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]
Back to topAdvantages of digital over analogue
Both analogue and digital methods have advantages and disadvantages. See Wikipedia regarding analogue recording vs digital recording for more information.
There are a few main advantages of digital over analogue methods of recording and playback:
- 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-encode.
- 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]
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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 1998. 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).
General retention and disposal authority: Administrative records covers audio 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 audio visual materials created by the organisation.
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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:
- the organisation acquires the equipment and develops the staff expertise available making it available 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]
Back to topDigital 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.
Back to topMetadata for the digitisation of analogue recordings
Metadata for records and information is structured information that describes records and information. It includes information about the object's structure, the context in which it was created and its content. Metadata is valuable in searching for, retrieving, accessing and using records and information, but it also helps to verify their authenticity and promote their long term management and preservation.
The Standard on Records Management requires that records and information are well managed. Effectively implementing metadata for records and information will assist your organisation in ensuring that its records and information are:
- reliable and trustworthy
- identifiable, retrievable and accessible for as long as they are required
- protected from unauthorised or unlawful access, destruction, loss, deletion or alteration
- kept for as long as they are needed for business, legal and accountability requirements
- systematically and accountably destroyed when legally appropriate to do so.
Some of the metadata needed to manage audio visual files may be derived from existing metadata kept about your analogue files. For example:
- a record album cover might contain information describing the recording, such as place of recording, event, speaker etc.
- 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 the preliminary stages of a digitisation project your organisation should identify requirements for metadata, both for managing the files themselves and other business purposes, 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).
| Type of metadata | Examples |
|---|---|
| Identifiers |
Title
|
|
Date
|
|
|
Unique identifier
|
|
| Creator information |
Credits (key individuals who made the work)
|
|
Personnel
|
|
| Content information |
Genre or style of recording
|
|
Content note
|
|
| Physical or technical characteristics | Quantity, e.g. audio cassette 2 of 2 |
|
Duration
|
|
|
Class of audio visual material
|
|
|
Specific type of component
|
|
|
Physical dimensions of carrier
|
|
| Gauge (for motion picture film, e.g. 8mm, 16mm) | |
|
Colour characteristics
|
|
|
Sound characteristics
|
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, 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 Records as 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 transfer requirements. Museums of History NSW should be contacted prior to transfer.
For more information about metadata for audio visual recordings see Metadata for records and information.
Back to top‘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:
- With 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]
Back to topDisposal 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.
Back to topPreservation 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’.
The International Association of Sound and Audiovisual Archives (IASA) has also developed principles regarding the digital preservation of audio visual materials. See the IASA website.
Quck 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.
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
[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
[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://dpconline.org/events/previous-events/629-decoding-the-digital-a-common-language-for-preservation
[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
Published January 2009 / Revised February 2015 / Updated November 2022 (changes to names)
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