This paper presents a methodology for the preservation of audio documents, the operational protocol that acts as the methodology, and an original open source software system that supports and automatizes several tasks along the process. The methodology is presented in the light of the ethical debate that has been challenging the international archival community for the last thirty years. The operational protocol reflects the methodological principles adopted by the authors, and its effectiveness is based on the results obtained in recent research projects involving some of the finest audio archives in Europe. Some recommendations are given for the rerecording process, aimed at minimizing the information loss and at quantifying the unintentional alterations introduced by the technical equipment. Finally, the paper introduces an original software system that guides and supports the preservation staff along the process, reducing the processing timing, automatizing tasks, minimizing errors, and using information hiding strategies to ease the cognitive load. Currently the software system is in use in several international archives.
Computer science offers multiple possibilities to study the fields of humanities: a major topic that has been rapidly growing along the past decades is the implementation of computer engineering in musical cultural heritage, with a particular relation to the audio documents preservation (“ideally, an audio preservation workflow would also involve the services of a specialized programmer” [
Scholars and the general public started paying greater attention to the recordings of musical events and to their value, at a personal/collective level and for cultural/entertainment purposes. However, a systematic preservation and the fruition of these documents is complicated by their diversified nature: recordings contain information on their artistic and cultural existence that goes beyond the audio signal itself. In this sense, a faithful and satisfying access to the audio document cannot be achieved without its associated contextual information, that is, to all the content-independent information represented by the container, the signs on the carrier, the accompanying material, and so on.
In an official technical report, the UNESCO [
The factors that obstruct the safeguard of audiovisual documents are multiple: mainly the massive investment of human and economical resources required by digitization campaigns, not to mention teams with multidisciplinary competences, difficult and expensive to form. As a consequence, today many archives are in fact lacking methodological and technological tools to safeguard adequately their patrimony.
The process of physical degradation that characterizes every type of audio carriers can be slowed down, by means of correct preservation policies, but not stopped. Therefore, the survival of the information contained in the document is possible only renouncing to its materiality, through a constant transfer of the information onto new carriers. Unfortunately the remediation process (the operation of transferring the information from a
As far as audio memories are concerned, preservation is divided in passive (also referred to as preventative preservation) and active preservation, which involves data transfer onto new media. Passive preservation is further divided into indirect (covering the maintenance of proper storage conditions, establishing professional handling procedures, etc.) and direct (the carrier is treated in order to stabilize its physical condition, but its structure and composition are not altered).
It is worth noting that, in the Eighties/Nineties of the 20th century, expert associations were still concerned about the use of digital recording technology and digital storage media for long-term preservation [
For the longest time, the word “archive” has been suggesting images of shelves and books. It is only recently that audiovisual material, first labeled as
In the last thirty years, the awareness for the preservation of audio documents has increased, allowing them in the definition of cultural heritage. At the same time, the debate on the ethics of preservation got more lively and the tools to activate the preservation practices have become richer. More recently, audio recordings have been recognized as an important documentary source for scientific research in the fields of linguistics, history, sociology, musicology, and other disciplines. Their dignity has been equaled to that traditionally reserved to bibliographic sources, revealing once more the centrality of philological problems such as the authenticity and the authority of the documents.
Approaching the archival reality from a viewpoint of the methodological research and of the scientific reflection, the authors have identified some critical situations in the management of the processes involved in the preservation of the audio patrimony. They have tried to propose effective solutions using original software tools, the design of which required (i) a reflection on the relevant characteristics of each type of carrier and (ii) the subsequent definition of a metadata set that meets the requirements of the methodology proposed by the authors in Section
From the viewpoint of the scientific research, these tools fall within the scope of the area of
In fact, the great majority of the operations that characterize the archival routines are highly repetitive, and those involved in the active preservation of audio documents are no exception. As a consequence, the amount of time spent for the processing and the management of electronic files is considerable, and the well-known pathologies of attention related to repetitive activities and/or low level tasks may induce the human operator to introduce errors which have a cascade effect on the workflow, causing the malfunctioning of the algorithms that check the internal consistence of the archive and the algorithms for information retrieval. Also for the long-term maintenance of the archive adequate tools are required, as on the one hand the periodical control of every single documents is not sustainable and on the other hand a sample check is not satisfactory.
In particular, the tools developed by the authors (a) reduce the duration of restoration/remediation sessions, (b) dramatically reduce the time necessary to create the access copies, and (c) they introduce a set of redundant automatized controls that ensure data integrity. PSKit PreservationPanel has been used for the preservation of audio documents in several projects listed in Section
This work is the result of the experience matured in several research/applied projects carried out by the authors on Digital Audio Archives and Audio Access (see Section
After a detailed overview on how this debate evolved since the Seventies inside the archival community on the preservation of audio documents (Section
This section presents the most significant positions of the thirty-year-long debate that was built around the preservation of audio documents. The ethics of preservation is discussed from the viewpoint of the multiple motivations for going digital, which result in different choices on the operational level (see Section
The journal article that started it all in 1980 bore the signature of William Storm, at that time Assistant Director of the Thomas A. Edison Re-recording Laboratory Syracuse University Libraries [
Storm individuated two legitimate directions, two types of re-recording which are suitable from the archival point of view: (1) the sound preservation of audio history and (2) the sound preservation of an artist.
The first type of re-recording (Type I) represents a level of reproduction defined “as the perpetuation of the sound of an original recording as it was initially reproduced and heard by the people of the era.” [
The second type of re-recording (Type II) was presented by Storm as a further stage of audio restoration, as a more ambitious research objective, conceived as a coherent development of Type I: “The knowledge acquired through audio-history preservation provides the sound engineer with a logical place to begin the next step—the search for the true sound of an artist.” Type II is then characterized by the use of “playback equipment other than that originally intended so long as the researcher proves that the process is objective, valid, and verifiable” [
The Guide [
The choice whether or not to compensate for these alterations reveals different re-recording strategies: “historical faithfulness can refer to various levels: Type A the recording as it was heard in its time, which is equivalent to Storm's Type I presented in the previous section; Type B the recording as it has been produced, precisely equalized for intentional recording equalizations, compensated for eventual errors caused by misaligned recording equipment and replayed on modern equipment to minimize replay distortions” [
Type B re-recording defines a historically faithful level of reproduction that, from a strictly preservative point of view, is preliminary to any further possible processing of the signal. These compensations use knowledge which is external to the audio signal; therefore, even in the operations provided for by Type B, there is a certain margin of interpretation because a historical acquaintance with the document is called into question alongside with technical-scientific knowledge. For instance, to individuate the equalization curves of magnetic tapes or to determine the rotation speed of a record. Most of the information provided by Type B is retrievable from the history of audio technology, while other information is instead experimentally inferable with a certain degree of precision. The re-recording work can thus be carried out with a good degree of objectivity and represents an optimal level within which the standard for a preservation copy can be defined.
After having established an operational criterion for preservative re-recordings, based on stable procedures and derived from an objective knowledge of the degradations, Schüller individuated a third level of historically faithful reproduction, type C: “The recording as produced, but with additional compensation for recording imperfections caused by the recording technique of the time” [
The studies of George Brock-Nannestad [
As has been pointed out in the Introduction, the fact that digitization might be the current best solution to the problem of carriers degradation has been gradually accepted by the international community. To date it is widely understood, yet the reasons for “going digital” can differ depending on the archive characteristics, size, and policies. In this sections, the main reasons accounted in [
The first reason for digitization can be enhanced access to materials that were previously unavailable or only partially/locally available. Digitization, in this sense, is part of the democratic considerations promoted by archives, making public records more widely accessible. Access can be permitted to the metadata and/or to the data, enabling/extending the availability to support educational and outreach projects, or a defined stock of research material. Digitization may also be aimed at implementing the “virtual re-unification” of collections and holdings from a single original location or creator now widely scattered, or at creating a single point of access to documentation from different institutions concerning a special subject.
A second reason for “going digital” is to promote and to facilitate the access. The main purpose is to enable the use of material (original manuscripts and archives, maps, museum artifacts, rare books, etc.) that cannot be consulted in its original form other than by visiting its specific repository, because it has been damaged or because it is easier and more productive to access without computer enhancement tools like OCR (Optical Character Recognition) or text encoding for converted texts.
Preservation, on which this paper is focused, appears as the third possible reason for starting a digitization campaign. However, the authors believe that it should be considered a preliminary step to the realization of the other objectives. The main reason is that the documents that are accessed by the final users are the result of a processing chain that usually starts from a digital preservation master, aligned with the highest standards, and aware of the philological questions of accuracy and authenticity.
A central concept in the operational protocol here proposed is the “preservation copy” of an audio document: it consists in an organized data set that groups all the information represented by the source document, stored, and maintained as the preservation master (see Section Physical documentation Photographic documentation Scanned images Data validation Visual inspection Chemical analysis Optimization of the carrier Analysis of the recording format/parameters System setup Replay equipment (e.g., reel-to-reel tape recorder) Remediation equipment (converter, acquisition software, monitoring, etc.) Monitoring Data validation Archival of the source carrier Metadata extraction Completion of the preservative copy.
Scheme of the remediation process, in which three distinct steps can be observed, as well as the set of control procedures applied during the workflow. Each step is articulated in procedures and sub-procedures.
The input of the remediation process is an audio document, and the expected output is its preservation copy—along with the source document ready to be stored again. After the remediation process, the carrier’s condition should normally be better than before, thanks to the restoration to optimize its performance—except for the carriers with a very poor starting condition: these might not endure one/multiple playback sessions and be no longer readable after the process (for these, the optimization of the carrier before playback is crucial since there is only one chance to extract the best signal). In general, source documents should be kept for future comparisons and for other purposes that depend on the evolution of technology and that cannot be predicted to date. “Discarding an original, no matter how many copies have been made, should never be undertaken lightly” [
Direct passive preservation can be carried out only if the main causes of the physical carriers deterioration are known and consequently avoided. We summarize the main risks for the most common categories of carriers: mechanical carriers, magnetic tapes, optical discs, and magneto-optical carriers.
The common factor with this group of documents is the method of recording the information, which is obtained by means of a groove cut into the surface by a stylus modulated by the sound, either directly in the case of acoustic recordings or by electronic amplifiers. Mechanical carriers include phonograph cylinders, coarse groove gramophone, and instantaneous and vinyl discs. Table
Typologies of analogue mechanical carriers.
Carrier | Period | Composition | Stocks |
---|---|---|---|
Cylinder recordable | 1886–1950s | Wax | 300,000 |
| |||
Cylinder replicated | 1902–1929 | Wax and Nitrocellulose with plaster |
1,500,000 |
| |||
Coarse groove disc replicated | 1887–1960 | Mineral powders bound by organic binder (shellac) | 10,000,000 |
| |||
Coarse and microgroove discs recordable (“instantaneous discs”) | 1930–1950s | Acetate or nitrate cellulose coating on aluminum (or glass, steel, card) | 3,000,000 |
| |||
Microgroove disc (vinyl) replicated | 1948–today | Polyvinyl chloride-polyacetate copolymer | 30,000,000 |
The main causes of deterioration are related to the instability of mechanical carriers and can be summarized as follows [
The figure shows an example of impulsive noise (click) in the waveform of an audio signal extracted from a 78 rpm shellac disc. It is clearly visible at second 13.263. Such disturbance can be caused by a speck of dust in a disc groove. Time (seconds) is shown on the
The figure shows an example of broadband noise and impulsive noise in a spectrogram of an audio signal extracted from a 78 rpm shellac disc. Broadband noise is due to the granular nature of the material and its degradation over time. Time (seconds) is shown on the
The basic principles for recording signals on a magnetic medium were set out in a paper by Oberlin Smith in 1880. The idea was not taken any further until Valdemar Poulsen developed his wire recording system in 1898. Magnetic tape was developed in Germany in the mid-1930s to record and store sounds. The use of tape for sound recording did not become widespread, however, until the 1950s. Magnetic tape can be either reel to reel or in cassettes. Table
Types of magnetic tape carriers.
Period | Type of recording | Composition |
---|---|---|
Base: cellulose acetate | ||
1935–1960 | Analogue | Magnetic pigment: Fe2O3 |
Formats: open reel | ||
| ||
Base: PVC | ||
1944–1960 | Analogue | Magnetic pigment: Fe2O3 |
Formats: open reel | ||
| ||
Base: polyester | ||
1959-today | Analogue | Magnetic pigment: Fe2O3 |
Formats: open reel, compact cassette IEC I | ||
| ||
1969–today | Analogue/digital | Base: polyester |
Magnetic pigment: CrO2 | ||
Formats: compact cassette IEC II, DCC | ||
| ||
Base: polyester | ||
1976–1980 | Analogue | Magnetic pigment: SLH Ferro (blue tabs, Type I) and FeCr (red tabs, Type II) |
Formats: Elcaset | ||
| ||
1979–today | Analogue/digital | Base: polyester |
Magnetic pigment: metal particle | ||
Formats: compact cassette IEC IV, R-DAT |
The main causes of deterioration are related to the instability of magnetic tape carriers and can be summarized as follows [
Among the others, some effects can be “drop out” (i.e., the magnetic material fall off the tape); “print-through” (i.e., a condition where low-frequency signals on one tape winding imprint themselves on the immediately adjacent tape windings); “stretch” (i.e., the actual permanent stretching of the polyester caused by too tightly spooling the tape with noticeable pitch dropping).
Table
Recommended climatic storage parameters for mechanical and for magnetic tapes.
Temperature | ±/24 h | ±/year | RH | ±/24 h | ±/year | |
---|---|---|---|---|---|---|
Preservation storage | 5°C < |
±1°C | ±2°C | 30% | ±5% | ±5% |
| ||||||
Access storage | Abo |
±1°C | ±2°C | 40% | ±5% | ±5 |
Optical disc recording technologies are based on the encoding of binary data in the form of
Types of optical discs [
Carrier | Period | Type of recording | Composition |
---|---|---|---|
CD | 1981–today | Digital | Base: polycarbonate |
Reflective layer: aluminium, varnish, inks | |||
| |||
CD-recordable | 1992–today | Digital | Base: polycarbonate |
Reflective layer: gold, silver, varnish, inks | |||
| |||
CD-rewritable | 1996–today | Digital | Base: polycarbonate |
Reflective layer: varnish, inks | |||
| |||
SACD | 1999–today | Digital | Base: polycarbonate |
Reflective layer: silver | |||
Coating: lacquer | |||
| |||
DVDA | 2000–today | Digital | Base: polycarbonate |
Inner layer: aluminium | |||
Outer semireflective layer: gold | |||
Coating: lacquer |
Digital information is pressed into a polycarbonate base, coated with a light reflective layer usually made of aluminum; however, gold and silver are also used. A transparent lacquer is placed over the reflective surface in order to protect it. Most optical discs do not have an integrated protective casing, and therefore they are easily subject to scratches, fingerprints, and other environmental problems, described in Appendix C of [
Table
Recommended climatic storage parameters for optical media.
Temperature | ±/24 h | ±/year | RH | ±/24 h | ±/year | |
---|---|---|---|---|---|---|
Preservation storage | About 20°C | ±1°C | ±3°C | 40% | ±5% | ±5% |
The behavior of digital optical media in their physical decay appears to reflect their “binary” nature: a disc will be either playable or unplayable, with very little difference in between (compared to the corruptions that can affect magnetic tapes and that result in many levels of seriousness). When a disc is corrupted but still playable, the extracted signal will be often characterized by impulsive noises, sometimes intermitted with entire sets of consecutive missing samples. Since monitoring during the process of signal extraction is not provided for this type of carriers (see Section
Sony announced the MiniDisc (MD) audio format to appear in 1992, promising a combination of CD clarity with cassette convenience. Despite the expectations, MiniDiscs did not do very well on the market and were eventually overshadowed by solid-state memory audio recorders. Altogether, the format survived two decades: Sony announced that the development of MD devices will be halted in March 2013.
The data is memorized in two steps: a laser heats one of the sides of the disc, making the material in the disc susceptible to a magnetic field, and on the other side, a magnetic head alters the polarity of the heated area. Then the data is accessed with the laser alone: taking advantage of the magneto-optic Kerr effect (MOKE), the player senses the polarization of the reflected light and is able to read the binary values.
Table
Types of MiniDiscs [
Carrier | Period | Type of recording | Composition |
---|---|---|---|
MD replicated | 1992–2013 | Digital | Base: polycarbonate |
Reflective layer: aluminium, varnish | |||
| |||
MD recordable | 1992–2013 | Digital | Base: polycarbonate |
Magneto-optical layer: ferromagnetic material | |||
Reflective layer: aluminum |
With regards to degradation, MiniDiscs are mainly threatened by dust and dirt deposits especially within the housing, and in general they share the same problems of optical discs.
This section provides more details on the operational protocol introduced in Section
The protocol has been assessed and refined during a number of research projects involving some of the finest audio archives in Italy (see Section
Before the remediation process starts, it is necessary to define a preservation schedule. This depends on the number of documents, on their state of preservation, on the archive priorities/policies, and on other factors. The preservation schedule is usually defined after the study of the characteristics and of the state of preservation of the carriers since these elements weigh in the decision. Determining a satisfactory schedule is not straightforward and always requires a compromise, as the criteria to consider are often in contrast. It is revealed that the criteria suggested by the main institutions in the field have a different priority.
IFLA (International Federation of Library Associations and Institutions) [ content: intellectual value of materials, their historical, scientific, and cultural significance (unique sources must have priority); demand: priority is given to materials in constant demand; condition: fragile and damaged unique materials (restoration procedures may be needed before the transfer);
IASA (International Association of Sound and Audiovisual Archives) [ documents in immediate risk/recordings on endangered media; documents that are part of an obsolete or commercially unsupported system; documents in regular demand.
It is clear that the definition of the criteria for selection is an arbitrary choice and a mandatory one, the responsibility of which belongs to the stakeholders, that is, the archival institutions. Generally, the authors' preference is a trade-off between the IFLA and the IASA positions: documents in immediate risk/recordings on endangered media; demand: priority is given to materials in constant demand; documents that are part of an obsolete or commercially unsupported system.
Once the preservation schedule is planned, the remediation process can start.
The first thing to do when an audio document enters the remediation process is to document its physical condition, in order to know what was its state before any restoration was performed (step (1.1)). The photographical documentation (1.1.1) includes the carrier, its housing, the cover, the case/box, and any accompanying material. At choice, some of these may be acquired by means of a scanner to enhance intelligibility (1.1.2). The photographical documentation needs to be validated by the operator ((1.1.3), in order to discard hazy or dark pictures) before moving to the next step, aimed at detecting major sign of degradation of the physical carrier (step (1.2)), such as dirt/dust deposits, mold, and tear/breaks.
Figure
Flowchart of the step 1.2 preparation of the carrier
The preparatory step terminates with the optimization of the physical carrier (step (1.4)), achieved through specific restorative actions, in order to maximize its performance condition. The purpose of the optimization is to enable the extraction of the best signal possible. This is of vital importance for carriers in a poor state of preservation that might not endure multiple playback sessions.
At this point, the carrier is physically ready for playback. However, playback requires some additional information in order to read the carrier correctly. The recording format is specific for each carrier type (step (2.1)): it can be inferred from a direct analysis of the carrier and from the writings on the cover and on the carrier itself, although often imprecise or missing. The methodology proposed in this paper provides that when the noise reduction system is unknown or it is not clear (even after a signal analysis and/or a perceptual test) whether it has been used during the recording, the carrier is played “flat,” without any compensation, and this choice is reported in the preservation copy documentation. The analysis usually requires that the carrier is tested on the reading device, which causes this operation to be particularly delicate. In the tower of Babel of the recording formats, defining the correct ones is not an easy task. Some historical research on the technologies used at the time of the recording may be required. A secondary aim of this test is to detect some symptoms/corruptions that can only be detected when the carrier is played (e.g., sticky shed syndrome for magnetic tapes). These symptoms still regard the physical carrier and should be treated accordingly before proceeding with the signal extraction.
The definition of the recording format may have involved multiple replay devices: when the format is clear, the best equipment should be (1) selected and (2) adjusted for signal extraction (2.2.1). The same applies to the analog/digital converter and the rest of the remediation chain down to the workstation that acquires the data (2.2.2). Some differences may be observed in the procedure depending on the type of carrier, due to the mechanical-chemical-electrical specificities. The methodology presented in this paper aims at being general; however detailing the procedure for each type of carrier goes beyond the scope of this work. At a macroscopic level, a partition can be done between carriers with analog or digital signals. The main differences regarding these two groups are that carriers with digital signals do not require a link of the remediation chain that is fundamental for carriers with analog signals, the analog/digital converter; that some types of carriers with digital signals are the only exception to monitoring (e.g., CD, audio files, etc.); that algorithms for automatic error detection/correction can be used during the digital-to-digital copy.
An important feature of the methodology proposed by the authors is that automatic rerecordings with simultaneous use of several systems is impossible, because the protocol requires that each re-recording is monitored by an operator (step (2.3)). Every audio document is inherently unstable and requires the annotation and the description of a number of signal alterations; let alone the supervision of the remediation chain (a malfunctioning device can tear, break, or crumple the carrier; a reason why an operator must always be ready to intervene). Here is a list of the alterations that can be noted during playback: local noise: clicks, pops, signal dropout due to joints, or tape degradation; global noise: hums, background noise, or distortion (periodical or nonperiodical); alterations produced when the sound was being recorded: electrical noises (clicks, ripples), microphone distortions, blows on the microphone, or induction noise; signal degradation due to malfunctions of the recording system (i.e., partial tracks deletion).
When the signal extraction is complete, a set of manual and of automatic controls should be applied to the digital waveform (step (2.4)). If the resulting audio file is well formed and compliant with the desired parameters, it can be exported in the format selected for the preservation action (see Section
Audio metadata are of paramount importance in the documentation of the preservation copy (step (3.1)). Some of them are known
This subsection provides detailed information on the aforementioned preservation copy, which is a key element in the methodology developed by the authors. A preservation copy (or archive copy) is “the artifact designated to be stored and maintained as the preservation master. [
Restoration, when referred to a preservation copy, is only allowed if it is intended to optimize the physical condition of the carrier before signal extraction. In the authors' view, only the intentional alterations should be compensated at a preservation copy level (e.g., correct equalization of the re-recording system and decoding of any possible intentional signal processing interventions). As has been said in Section
During the remediation process, every part of the physical original document—multimedia in itself, because it consists of audio, images (label, case, carrier corruptions, etc.), text (accompanying material), and smell (mould, vinegar odor, etc.)—is converted into a digital file, which results in a Unimedia document: a fusion of different media in a single flow of bits [
Logical representation of the elements contained in a preservation copy.
In a preservation copy, a distinction is made between
The audio signal should be stored in the preservation copy using the Broadcast Wave Format, sampled at least at 96 kHz with a 24-bit resolution (for digital source documents, such as Compact Discs and Digital Audio Tapes, the sampling frequency and resolution of the preservation copy can equal the original). It is advisable to use the monophonic format, where each recording track is equivalent to a different file with Pulse Code Modulation representation [
These guidelines follow the precept that “the worse the signal, the higher the resolution”, attributed to George Brock-Nannestad during a personal communication to the authors in October 2007. The statement by Brock-Nannestad is based on the fact that the characterization of the documents with a low-quality useful signal usually relies on its corruptions, which are generally spread on a broad band. Therefore a high resolution is needed in order to capture as much information about the corruptions.
The information reported on edition containers, labels, and other attachments should be stored with the preservation copy as a static image, as well as clearly visible carrier corruptions (two examples are given in Figure
(a) Example of one of the set of images included in the preservation copy of a compact cassette. Each element should be clearly visible in all its details, so usually a preservation copy contains from four to eight images. It is recommended that at least one includes the carrier with all its accompanying material—especially if these are not listed somewhere else in the textual documentation. Below the document's signature, a small ruler can be observed: according to the recommendation of the Italian Ministry of Cultural Heritage [
A video of the carrier during playback—synchronized with the audio signal—ensures the preservation of eventual information on the carrier, especially open-reel tapes (physical conditions, presence of intentional alterations, corruptions, graphical signs). The video recording offers the following. Information related to magnetic tape assembly operations and corruptions of the carrier (disc, cylinder, or tape), which are indispensable to distinguish the intentional from the unintentional alterations during the restoration process [ A description of the irregularities in the playback speed of analogue recordings (such as wow and flutter, which are audio distortions perceived as an undesired frequency modulation in the range of [ Instructions for the performance of the piece (in particular in the electroacoustic music for tape): from the video analysis, some prints of the tape can be displayed; they represent either the synchronization of the score or the indication of particular sound events.
The video file should be stored with the preservation copy. The selected resolution and the compression factor must at least allow to locate the signs and corruptions of the carrier. In the authors' experience, a
A preservation copy is meant to be self-explicated. It should provide all the information needed to access, read, and interpret correctly its content in twenty or a hundred years from now. Apart from the technical specifications of the file formats, this aim is achieved with the inclusion of a descriptive sheet, which proves useful also in case the logical structure of the archive is modified and some documents get misplaced. A descriptive sheet is divided in four sections: a complete list of the elements included and their relative path; description of the preservation copy (general info and audio metadata for each audio file); description of the source document (provenance, recording format, etc.); description of the video recording, if present.
It is widely accepted that, for both technical and economic reasons, the preservation of audio documents relies upon transfer to, and storage in, the digital domain. However, digital files and carriers are not immune from format obsolescence and physical degradation. Quite the opposite, the pace at which technology advances makes each new “generation” shorter, and a minor physical corruption can make all the information inaccessible (unlike analogue carriers, where a scratch on the surface of a phonographic disc does not prevent the access to other parts of it). In this sense, digital files and carriers show weaknesses that are even more dangerous than the analogue ones, because “digital information can be lost—without warning—at any time” [
According to the preservation best practices expressed in [
The software system presented in this section consists of a set of tools that support the remediation process. It is open source (GNU GPL v.3) and it includes two Java applications with a graphic user interface (GUI) and a number of shell scripts and Java programs without GUI. All of these elements are integrated in the preservation workflow schematized in Figure
High-level schematization of the preservation workflow from the viewpoint of the software tools.
In function of the role played in the workflow, the software tools described in the next subsections can be grouped in the following: tools for the active preservation of audio documents; tools for the description of the contents (cataloguing); tools for data monitoring and maintenance; tools for data sharing.
The block on the top left in Figure
As a consequence, additional steps are needed in order to obtain an archive of catalogued audio resources ready to be accessed by the general public, starting from the archive of preservation copies. The main difference between the two stages is the description of the content, which is missing in the preservation copies. The preservation copies are only intended to safeguard the audio document as such, without any relation to its content (symphonies, interview, electroacoustic music, or even silence). But the final users need to search the documents with keywords related to the content (title, author, subject, etc.). For this task, solid competences on the content of the recordings are required; in this sense, this represents a variable part of the preservation process, because unlike the first part, which applies to all types archives, this one depends on the area of interest of the recordings: it may be formed by musicologists, anthropologists, linguists, historians, and so on. In this paper, a scenario with linguists is considered, that is, a sound archive of speech documents. Going back to the workflow, the cataloguing staff need to access the audio contained in the preservation copies, which is cumbersome and difficult to share over a network connection (a stereo audio file with a duration of 48 minutes, a sampling frequency of 96 kHz, and a resolution of 24 bit occupies
Regardless of the type of the recordings, the relation between the original document, the preservation copy, and the access copy is 1 : 1. This is not true for the relation between the preservation/access copy and the audio resources for public fruition, which are abstract entities independent from the structure of the physical originals. They consist of audio files of varying duration, corresponding to self-concluded acoustic events such as an interview, a song, and an intermezzo. Figure
The relation between the audio documents (in the middle) and the preservation copies (on top) is always 1 : 1. The relation between the latter and the fruition units (U1, U2, etc.) can be complex, which is often the case with archives of recordings gathered on the field for linguistics and ethnomusicological studies.
It is to be noted that almost every step of the process can be assisted or automatized by software tools, except for the reorganization of the audio material, represented by the pink rectangle in the middle of Figure
From the viewpoint of their function, the software tools can be divided to the following. Working tools Archive alignment (working local archive, mid-/long-term archive on the remote server, backups) Creation and sharing of access copies Database Programs for data ingestion into the database Control tools Process monitoring Data verification (mid-/long-term) Backup procedures (database, archives) Monitoring of the data growth.
Preservation Software Kit (PSKit) PreservationPanel is an open-source software application developed in Java by the authors and licensed with the GNU GPL v.3. It counts almost 50,000 lines of code and it has been used since 2011 in the laboratory for audio preservation of the Scuola Normale Superiore di Pisa (see Section
At a user level, the main functions of PSKit PreservationPanel are the creation and the maintenance of the archive of preservation copies; data ingestion into the database (see Section
The usefulness of PSKit PreservationPanel is mainly represented by the quality control that it performs on the remediation process, managing data and metadata in parallel and thus ensuring a constant alignment between them. It significantly reduces the processing timing, by batch processing some categories of files, and at the same time eases the workload of the operator, by hiding all information that is known
The panel for the description of single documents (physical original, recording format, and preservation copy) is customized for each carrier type. Filters are applied to attributes, that may apply or not to the selected carrier type, resulting in different components on the interface. The introduction of errors is minimized by loading in the components only the valid values for each applicable attribute. For audio-specific metadata extraction (panel for batch processing), the authors have implemented in their system a modular tool for analysis and validation of digital objects in (digital) preservation programs developed by JSTOR and Harvard University [
Metadata associated to the audio files in the descriptive sheet of a preservation copy. Items marked with a star (*) are not obtained with JHove: the name of the file is given by the user, and the duration of the file is calculated with PSKit PreservationPanel (class MetadatiAudio, private method durataTraccia(File f) that returns a String with the duration in the format HH:MM:SS).
Metadata | Description |
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Name* | Name of the audio file contained in the preservation copy including the extension, and without any leading directory components. |
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Duration* | Duration of the audio file in the format HH:MM:SS. |
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Size | Size of the audio file in a human readable format, for example 874 MB or 1.2 GB. |
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Extension | Extension of the audio file, for example, wav. |
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Format (MIME type) | The standard recognized name for the format of the audio object. |
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Encoding | The encoding scheme used when audio digitization occurred for the described audio object. The majority of digital audio recordings will have a value of “PCM”. |
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Profile | String obtained with the combination of the values Format and Audio Format extracted from the header of the audio file. For example, PCMWAVEFORMAT. See the WAVE file format specifications for details. |
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Number of tracks | Tracks are here intended as channels; therefore a monorecording will have 1 track. This definition has been adopted to resolve the ambiguity of terminology between “track” (here intended as autonomous audio file, e.g., a CD has 14 tracks) and “channel” (typical values would be 1, 2, 4, and 8). Note that the metadata “Signal type” (mono, stereo, …) is not listed in this table because it is a qualitative evaluation of the operator and it cannot be extracted automatically—nevertheless it is included in the descriptive sheet in the section that describes the physical original. In the authors’ experience, “number of tracks,” “number of channels,” and “signal type” are the minimum combination of metadata to describe any type of recording format with no ambiguity whatsoever. |
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Bitdepth | The number of bits per sample for the audio content of the described audio object. This element describes the actual number of bits of the sample, whereas Word Size describes the number of bytes used to contain the sample. |
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Sample rate | The sample rate of the audio data for the described audio object. |
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Byte order | The order in which a sequence of bytes are stored in computer memory. Used to indicate whether the file is in little-endian or big-endian order. |
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First sample offset | The byte offset of the start of the data chunk which actually contains the waveform data with respect to the beginning of the file. |
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Compression | Name of the algorithm for data compression applied to the audio file, if any. For preservation copies, it should always be “none.” |
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Checksum MD5 | A string indicating the checksum signature of the audio object. For example, 8847e21949079bfd4bf0c2bc26ba074a |
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Checksum CRC32 | A string indicating the checksum signature of the audio object. For example, 422f2901 |
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Checksum SHA-1 | A string indicating the checksum signature of the audio object. For example, 10a000e21a4c99479b15b852fcb3467b51c08cf5 |
Other operations supported by PSKit PreservationPanel in the panel for batch processing are (a) assignment of audio and contextual information files from default temporary folders to the correct preservation copies; (b) creation of an XML file with the checksums of the audio files for each preservation copy; (c) creation of descriptive sheet; (d) validation; and (e) transfer to remote server. Figure
Abstract view of the activities that take place in the preservation laboratory.
This subection describes the procedures that take place on the server machine to which the complete preservation copies have been transferred using PSKit PreservationPanel. All of the procedures are automatically executed on a daily-weekly-monthly-yearly basis according to the Daily schedule Creation of access copies Sharing of access copies on a web page with limited access Automatic mail messages to notify the new available audio files Calculation of the total duration of the digitized audio Backup of the audio archive Backup of the database Weekly schedule Backup of the website Grouping of daily database backups in compressed archives Monthly schedule Monitoring the new items added to controlled vocabularies in the database Grouping of weekly database backups in compressed archives Yearly schedule Grouping of monthly database backups in compressed archives Other services Periodical messages reporting the status of the server machine Possibility to monitor single processes with periodical reports sent via mail.
The creation of access copies (item number (1) in the previous list) involves a shell script that downsamples the audio in the preservation copies and converts it to a compressed format, adding new metadata to the header. The compressed files are then associated to the photographic documentation, and the resulting object is moved to the archive of access copies. This archive is accessible through a web site with restricted access (item number (1) in the previous list). Finally, every morning a script checks if on the previous day there have been new uploaded preservation/access copies and, if so, sends a notification mail message with the list of the audio files and link to retrieve them. This way, each member of the cataloguing staff is updated on a daily basis and can access the new documents very quickly, enabling a fast processing chain from active preservation to the archive of preservation copies and to the archive for access.
The system as it has been described in this work uses a redundant Hard Disk Drive array to store the data (archive of preservation copies, access copies, database, etc.) in the long term. The specific problems related to the checking, refreshing, and migration technology fall within the scope of the research area of digital preservation (see, e.g., [
The tool that the members of the cataloguing staff use to populate the database is called PSKit CataloguingPanel and like PSKit PreservationPanel has been developed in Java during the collaboration with the sound archive of the Scuola Normale Superiore di Pisa (see Section
Once the audio material has been reorganized and new audio files coinciding with self-concluded acoustic events have been created, the cataloguing staff can proceed with its classification and its description. PSKit CataloguingPanel is essentially an interface for data ingestion, but just like PSKit PreservationPanel it follows an attentive study of the requirements carried out in tight collaboration with the linguistics research team. Long discussions have been made to refine the data model, trying to bridge the gab between two disciplines such as computer science and linguistics: an extended time spent for the collection of the requirements has paid off with the realization of a tool that guides the operator in the workflow making it fast and simple and at the same time ensures data consistency and minimizes the introduction of errors.
PSKit CataloguingPanel allows to maintain the connection between the new self-concluded audio files coinciding with the catalogued acoustic events, and the source files in the preservation copies that have been used to created them. This connection is crucial because it is the only link between the archive for preservation and the archive for access, that is, between the preservation metadata and the content descriptions. More details about this relation are provided in the next section.
A database that is designed within the scope of a preservation project must be able to maintain the data, as well as the relation between the data, that belong to two different and opposite aspects of the process: the active preservation of audio documents on the one hand and the cataloguing of the contents on the other. These aspects are opposite because the first focuses on the document as such, regardless of their content. The metadata produced in this part of the process are mainly technical and audio specific. The second aspect sacrifices the fidelity to the data structure of the physical original carrier in favor of abstract self-concluded acoustic events that coincide with culturally mediated interpretations of the audio stream. The metadata produced in this part of the process are content dependent and vary according to the area of interest of the recordings. For example, in the scenario with speech documents of dialectological relevance, the metadata will include the linguistic area, the date of creation and the people involved in the conversation, the topics of the conversation, and an abstract of what is being said, in order to provide the final users with as much information as possible.
The database adopted by the software system described in this paper was created using the relational model, with Oracle MySQL. Its population is performed by means of the applications described in Sections
The operational protocol presented in this paper has been developed in several research projects to which the authors have participated since 1996: “Electronic Storage and Preservation of Artistic and Documentary Audio Heritage (speech and music)” funded by the National Research Council of Italy (CNR); “Preservation and Online Access of Contemporary Music Italian Archive” funded by the Italian Ministry for Scientific Research; “Preservation and Online Fruition of the Audio Documents from the European Archives of Ethnic Music” funded by the EU under the Program Culture2000; “Search in Audio-Visual Content Using Peer-to-Peer Information Retrieval” funded by the EU under the Sixth Framework Programme.
Important European archival institutions have been involved, including “Speech and Music Archives” of the National Research Council of Italy “Archive of the Studio di Fonologia Musicale,” owned by the Italian National Broadcast Television; “Luigi Nono Archive”; “Bruno Maderna Archive;” and “Historical Archive of Contemporary Arts” of the Venice Biennial.
In particular, the protocol has been perfected during two research projects presented in the next paragraphs.
In 2009, the audiovisual archive of the Fondazione Arena di Verona and the Department of Computer Science of the University of Verona started a collaboration finalized at the digitization of the sound collection owned by Arena. The joint project lasted two years and accomplished the following goals: definition of a methodology for preservation, after a survey on the state of preservation of the archive and of its peculiarities (number and type of documents, genre of the recordings, objectives of the digitization, etc.); definition of an operational protocol for the remediation of the audio documents and for the management of the laboratory (maintenance routines for technical equipment, rules for the documents handling and storage during treatment, etc.); realization of a laboratory, inside the archive, fully equipped to support the active preservation of audio documents (Figure knowledge transfer to the archive personnel (on a methodological level, and on an applied level: use of the technical equipment, use of the original software tools developed on purpose during the project, physical restoration of the audio carriers, etc.); creation of over 1,200 preservation copies of different types of audio documents (magnetic tapes, optical discs, and digital nonaudio carriers).
Laboratory for the preservation and the restoration of audio documents inside the audiovisual archive of the Fondazione Arena di Verona. On the right, a large collection of recording/replay devices can be observed on the shelves. On the left, an open-reel recorder Studer A812. On the desk, an A/D-D/A Converter PRISM ADA-8XR and two Compact Cassette recorders.
Panel for the description of single documents in PSKit PreservationPanel for the carrier type “phonographic disc.”
The archive comprises tens of thousands of audio documents stored on different carriers (from wax cylinders to digital carriers), nearly a hundred pieces of equipment for replay and for recording (from wire to magnetic tape recorders and phonographs) and bibliographic publications (including monographs and all issues of more than sixty music journals from the 1940s to 1999). The audio archive is divided in a historical section, containing the live recordings of the operas staged every year at the Arena during the summer season, and the Mario Vicentini section, named after its donor and the estimated value of which is 2,300,000 Euros. The archive is being enriched every year with the recordings of the new opera seasons, now memorized on digital data storage devices.
Most recordings consist in live performances of classical operas staged in an open-air setting, the Arena di Verona. On the average, the audio documents presented a good state of preservation, except for some among the oldest open-reel tapes (late 1960s and early 1970s), a lot of Compact Cassettes from 1981 to 1983, and Compact Discs from the early 2000s which proved unreadable. The precision incubator commonly used for the thermic treatment of tapes with specific syndromes [
Audio recordings play an important role in the field of linguistics: from life stories to dialect investigations, they provide researchers with invaluable first hand material. Unfortunately first hand does not mean being unchanged with respect to the original acoustic source: capturing an acoustic event is never a neutral operation, as explained in Section applying the methodology for preservation to the audio documents of the area of linguistics, after a study of their characteristics (most problems are related to the fact that the recordings have been gathered on the field, often in inadequate conditions, with nonprofessional equipment and inexpensive carriers, etc.); realizing a restoration laboratory, inside the laboratory of linguistics, fully equipped to support the active preservation of audio documents; transferring knowledge to the technical staff of laboratory of linguistics to enable autonomy after the end of the project (on a methodological level and on an applied level: use of the equipment, use of the original software tools developed on purpose during the project, physical restoration of the audio carriers, etc.); creating an archive of preservation copies of different types of audio documents (open-reel tapes, Compact Cassettes, Digital Audio Tapes, and digital nonaudio carriers).
Even if the importance of audio documents is acknowledged in the community of linguistics, this project has been the first ever on the Italian territory to introduce the competences of preservation into a laboratory of linguistics. For over a year, the authors have worked inside the laboratory in tight connection with the linguistics research team, in a proactive multidisciplinary attitude, bridging the gap between the disciplines' approaches and vocabularies. As a result, the original software system described in Section
A major question that had to be solved is related to item number (4) in the previous list of objectives: the laboratory of linguistics holds its own collection of audio recordings, but the research project had the ambition of censusing and collecting as many external public and private archives as possible on the territories where the Tuscan language (
From the viewpoint of the scientific research, the original software tools that constitute the system presented in this paper belong to the area of cultural interfaces. They are characterized by a development that has been conducted with a transdisciplinary approach, achieved by means of a tight and prolonged collaboration of the researchers in computer science and engineering with the experts of different scientific disciplines (musicologists, linguists, archivists, etc.). This collaboration created the conditions for many opportunities of mutual confrontation and for a better modeling of the requirements, for a deeper understanding of the others' terminology, methodology, and so forth. This approach was mainly reflected by the design of the database (reconciliation of different approaches to preservation, information modeling); the formalization of the workflow (accordance between the theory of preservation and laboratory practice): sustainability and processing timing, assistance to remediation sessions, and cataloguing on parallel workstations.
Besides improving the quality of the laboratory work, the results obtained prove that the introduction of original software tools in the process of active preservation of audio documents opens the way for an effective answer to the methodological questions of reliability with relation to the recordings as documentary sources, also clarifying the concept of “faithfulness” to the original and situating it in the precise limitations of the audio equipment technology.
The architecture of the software system reflects the founding principles of the methodology applied to the active preservation audio documents. Assuming that those principles are agreed upon and respected, the system can be adapted to the needs of other archives at low cost—a desirable objective that would help correct preservation practices to spread, encouraged by the use of adequate and freely shared tools.
The authors have no conflict of interests to declare in relation with the software system described in this work.