therefore, is one which can be ignored as long as tapes are chosen and stored correctly, are rewound once a year and kept alternately on the take-up spool (or 'tails out' position) and the feed spool (or 'tails in').
One should not underestimate the dangers to tapes from magnetic fields. Tapes should, therefore, be kept well away from dynamic microphones and headphones, as well as from loudspeakers and electronic measuring instruments. Permanent magnetic fields, which are a particular risk to tapes during play-back, can also build up on tape heads and tape guides. Regular demagnetisation is, therefore, a vital part of any service schedule. One should also make certain when fitting out storage areas that there are no high voltage electricity cables, power transformers or lightning conductors in the vicinity which might be dangerous sources of magnetic fields.
To complete the picture, it must also be said that one should consider not only the specific problems mentioned above, but also the more general ones such as security against theft, fire and flooding.
Magnetic recording media (tapes) with the following base materials:
acetate-cellulose (AC, no longer used)
polyvinylchloride (PVC, rarely used)
polyester (PE)
As we have seen, all forms of sound recordings are extremely vulnerable and we should, therefore, consider a few basic principles and organizational methods aimed at minimizing the intrinsic problems involved.
Even if all the measures mentioned under section 4 are observed, accidental damage can never be ruled out. It is, therefore, necessary to develop a policy which will minimize - if not eliminate - any remaining risks. The main principle of such a policy is to keep -if at all possible - two high quality copies of each item in separate locations: one in the storage area of the sound archive itself; the other in a security vault well away from the archive's premises.
Wherever original recordings are made in a studio, standard archival tape should be used. Ideally two recordings should be made at the same time: one should function as the archival master to be retained in the archive itself. The second should function as a security copy to be stored in the security vault. The archival master should only be used occasionally, while in those cases where frequent use or in-depth evaluation is foreseeable, an additional (working) copy should be made. This copy may be of lower fidelity and even a cassette copy may serve for many routine archive purposes.
Original recordings made on portable equipment in the field, are rarely recorded on standard archival tape. It is therefore necessary to copy these long-play or double-play original tapes onto archival tape which then will serve as archival masters. If economies have to be observed then as a compromise the original tapes may, after copying, function as security copies, although it must be borne in mind that LP or DP tapes are not the most suitable for security purposes.
The production of archival masters and security copies should always be done with utmost technical care avoiding any element of subjective filtering or other aesthetic treatment. Fast copying techniques always affect the quality and therefore should be used - if at all - only for the production of working copies where a lower quality is acceptable. Every archival master tape should begin with test tones which facilitate the production of further copies and make it possible to conduct subsequent quality control inspection of the tapes. They also serve for short checks of the equipment while it is used. 1
The same principles of security also apply to records. Duplicates should be kept and - for security purposes - be stored at separate locations. Because of the higher vulnerability of records, the archival master should always be a tape copy while the record itself should only be used if the archival master is accidentally destroyed.
All storage areas, the one in the archive itself as well as the separate security vault, should be equipped with full temperature and humidity control (especially under tropical and subtropical conditions). The high cost outlay involved will often suggest co-operation with other sound archives in the same country or region. It may, therefore, be wise to establish as few independent sound archives as possible and to concentrate financial resources as well as organizational and technical skill. At university level, at least, only one unit should be established and professionally equipped and this should maintain co-operation with all research bodies that have an interest in the production and use of sound recordings.
If proper technical quality control is to be maintained, then written records should be kept of all equipment used for recording and copying. A note of the dates on which the recordings were made and the results of tests conducted should also be kept. This information together with the written reports on equipment tests, make it possible to carry out proper quality evaluations of copies. This is especially important in the light of the increasing work being done in all fields in acoustic analytical evaluation, since a sound recording essentially provides a measurement of a physical process whose accuracy or inaccuracy has to be known. It is also useful to keep test reels of each of the various sorts of tapes or batches of tape used, with recorded signals and a length of unused tape for future inspection and test.
Finally, it should be a basic principle of routine organizational security that only archival staff be allowed to handle original tapes, archival and security copies. Only by strict observation of this principle and by careful choice of staff who believe in precision in all things, can damage to the archival holdings be minimised.
In this chapter we have tried to show the technical layman who has to produce, accession and evaluate sound recordings the basic physical and technical framework within which he must operate. He should not assume that he no longer needs to study the relevant literature or seek technical advice. This chapter, however, should help him to take the right direction from the beginning and to approach the responsible financial authorities for the necessary funds. Let us not forget that, amidst all our considerations, it is the physical preservation of valuable acoustic source material and an irreplaceable heritage which is at stake.