Legacy Media

What is Quadruplex scan?

Early VTR machines used four video heads to write and read video lines along the width of the tape from top to bottom

What is Helical scan?

Two rotating video heads writing and reading on diagonal tape tracks

In general, how do VTR machines operate?

The tape is wound from the supply spool into the VTR, makes contact with the video head drum, then the pinch roller/capstan pole, and is wound onto the take-up spool.

What is UMatic tape?

Analogue composite tape, used in the US for broadcasting

What is VHS Tape?

Domestic analogue composite tape format with no timecode, used for viewing copies

Provide examples of digital tape formats, and explain why they were used?

Sony Digibeta SP and Panasonic D5 - No generational loss or damage each time the tape is played or copied, degradation is no longer an issue

How does tape magnetism work?

An electrical signal passes through a recording head as the tape is drawn past, leaving a magnetic imprint on the tape's surface. When the recorded tape is drawn past the playback head, a signal is induced that is the equivalent of the recorded signal.

What are the issues with tape magnetism?

The magnetic layer is easily damaged, with degradation appearing with each play of the tape. They can also become demagnetised easily, via high temperatures, dust and incorrect handling

Outline how tapes should be handled?

Handle with care, check for damage, rewind the tapes and eject safely at the end of use, and return to case as soon as possible.

What is the difference between analogue and digital tape based content?

For analogue formats, there is a relationship between signal and magnetic strength, whereas for digital formats its a magnetic 1 or 0, so a more robust signal

What is sticky shed syndrome?

The tape sheds its metal oxide layer, and can clog VTR machines

Explain how VTRs use video heads?

Video heads rotate, and record or playback the picture components of electronic information, they are made up of tiny magnetic coils with a small gap between them.

How do dynamic video heads operate?

The piezo crystals receive a high voltage, move up and down to track the diagonal information for when a tape is not running at normal speed (like when jogging through on fast forward)

How does the head drum in a VTR work?

The top half of the drum rotates at the required frame rate, allowing two video heads to read or write one field per revolution. The bottom half of the drum is stationary, and guides the tape diagonally across the upper drum

Why does modulation need to occur?

Electronic processes require a much higher frequency than are contained in the signal we need for the tape, so they have to be converted to a higher frequency

How is amplitude modulation achieved?

The baseband signal is combined with a carrier signal that has a varied amplitude to produce the modulated result

How is frequency modulation achieved?

The frequency of the baseband signal is used to change the frequency slightly of the carrier, meaning it has an average frequency but changes up or down slightly based on the original baseband signal - creating a very robust signal

What is component video signal?

An analogue video signal that has been split into three component channels: Luminance, B-Y=U and R-Y=V

How is component video decoded?

A subcarrier is sent at the start of each line, which determines the chrominance signal to work out the hue of colour and the amplitude of the chroma signal determines the saturation of the colour

What is composite video signal?

An analogue video signal that combines all visual information (luminance and chrominance) into one signal

What is longitudinal/linear timecode?

The encoding of SMPTE timecode into an audio signal, which is self clocking, where if the playback changes the pitch also changes

What is BITC?

Burnt In Time Code is a readable, onscreen version of the timecode, superimposed onto footage

What is TBC?

Time Based Correction stores off tape signal in the short term memory store and then reads that memory store data out synchronised to a stable external reference, essentially stabilising the signal it receives and preserving as much of the footage possible

What is Black and Burst Sync?

Video signal of a black image, containing synchronising pulses, and a colour burst from composite systems, fed from a stable source and connected to reference inputs on cameras, vision mixers etc

How does striping a tape work?

A timecode generator records onto the tape, providing timecode on a blank tape, which can then be edited over

What is tri level sync?

An analogue video synchronisation pulse mainly used for the locking of high-definition video signals, because of varying frame rates used in HD and the higher scanning frequency, the synchronising pulses had to be altered to make them more accurate

How does insert editing work on tape?

Insert editing uses both the in and out point on the track, and so the control track, which is being edited over, must last at least the length of the footage that needs to be inserted

Finish the statement: Tapes exposed to different environmental conditions should...

be allowed to acclimatise in the normal operating environment for up to 24 hour before they are used

Finish the statement: Loose or non uniformly wound tape should...

be slowly rewound completely before being replayed or put in storage.

Finish the statement: A tape which has not been played for two or more years should...

first be spooled slowly from end to end.

Finish the statement: The head or tail of each tape must...

be free of creases and any damaged tape should be removed.

Finish the statement: Tapes should be returned...

to it's container, and should never be left unattended

Finish the statement: Loose paper should not be...

left in the container as paper dust is abrasive

What does it mean if a tape format has a higher data rate?

The tape will have a better picture quality, mainly in terms of the colour definition

What was HDCAM SR and what data rate did it have in RGB mode?

HDCAM SR was the last tape based broadcast format, with a data rate of 888Mbps in RGB mode

What is modulation?

Modulation is the superimposition of the signal wave with a high-frequency carrier signal to ensure faster transmission.

Why is modulation needed?

Audio frequencies between 20 Hz and 20kHz are too low to transmit effectively

How does Frequency Modulation work?

The amplitude of the baseband signal changes the frequency of the carrier signal, the amplitude of the carrier is unchanged

What is PAL?

Phase Alternate Line is a colour encoding method for analogue television used by most of Europe.

Give the specifications for PAL:

625 interlaced lines, 25 fps, resolution of 720x576,

What are the benefits of PAL?

PAL uses phase alternation of the colour signal to remove hue errors - each odd line uses negative signal which corrects colour signal issues created upon transmission

What is NTSC?

Named for its creator, the National Television System Committee, NTSC is a colour encoding method for analogue tv used by the USA.

Give the specifications for NTSC:

525 interlaced lines, 29.97fps, resolution of 720x480,

What are the drawbacks of NTSC?

Colour hues require manual adjustment on the receiver's end due to phase errors

Why did NTSC framerate change from 30 to 29.97 fps?

When colour was initially introduced, black and white televisions could not distinguish between luminance and colour values, which created visual noise. Changing the framerate reduced visual issues

What is 3:2 Pulldown?

The conversion of 24fps film to 30fps video. One frame becomes two fields, and then the next frame becomes three fields.