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Digital audio visual restoration
 

Digital audio visual restoration

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One day hands on workshop

One day hands on workshop

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  • good morning
  • 500 mailing list members JISC Digital Media (formally TASI) is a JISC funded service, offering advice and guidance to FE and HE and the cultural heritage sector on all matters relating to the creation, use and management of digital media for learning, teaching and research. We do this via: Website Helpdesk Hands-on training Mailing list, blog and twitter Consultancy
  • Digital information is exactly the same form for all digital files; word docs, video files, spreadsheets etc etc
  • Sampling theorem states that for accurate recording a sampling frequency of twice the bandwidth is needed Range of tape machines approx 20-Hz – 20Hz
  • Bit depth determines dynamic range DR is the available values of volume
  • Explain PCM Audio and how it’s contained in a wrapper
  • Digital video files NOTE: we intentionally say ‘file’ rather than tape or DVD because, unlike the case with analogue media, the information and the medium have become distinct from, the carrier in the digital domain a digital file can be stored on a DVD, a CD, a tape, a hard drive, a Flash memory card, etc. the first commercial digital video recording equipment came out in 1986 computer-based digital video followed in around 1990 now there are thousands of different formats digital video was central to the advent of ‘web 2.0’ applications by simplifying the dissemination of moving images on the Internet
  • How does a digital video file work? as with film and analogue video, a moving image is simply a sequence of still images. In the case of PAL video there are 25 images per second unlike film, but the same as analogue video, each image is broken down into horizontal lines, 576 in the case of PAL. here is where it differs from analogue video. First of all, each horizontal line is broken down into dots (720 in the case of standard definition PAL). Information about the brightness and colour of each dot is then converted into a set of numbers. The digital file is nothing more or less than a list of all of these numbers combination of ‘wrapper format’ and ‘codec’ [add more details to facilitate next practical]
  • What is an analogue videotape? (continued) first demonstrated in 1951, but first practical system not released until 1956 first format suitable for domestic use not available until the 70s most common formats: Quadruplex (2” tape) Type B (1” tape), EIAJ-1 (1/2” tape), U-matic, MII, Betacam, Betacam SP, Betamax, VHS, S-VHS, VHS-C, Video8, Hi8 don’t confuse tape format with technical standard, i.e. NTSC, PAL, SECAM: these refer to the television system (factors such as frames per second, lines per frame or how colour is encoded) we use PAL – other analogue systems are not necessarily compatible, although in the digital domain PAL and SECAM can be considered to be equivalent. (In the analogue domain a SECAM video will play on a PAL machine but it will only appear in black and white.)
  • What is an analogue videotape? as with audio tape, a means of recording an electrical signal, but video, not audio NB: this is a cross-section of a tape!!! consists of a polyester ribbon which is coated on one side with magnetisable particles (originally iron oxide) in a binder which may have a lubricant as well possibly a back coating as well (backcoating is added to increase magnetic isolation between the layers of tape when on a spool and also to allow the tape to pack more evenly and under less stress on a tape reel).
  • Strengths of analogue videotape easy to record and play back (compared to film) portable, eventually culminating in the development of camcorders access: the recording and collection of moving images became something anyone could do near-universality of some tape formats (VHS, Betacam SP) reasonable image and sound quality relatively inexpensive failure is gradual and graceful: gradual because it happens bit by bit (no pun intended) and graceful because the way that it fails is easy on the eyes and ears
  • Vulnerabilities of analogue videotape fragile: can be damaged by badly adjusted or dirty playback mechanisms prone to deterioration: even if stored perfectly the signal will fade over time compared to digital NLEs, the creative capabilities of editing are very limited editing requires creation of a new (inferior) copy relatively expensive to edit copying inevitably results in a reduction in quality the original image and audio quality can be much lower than that provided by digital formats become obsolete, some quite quickly now mostly obsolete
  • Common reasons for signal deterioration age: regardless of how the tape is stored, the signal will eventually fade temperature:heat damages and can actually erase the signal poor recording techniques overuse (playing a tape, digital or analogue, causes wear) playback head not regularly demagnetised – the magnetic fields of the tapes will magnetise the recording head as they pass over it – the head then magnetises tapes as they are played, slightly erasing the signal print through: left on a reel for long periods of time, a given section of tape may magnetise the parts of the tape adjacent to it on the reel. Most obvious in audio recordings as a very faint echo either before or after sound rough handling of tapes: a sharp jolt will cause a tiny realignment in the particles on the tape resulting in a small but significant signal loss
  • Quality assurance 1 what can go wrong when we convert analogue video to digital video? e ven if the source material and the target medium are extremely high quality it is still possible to end up with inferior results if the actual digitisation process is not carried out as well as possible s everal steps should be taken to avoid this pitfall first and foremost is to ensure that your equipment is cleaned and calibrated regularly.
  • Quality assurance 1 cleaning the playback head of your videotape deck not only improves the signal being sent to the digitisation device but also decreases the chance of the deck damaging the source videotapes. the heads should also be ‘cleaned’ by regularly demagnetising them, again both to improve the signal and to avoid damaging the source material note that cleaning and calibration of your equipment does not have to be a complex process f urthermore, it is something that can (and should) be done daily and so cannot be left to be covered by a service contract calibration involves playing back a video cassette with known colour and contrast values these values can then be measured and any discrepancy located and addressed
  • Common physical problems sticky shed syndrome: the binder on polyester tapes absorbs water, which breaks down the long-chain molecules in it, making it sticky. It can scrape on the head, stick to the head and actually flake off the tape, not only damaging the recording but also clogging the heads on the machine. The most common treatment is to bake the tapes on an oven at around 60 degrees Centigrade, after which they should be playable for a few weeks. Other suggested treatments include cleaning with alcohol to take the water out of the tapes. backcoat shedding: not to be confused with sticky-shed. The backcoat on tapes can become detached and clog up the heads on the machine. mechanical damage caused by poorly maintained decks: frayed edges, creases, stretching, even breaks. mould: eats into the binder of the tape and can clog playback heads. Most importantly, it can spread: it’s a live thing. It’s essential that any tape with mould be removed from the vicinity of other tapes immediately . It’s also important to wash your hands after handling such a tape to avoid spreading the mould. vinegar syndrome:older tapes were made with an acetate base which over the years can begin to break down and produce vinegar. The tape itself can shrink or become brittle. There is no treatment for this. The only thing to do is to copy the tape to a new medium as soon as possible. Were the first videotapes made with acetate or was polyester in use by that time?
  • Objectives: Students are shown how to clean heads using cotton buds and isopropyl. They are then given VHS cleaning cassettes and instructed to clean the heads. Student prepare their workstations for capture. Playback is monitored & colour bars are captured and digitised. Digitisation is ended, playback is ended. Colour bars are then checked with vectorscope and waveform analyser for accuracy Captured files are briefly error checked (using methodology from exercise 4) then deleted Be Sure To Say: some things cannot be corrected let alcohol dry before inserting a tape! Materials: VHS deck with removable cover Cotton buds and isopropyl VHS cleaning cassettes Correctly balanced colour bars on VHS cassettes Software vectorscope Software waveform analyser Capture software Windows Explorer GSpot JHOVE
  • Objectives: Students are shown how to clean heads using cotton buds and isopropyl. They are then given VHS cleaning cassettes and instructed to clean the heads. Student prepare their workstations for capture. Playback is monitored & colour bars are captured and digitised. Digitisation is ended, playback is ended. Colour bars are then checked with vectorscope and waveform analyser for accuracy Captured files are briefly error checked (using methodology from exercise 4) then deleted Be Sure To Say: some things cannot be corrected let alcohol dry before inserting a tape! Materials: VHS deck with removable cover Cotton buds and isopropyl VHS cleaning cassettes Correctly balanced colour bars on VHS cassettes Software vectorscope Software waveform analyser Capture software Windows Explorer GSpot JHOVE
  • Objectives: Students are shown how to clean heads using cotton buds and isopropyl. They are then given VHS cleaning cassettes and instructed to clean the heads. Student prepare their workstations for capture. Playback is monitored & colour bars are captured and digitised. Digitisation is ended, playback is ended. Colour bars are then checked with vectorscope and waveform analyser for accuracy Captured files are briefly error checked (using methodology from exercise 4) then deleted Be Sure To Say: some things cannot be corrected let alcohol dry before inserting a tape! Materials: VHS deck with removable cover Cotton buds and isopropyl VHS cleaning cassettes Correctly balanced colour bars on VHS cassettes Software vectorscope Software waveform analyser Capture software Windows Explorer GSpot JHOVE
  • Objectives: Students are shown how to clean heads using cotton buds and isopropyl. They are then given VHS cleaning cassettes and instructed to clean the heads. Student prepare their workstations for capture. Playback is monitored & colour bars are captured and digitised. Digitisation is ended, playback is ended. Colour bars are then checked with vectorscope and waveform analyser for accuracy Captured files are briefly error checked (using methodology from exercise 4) then deleted Be Sure To Say: some things cannot be corrected let alcohol dry before inserting a tape! Materials: VHS deck with removable cover Cotton buds and isopropyl VHS cleaning cassettes Correctly balanced colour bars on VHS cassettes Software vectorscope Software waveform analyser Capture software Windows Explorer GSpot JHOVE
  • Conclusions as with any major undertaking, careful planning will increase the quality and reliability of your project while reducing cost and the resources needed. each step of the technical process should meet a need identified in your project specifications. It is vital to remember that digital video has a lifespan too and the transfer of analogue resources to digital should include planning for the care of the digital media in future years.
  • FAQ: what now? videocassettes are important cultural artefacts. video offers a direct reflection of our societies and contemporary history. but video is fragile and endangered, with a little training and a little effort, valuable video documents can be rescued and old dormant video collections can be reinvented and put to use. if confronted with an aging collection of tapes it is very difficult to make the situation worse: their lifespan is already severely limited, working to standards and best practice is important but not as important as doing something and doing it now.
  • Sources of further help JISC Digital Media http://www.jiscdigitalmedia.com The Digital Preservation Coalition http://www.dpconline.org/ Prestospace http://prestospace.org/

Digital audio visual restoration Digital audio visual restoration Presentation Transcript

  • Digital Audio Visual Restoration Joel Eaton & Stephen Gray
  • Housekeeping
    • Facilities
    • Fire exits
    • Lunch
    • Questions
  • Who we are
    • A JISC Advance service offering “ Still images, moving images and sound advice ”
    • Website
    • Helpdesk
    • Hands-on training and road shows
    • Mailing list, blog and Twitter
    • Consultancy
  • Discussion of group interests
  • Topics
    • What is digital restoration?
    • Why restore?
    • The implications of digital restoration
    • Restoration as part of a digitisation workflow
    • Video restoration techniques
    • Audio restoration techniques
  • What is Digital Restoration?
    • It is generally assumed that the
    • purpose of digitisation is to…
    • ‘ preserve the original intended production’
    • ‘ Intended’ by the creative producer and the technical operator
  • What is Digital Restoration?
    • Therefore restoration in this context is not
    • the improving of a recording…
    • It is restoring any errors which occurred
    • during reproduction (or digitisation) caused by:
    • Faulty or damaged media
    • Faulty playback equipment
    • Incorrect capture or playback settings
  • Being objective?
    • If we accept this interpretation of digital restoration then it is important to try and remain as objective as possible to retain the ‘intended’ work
    • Therefore today we are only concerned with restoring reproductive errors
    • More often than not, restoration is about reducing these errors as they can be impossible to remove or be hugely detrimental to the source material
  • When to re-master?
    • Re-mastered files can only be ‘fit for
    • purpose’ if you know what that purpose is supposed to be!
  • Ethics
    • What are the ethical implications of restoration?
    • Are we taking away from the original intention?
    • Do the effects of reproduction not help create the original intention? (e.g. crackles on a groove disc)
    • Are there any moral rights issues? (a: yes!)
    • Are we imposing our own subjective alterations to a work
    • How can they be addressed?
    • Acknowledgement of alterations in public domain
    • Maintaining a ‘master file’
    • Focusing on only restoring reproductive faults
  • Why perform digital restoration?
    • To attempt to accurately reproduce the original source
    • To improve accessibility to resources through a more aesthetically acceptable digital file (think of re-mastered films or albums)
    • Remember : Desirable formats will change
    • Listening & viewing trends will change
    • Therefore re-mastered files are not ‘master files’ and focus is not on long term preservation
  • Avoiding the need to restore
    • Clean
      • Media, playback equipment
    • Check
      • Capture settings, playback equipment and settings, connections, signal management
    • Calibration
      • Of playback equipment
  • How?
    • Pro-sumer AV software should offer calibration tools
    • Capture/editing software may have optional ‘plug-ins’
    • More expensive/in-depth third-party software or plug-ins available but expensive
  • Digital Audio
  • What is digital audio?
    • The representation of analogue sound waves
    • Binary data
    • Information that cannot be ‘heard’
    • From this (pic of electrical wave) to this
  • What is digital audio?
  • Digital Sampling
  • Bit depth
  • Key properties of digital audio
    • Sample rate
    • Bit depth
    • Bit rate – amount of information stored per second (kbps)
    • Channels –
      • Mono
      • Stereo: Joint, Split, Interleave
      • Quad: 4 Channels
      • Surround sound 5.1, 7.1
      • Multi-track recordings (also common in larger tape formats)
  • Key properties of digital audio
    • Wrapper formats – Containers of audio data and metadata. May be able to store video data as well
    • CODECs – (COmperssor DECompressors) are used to encode audio data, often compressing the information to create smaller file sizes and use less bandwidth or disk space
    • Digital Audio Restoration Techniques
  • Volume Correction
    • Causes
      • Too much input gain
      • Too little input gain
    • Problems
      • Distortion
      • Quiet signal which results in greater noise when volume is increased in post
    • Other issues
      • Noise from playback media/equipment may have helped determine an incorrect input gain level
      • Incorrect amplification of signal
  • Volume Correction
    • Diagram of quiet signal and explain why noise is introduced
    • Diagram of distorted signal and explain how distortion occurs, I.e sq wave etc
  • Volume Correction
    • Solutions
    • Normalisation – what it does and why it’s bad. Use a denoiser as well?
    • De-clipper – what it does… intelligently tries to repair clipping of waves
  • Removing/reducing noise
    • Causes
      • Noise from media,
      • Recording chain,
      • equipment
    • Problems
      • Incoherent signal results in poor listening experience
    • Other issues
  • De-noise
    • Noise is often made up from bands of frequencies instead of just one or two.
    • When mixed with a signal it is difficult (sometimes impossible) to remove noise in the same freq bands
    • Show EQ Hum graph
  • De-noise
    • A de-noiser analyses the constant frequencies in a signal and reduce these
    • Can leave audible artifacts
    • Often ‘trial and error’ approach with regards to setting threshold
    • Some systems can analyse a small section of noise and apply removal to entire signal
  • De-noise
    • Before and after waveforms and audio files
    • Screen shot of GUI and explain
  • De- hiss
    • Tape hiss exists in some magnitude on all tapes.
    • Prevalent in specific narrow frequency bands
    • Can be analysed in a similar way as a de-noiser works
    • Audio files
  • Removing specific noise and transients
    • Common effects of faulty equipment and worn media are crackle and pops (vinyl), and hiss
    • De-crackler/de-clicker process commonly uses an algorithm which looks ahead in waveform and analyses impulses which could be caused by crackling. It decides whether these are crackles or part of the signal and removes them accordingly
    • Audio files
    • Screenshot of GUI and explain
  • Speed correction
    • The result of incorrect playback speed during digitisation
    • Sometimes exact speed may not be known
    • Element of guesswork can be undertaken
      • This can be easier with spoken work than music
  • Digital video
  • Key properties of digital video
    • Are digital files , not digital tapes, DVD discs, etc.
    • Can be housed on a wide variety of media types (hard drives, tapes, solid state devices etc.)
    • Became common in 1990s
    • Thousands of different formats exists
    • Has helped fuel ‘web 2.0’ concept of sharing digital information, via the Internet
  • How does it work?
  • Key properties of digital video
    • Frame rate: images per second
    • Frame size: vertical / horizontal
    • Aspect ratio: relative dimensions such as 4:3 or 16:9
    • Bit rate: data per second required for playback
  • Key properties of digital video
    • Bit depth: number of colours used to describe each colour channel of an image
      • i.e. ‘8bit’ =
      • 8 bits to describe red
      • 8 bits to describe green
      • 8 bits to describe blue
      • = over 16 million possible colours!
  • Key properties of digital video: Wrappers and CODECs (same as for audio!)
    • Wrappers: container, holds video, audio and metadata etc. together
    • CODECs (Compressor DECompressors) are used to encode the video and save resources such as bandwidth or disc space
  • Key properties of digital video: CODECS
      • Can be uncompressed : no true CODEC used
      • Can be lossless: no loss of information, done through mathematical shortcuts
      • Or lossy: ‘ approximations’ used, either within each frame (interframe) or between frames (intraframe) or both
  • Say hello to the analogue video tape!
  • What is an analogue videotape?
    • Became common in 1960s
    • Used to record image and audio from a camera, then off-air
    • There are hundreds of different formats
    • Common formats: VHS, Betamax, U-matic
  • What is an analogue videotape?
    • Tape structure: Cross section
  • Analogue videotapes
    • Strengths
    • Very easy playback
    • Cassettes made innovative new camcorders possible
    • Made personal video archives possible
    • Some tape formats were almost universal
    • Image and audio quality OK for original uses
    • Often inexpensive
    • Failure is ‘gradual and graceful’
  • Analogue videotapes
    • Vulnerabilities
    • Liable to slow but inevitable demagnetisation
    • Limited editing and creative capabilities
    • Relatively expensive to edit
    • Editing / copying inevitably results in degradation
    • Image and audio quality can be inferior to digital
    • Some formats were short-lived
    • Now mostly obsolete, replaced by digital
    • Fragile:
  • Causes of problems
    • Age (gradual signal loss)
    • Temperature & humidity
    • Poor recording technique
    • Playback head not demagnetised
    • Rough handling
    • Playback
  • Avoid restoration: calibrate!
  • Cleaning and calibration
    • Risk
    • Image and audio quality could be compromised during digitisation
    • Measure
    • Clean and calibrate equipment routinely
  • Tracking error
  • Cleaning and calibration
    • Cleaning and calibrating not necessarily scary or complex procedures!
    • Daily procedures cannot be left to service contract
    • Calibration involves playing back a video cassette with known values
  • Demonstration: cleaning a deck
  • Videotape problems
    • Sticky shed syndrome: binder absorbs water, becomes sticky then detaches
    • Print through
    • Backcoat becomes detached and clogs playback heads
    • Mechanical damage from playback
    • Mould
    • Vinegar syndrome: early tapes had acetate base
    • Inevitable signal loss (results in colour problems)
    • Digital Video Restoration Techniques
  • Exercise:
    • Checking video using ‘scopes’
  • Exercise:
    • Colour correction
  • Exercise:
    • Sharpening & levels
  • Exercise:
    • Extension exercise
  • Restoration in the digitisation workflow
    • Information needed for metadata (Take notes whilst working!)
    • Batch process or individually? Dependent on:
        • Value of resource
        • Time available
        • Quality required
  • Delivery platforms
    • The rendered re-mastered file will need to be encoded to a format defined by your intended means of delivery
    • Physical media or online?
    • Compression?
      • Lossy or lossless
      • Fidelity vs. accessibility
  • Delivery platforms
    • Many platforms do not permit hi-resolution delivery
    • Therefore don’t spend time making improvements no-one will ever experience!
  • Concluding remarks
    • As with all digital media projects careful planning before project begins can save valuable resources later on
    • Key question: Has the same thing been restored before by someone else?
    • Know the purpose of your media and it’s planned method of delivery before you start
    • Respect the provenance of your media and be honest about work carried out
    • Restoration is never ‘completed’ only abandoned!
  • What’s at stake if we don’t fix it?
    • New ‘digital dark age’ is a real possibility, millions of hours of analogue media become unusable everyday
    • With a little training, staff can act as valuable ‘first aiders’ and adding value to old media collections and re-invigorating the art and knwoledge of past generations
  • Sources of further help
    • JISC Digital Media
    • Advice on how to restore but also (potentially) when not to (i.e. copies are available elsewhere)
    • Prestospace
    • Consortium of technician inc. BBC addressing many restoration related problems.
    • JISC Legal
    • One stop shop for legal /rights-related advice.
  • Questions? A feedback form will be emailed soon