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Digitisation of analogue audio and video (Guideline 22)

The difference between analogue and digital audio and video

Analogue recording is a linear process involving the creation of variations in a recording medium that correspond to variations in the signal being captured. Recording media used for this purpose include record albums and audio and video cassette or reel-to-reel tapes.

Analogue devices, such as VCRs, tape and record players, read analogue media by physically scanning these variations. For example, a record player creates an audio signal by translating the bumps and dips in the grooves of an album and a tape player creates an audio or video signal by reading the variations in the intensity of magnetisation of the tape.

Digital recordings are made using the binary system. Digital devices such as CD recorders and camcorders convert the signal and turn it into digital information - a sequence of numbers - sampling at set intervals. The higher the sampling rate, the more accurate the conversion is, which translates into higher quality sound or video. [1]

Advantages of digital over analogue

Both analogue and digital methods have advantages and disadvantages. See Wikipedia regarding analogue recording vs digital recording for more information.

The main advantages of digital over analogue methods of recording and playback include:

  • the binary code of digital audio and video can be read by a computer. Therefore, computers can be used to edit the data e.g. remastered to enhance sound and visual quality, and to create new effects. Analogue signals can only play what was originally recorded as it was recorded
  • digital media is non-linear (or non-real time), so it can be edited and played back starting at any point
  • digital information does not degrade and lose quality with repeated use (like tapes or record albums do). They may be copied repeatedly without loss if they are not re-encoded
  • groups of numbers can be compressed by finding patterns in them meaning the same information can be stored more efficiently.[2]

Why digitisation of analogue audio and video recordings may be required

Digitisation refers to the conversion of non-digital material to digital form. Reasons why your organisation may consider converting existing analogue recordings to digital include:

  • you face difficulties in providing access to existing resources as the devices to read them are no longer widely available in the organisation or elsewhere (for example, record players or VCRs)
  • your existing analogue resources are becoming fragile or being degraded by poor storage conditions, the passage of time or overuse, threatening their accessibility
  • you wish to improve the recordings e.g. digitally enhance them or improve indexing of the recordings and therefore search and retrieval (note: an enhanced version should not replace the original unenhanced master but can be an alternative for delivery)
  • you wish to make them more readily available by providing the potential for online delivery
  • you wish to create new versions of the recordings e.g. tailor them for other uses. [3]

For more information about the factors to consider before embarking on a digitisation project, see the JISC fact sheet, Deciding to digitise.

Prioritising digitisation of analogue audio and video recordings

All public offices have an obligation to retain accessibility to technology/equipment dependent records under s.14 of the State Records Act. This applies to all State records, regardless of how long they are required to be kept. Digitisation may sometimes be required to guarantee continued authenticity.

However, digitisation of analogue audio and video can be very resource intensive, depending on the quantities and formats involved, the equipment and software required and the quality of the original analogue source. Your organisation may, by necessity, need to take a risk based approach and establish priorities for digitisation. Priorities should include analogue recordings that:

  • are masters and are used very frequently (as analogue recordings become degraded by use. Generally copies should not be made from masters)
  • are already being degraded by high use and therefore in danger
  • have the disposal action as ‘retain in agency’ or ‘required as State archives’ in the organisation’s current retention and disposal authority (as these indicate the recordings that have significant ongoing interest to the organisation or the community).

State Records has produced a General retention and disposal authority – audio visual programs and recordings for audio, film and video programs and recordings created or commissioned by NSW public offices from c.1966 onwards. This will indicate what audio-visual records are required as State archives. The organisation’s functional retention and disposal authority may also contain additional information about disposal requirements for audiovisual materials created by the organisation.

The JISC fact sheet Selection procedures may assist you to make further selection decisions.

Managing a digitisation project

If your organisation needs to convert analogue audio or video to digital, you will need to consider very carefully whether to outsource the digitisation or to manage it internally.

Running an internal project has certain advantages including that:

  • the organisation acquires the equipment and develops the staff expertise available making it available for for future digitisation projects
  • the movement and treatment of materials can be closely supervised
  • the procurement and tendering process can be avoided, which is often expensive in its own right
  • staff time and some other overheads can be borne by the organisation rather than being an additional visible cost.

However, the advantages of using a contractor may be:

  • the organisation avoids the cost of obtaining expensive equipment and procuring expertise or training staff
  • the work can be done according to strict deadlines and it will not impact as greatly on staff time
  • the contractor can provide the necessary space.

Sometimes it is possible or preferable to outsource only part of the project. For example, the British Library outsourced the digitisation element of an audio project but managed the selection of content, digital rights management and metadata creation issues internally.[4]

Advice to assist you in making this decision is provided in the JISC factsheets, To outsource or to digitise in-house?

Appendix 2 contains a list of issues to consider if you are considering outsourcing the digitisation of audio or video.

If you are considering internally managing a project, the JISC Digital media website also has an extensive range of resources on digitisation of analogue audio and video. For example, they address budgeting for a project, project management and quality assurance. For a full list see the JISC information on cross media.

Digital audio and video file formats

The purpose of the project, requirements for video and audio quality and the length of time files need to be retained (as specified in an authorised retention and disposal authority) may need to be considered when selecting an appropriate file format. For more information see Digital audio and video file formats.

Metadata for the digitisation of analogue recordings

Recordkeeping metadata is structured information that describes a record. It includes information about the record’s structure, the context in which it was created and its content. Metadata is valuable in searching for, retrieving, accessing and using the record, but it also helps to verify its authenticity and promote its long term management and preservation.

The Standard on digital recordkeeping outlines the minimum requirements for recordkeeping metadata. Your digitised recordings must be described by this metadata. Your organisation is likely to derive some of this information from existing metadata kept about your analogue files. For example, you might have information on a record album cover describing the recording: e.g. place of recording, event, speaker etc or a reel-to-reel video might have a label showing the title, production details, date made and viewing restrictions. Additional information may be stored in the organisation’s databases or in separate data files.

As part of preliminary stages of a digitisation project your organisation should identify any additional requirements for metadata (beyond the minimum required) and draw up clear specifications. Examining existing metadata schemas for audio visual materials (e.g. METS or SMIL) [5] or those used for similar industries/projects may be of benefit.

The following table describes some metadata that may be useful to capture (where relevant and available). The second column indicates whether this is minimum required metadata specified in the Standard on digital recordkeeping.

Metadata Minimum required metadata in Standard on digital recordkeeping?
Identifier
Title e.g. program, segment, episode or interview title; e.g. title of album, title of tracks on album Yes. A repeated title field and an encoding scheme may be required to specify the type of title.
Date e.g. date of recording, broadcast, production The date of creation (recording) is minimum required metadata. A repeated date field and an encoding scheme may be required to specify the type of date.
Unique identifier e.g. item number, Barcode, unique material identifier Yes. A repeated unique identifier field and an encoding scheme may be required to specify the type of unique identifier.
Creator information Who/what created the record is minimum required metadata.
Credits e.g key individuals who made the work. In commercial productions could include producer, director, production company, producing agency Who/what created the record is minimum required metadata. An encoding scheme may be required to specify the type of individuals/organisations involved.
Personnel e.g. presenter, interviewer, interviewee Who/what created the record is minimum required metadata. An encoding scheme may be required to specify the type of personnel involved.
Content information
Genre or style of recording e.g. interview, report, live-to-air, field recording, oral history Yes. The record type is required.
Content note e.g. topics in recording, people in recording, summary Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.
Physical or technical characteristics
Quantity e.g. audio cassette 2 of 2 Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.
Duration e.g. feet of moving images or time Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.
Class of audiovisual material e.g. film reel, magnetic tape, optical disc Yes. The creating application is minimum required metadata. This would be made up of at least the medium and the file format if applicable.
Specific type of component e.g. BWF file on Hi 8 tape, original negative, digital beta Yes. The creating application is minimum required metadata. This would be made up of at least the medium and the file format if applicable.
Physical dimensions of carrier e.g. 12” Vinyl, 7” magnetic reel-to-reel tape Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.
Gauge (for motion picture film – e.g. 8mm, 6mm Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.
Colour characteristics e.g. black and white, colour Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.
Sound characteristics e.g. silent, mute, playback speed, number of tracks (e.g. 4 track audio cassette recording), encoding (Dolby, stereo, mono) [6] Not required metadata in the Standard but may be useful to capture for business purposes and to promote access.

Further metadata will be required when you convert the analogue recording to a digital format. For example, metadata will need to be captured about the digitisation process itself such as the date of digitisation and who/what undertook it (required by the Standard on digital recordkeeping), and about the old and new formats. The National Film and Sound Archive (NFSA) recommend the collection of the following minimum metadata for preservation masters:

  • Digital file recorder configuration settings
  • Digital file recorder identification; type, version, serial number
  • Details of the source tape and identifier
  • Source videotape reproducer identification; type, serial number etc
  • Master preservation file encoding details; codec type, versions etc
  • Transfer operator identification
  • Video and audio signal analysis metrics. [7]

Some metadata, particularly some technical information, can be automatically captured and embedded in some digital file formats or added later using an editor. Wherever possible your organisation should verify that any automatic metadata capture is correct and records full technical information, and not just an edited or genericised format name.

As digital audio and video are subject to rapid change, and technological obsolescence is a real threat, a review date should also be included in the metadata so that the organisation is reminded about the need to monitor its condition and useability and if refreshment or replication is needed.

If after digitisation the recordings (and/or the analogue source records) are to be sent to State archives, the organisation should also ensure that metadata such as box listings and references to supporting documentation e.g. transcripts, release forms are adequate and in line with State Records’ transfer requirements. State Records should be contacted prior to transfer.

For more information about metadata, refer to JSIC fact sheet An introduction to metadata which also contains links to more extensive information. See also State Records NSW, Managing digital records, 3. Use recordkeeping metadata for digital recordkeeping.

‘Essential characteristics’ of analogue recordings

All records have what is known as ‘essential characteristics’ (also referred to as ‘significant properties’ or ‘essence’). For digital records, essential characteristics are those properties that must be preserved over time and domains and across changing technological environments to ensure the continued authenticity, accessibility, useability and meaning. [8]

When digitising analogue audio and video or migrating digital information it is important to ensure that their essential characteristics are identified e.g. with a digital video is colour, interactivity or sound important? With digital audio, can you hear the recording in its entirety? Are breaks correctly inserted so that tracks do not overlap or run together? Testing/quality control built into the digitisation process should confirm that when digitised these essential characteristics are faithfully reproduced. With digital video, in particular, studies have shown that the essential characteristics can be reproduced in digitisation providing the right file format is chosen.[9]

Disposal of analogue source records

Source records remaining after digitisation of analogue materials have been excluded from the General retention and disposal authority – Source records that have been migrated. As yet State Records has not authorised a retention and disposal authority to cover source records from analogue to digital formats. Contact State Records if you need assistance regarding the disposal of source records.

Preservation of digital files

The preservation of the digital files does not end with their creation and the capture of metadata. Digital audio and video formats have their own preservation issues. For example, rapid obsolescence of digital technology and media instability makes digital media particularly vulnerable to loss (most have a life span of 5-10 years). Your organisation will need to monitor the files regularly to ensure they remain accessible and useable. Preservation may involve regular refreshment or regular replication to formats that can maintain their ‘essential characteristics’. The process of shifting from one digital format to another is often referred to as ‘transcoding’ . See the JISC fact sheets Transcoding digital video.

The International Association of Sound and Audiovisual Archives (IASA) have also developed principles regarding the digital preservation of audiovisual materials. See the IASA website.

Note: Click here for a full listing of the JISC Digital Media fact sheets available regarding digitisation projects.

Quick tips for digitising analogue formats

  • Treat the best version of the analogue recording as an analogue master.
  • Digitise in the highest quality format you can. Use no compression (or lossless compression if compression is unavoidable) for creating a digital preservation master. Lossy compression irretrievably reduces quality. Use open formats or formats with good ‘sustainability factors’ where possible.
  • Define your metadata requirements carefully and build metadata collection into the project.
  • Build testing into the digitisation project to ensure the ‘essential characteristics’ are maintained.
  • If enhancements are to be made, make these from a copy. Save a ‘master’ of the original and enhanced version.
  • Generate lower resolution copies for delivery (generally these will be produced from the enhanced version).
  • If possible, have another copy of the analogue master, preservation master and enhanced master stored at a different location for disaster management purposes.
  • Regularly monitor your digital masters for obsolescence or degradation.[10]

See also:

Appendix 1: Case studies of the digitisation of analogue audio and video

Appendix 2: Outsourcing the digitisation of audio or video

Digital audio and video file formats

Footnotes

[1] Sharpened.net Help Center: What is the difference between analog and digital technology? Available at: http://www.sharpened.net/helpcenter/answer.php?62

[2] How stuff works: Can you explain the basic difference between analog and digital technology? Available at: http://electronics.howstuffworks.com/question7.htm

[3] JISC Digital Media, Deciding to digitise, 14 November 2008, available at: http://www.jiscdigitalmedia.ac.uk/crossmedia/advice/deciding-to-digitise/

[4] S Tanner, Cost Reduction in Digitisation, Minerva Plus Project, Version 1, June 2006, available at: http://www.minervaeurope.org/publications/CostReductioninDigitisation_v1_0606.pdf

[5] For more information, see the metadata section of ‘Audio and Video Capture and Management’ in the National Initiative for a Networked Cultural Heritage publication, The NINCH guide to good practice in digital representation and management of cultural heritage materials Version 1. October 2002, available at: http://www.nyu.edu/its/humanities/ninchguide/VII/

[6] R Gamble and L. Curham, Chapter 17: ‘Sound recordings’ in Keeping archives, Australian Society of Archivists, Third edition, 2008 p.555-556.

[7] National Film and Sound Archive (NFSA), Digital media preservation: Video [unpublished]

[8] G.Knight, ‘Same as it ever was: significant properties and the preservation of meaning through time’ presented at Decoding the Digital: A common language for preservation, 27 July 2010,.available at: http://www.dpconline.org/events/decoding-the-digital-a-common-language-for-preservation.html

[9] M Coyne and M Stapleton, The significant properties of moving images, 26 March 2008,  available at: http://www.jisc.ac.uk/media/documents/programmes/preservation/spmovimages_report.pdf

[10] JISC Digital Media, Generic video digitisation workflow, 27 Jan 2009, available at: http://www.jiscdigitalmedia.ac.uk/movingimages/advice/generic-video-digitisation-workflow/