workshop 3 audiovisual digitisation technology

4-5 September 2012 Vietnam Film Institute Workshops 1

Practical Session: Digitisation Technology

Basics of AudioGramophone records1/4” tape

Basics of VideoSet-up for a transferSpecial problems:

stability, colour, audioBasic of FilmTelecine vs DatacineResolution, bit depthGrading (colour

correction), workflow


Audio

Gramophone records Lacquer = transcription masters Shellac = 78s Vinyl = 45s, LPs

1/4” tape = 6mm tape Many other formats, including digital: CD,

DAT, minidisc (MD), audio on videotape


Grams: What the British Library Sound Archive usesTechnics turntable, made in JapanAnd modified in USA by Kabusa


Digitising grams (records)

Batch processing Inspection Cleaning Correct playback speed Choosing the correct needle and weight Correct equalisation contour


Batch processing

The key to efficiency Organise item into groups of the same type

and condition Ideally: everything controlled through the

workflow with bar codes


Cleaning

Shellac: only pure de-ionized water and a wetting agent (eg Kodak PhotoFlo)

1 part agent to 200 parts water Vinyl: water and alcohol (industrial-grade

metholated spirits); mix 50-50 Can be done manually, or can buy

machines (Keith Monks, Nitty Gritty)


Ultrasonic bath This is a

standard bath, not made specifically for audio work

Used for very dirty objects, before final cleaning

Playback Speed

Only a problem for older shellac records, pre-1925

Speed of playback can be changed after digitisation, so just need to 'get close'

Document what you do! Also should check to ensure turntable is

operating at correct speed: strobe, tachonometer (strobe built into Technics)


Strobe Disc

Free online from vinylengine

http://www.vinylengine.com


Correct Needle and Weight

British Library Sound Archive uses one stylus for vinyl = micro groove = Shure N44-7 = “0.7 mil”

Uses three sizes for shellac: 0.0028, 0.0035 and 0.0040 inches (= “4 thou” or “4 mil” or “4.0 CT”)

In metric: 1 thou = 1 mil = 25.4 micron (= μm = micro meter) = 0.0254 mm

2.8, 3.5, 4.0 thou = 70, 90, 100μm = 0.07, 0.09, 0.1mm

The stylus will come with a recommended weight

1.5 to 3 grams for modern equipment


Correct Equalisation

Need a special pre-amplifier with adjustable equalisation for recordings made before approx 1954

BUT – frequency response can be re-shaped after digitisation if necessary

Need RIAA equalisation after 1954 So – document what you do !


Standards for Audio

Digitise at minimum of 16-bit, 44.1 kHz = CD quality (BBC uses this)

“24-bit” at 96 kHz is IASA recommendation IASA TC-04 is the standard reference for

preservation-quality audio digitisation

“Guidelines on the Production and Preservation of Digital Audio Objects” - IASA Technical Committee

Save as BWF=Broadcast Wave File= .wav + metadata


Digitisation

Needs an external sound card or equivalent – do NOT use the digitisation built into a PC (high noise => 8 bits)

British Library recommends Rosetta from Apogee http://www.apogeedigital.com

BBC recommends Sadie MANY cheaper solutions possible (notes)

http://www.apogeedigital.com/


Audio Tape

1/4” open reel, 1950s to about 2000; 1/8” cassette, late 1970's to now

Others: 8-track cartridge, multi-track pro Problems: speed, track layout, tape type More: sticky-shed, azimuth, head condition More: Dolby noise reduction systems


Open-Reel Tape Deck

Speed

Cassettes usually only one speed= 1 7/8 Open reel: 15/16, 1 7/8, 3 3/4, 7 ½, 15, 30 3 ¾ and 7 ½ common for domestic use 7 ½ and 15 common for professional use

Track layout

Usually 2 or 4 tracks, but many arrangements (depending upon head type, and mono vs stereo)

Common: Mono 2-track Stereo 2-track Stereo 4-track


Two-track:

Mono and either dual-mono or stereo

Four track: typical stereo and either stereo or dual-mono

Non-standard:


Varieties of Tape Heads

The 2 channel heads are very common; they can be used for stereo or mono.

The 4 channel can play back most anything.

Sticky-shed

Oxide comes off the backing Caused by absorption of moisture Fixed by baking: 24 hrs at 45 degrees C,

with 2 to 3 hours to heat up, and 2 to 3 hours to cool down

BBC: “we don't bake” (so use tape cleaning equipment instead)


Extreme Tape Shedding

Azimuth

If the playback head is not at the same angle as the record head, the high frequencies are reduced

Solutions: 1) every tape recorder perfect; 2) adjust azimuth on playback – and listen

to high frequencies (could use meter) Usually takes a screw driver or an Allen key

to make the adjustment

Heads

Worn – inspect and repair or replace Dirty – clean after every ½ day of use !!!

Use cotton buds and isopropyl alcohol Magnetised – demagnetise every month


Video

Much harder than audio – except for domestic formats

Presto has online training video for 2”, 1” and U-Matic http://digitalpreservation.ssl.co.uk/training/2460/2542.html

Many many possible faults in playback Use a time-base corrector, possibly a filter,

and the best colour decoder available

http://digitalpreservation.ssl.co.uk/training/2460/2542.html


Film

Threats: Vinegar Syndrome, shrinkage, damage, dust

Issues: A/B rolls, splices Wide variety of film types: reversal, B&W

vs colour, positive vs negative Master neg, interneg, print

Digitisation of Film

Telecine vs Datacine Resolution Bit Depth Digital Formats

Telecine vs Datacine

Telecine: real-time (to videotape recorder) Video output (interlaced fields) Video resolution: SD, HD Video bit depth: 8 or 10 bit max Video aspect ratios: 12:9, 16:9

Datacine: produces a file, solves ALL the above problems

Telecine excellent for access copies, but poor for preservation

Resolution

SD 704 x 576 (480 USA)

HD 1440 x 1080 = 4x3 (1920x1080 ??)

2k 2048 x 1556 = 4x3 (almost)

4k 4096 x 3112 (maybe)

From wikipedia:Standard Resolution Aspect R PixelsDigital cinema 4K 4096 × 1714 2.39:1 7,020,544Digital cinema 4K 3996 × 2160 1.85:1 8,631,360Academy 4K 3656 × 2664 1.37:1 9,739,584Full Aperture 4K 4096 × 3112 1.32:1 12,746,752


Resolution: Dutch Archive

High-level cinema (Lawrence of Arabia) fully captured at 6000 horizontal pixels (for a 65mm film)

Translates to 1470 for 16mm film Could be less for reversal stock And even less for 'telerecordings'

Bit Depth

Dutch archive uses 10-bit log scale (which is what most equipment produces)

Presto recommended at least 12 bits and preferably 14 bits, to capture the full range of film (number of “stops”)

DFT scanner will capture 14 bits Kodak: “With the advent of KODAK VISION3 Color

Negative Films, our motion picture films can capture up to 13 stops of scene content.”

For colour, it is common to ADD the number of bits in each channel, and say “24-bit colour” – but the dynamic range is 8 bits, NOT 24 !!!

Bit Depth Examples

1, 2, 4 and 8 bit illustrations:

http://en.wikipedia.org/wiki/List_of_monochrome_and_RGB_palettes


4-bit Linear vs 3-bit Log

4 bit linear = 16 steps

3 bit linear, same size steps

3 bit linear, each step twice as big

3 bit log scale, steps start small and get bigger

Digital Formats for Film

DPX uncompressed, very flexible DCI DCDM = Digital Cinema Distribution

Master: 2048x1080 (or 4096x2160) only DCP = Digital Cinema Packaging = lossy

compressed JPEG200; (not for master) JPEG2000 (lossless); 2:1 data reduction Various lossy compression formats (avoid!) And … various wrappers: MXF, AVI ...

Discussion

Who is doing digitisation? What formats? What equipment? What results? What problems?

Tea Time

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