Curriculum Corporation
Video Research Project

What is Digitisation? (Analogue vs Digital)

Further reading

Key concepts

  • In an analogue medium such as an LP record, information is recorded in the form of a direct physical correspondence between the medium and the event that is being captured.
  • Digital representation involves measuring the original event at frequent intervals and storing those measurements as a string of digitally encoded numbers.
  • The greater the range of numbers available, the greater is the accuracy and quality of the digitised result.
  • Data imported into a computer takes up space; the more information used, the greater the storage space required.

Introduction

Picture in your mind a flower. In the centre, the petals are a rich purple. As you follow the petals towards their tips, the colour very gradually changes to a pale pink. This gradation of colour is incredibly subtle; at no stage is there an abrupt transition.

This flower is part of the inherently analogue world in which we live, a world composed of an infinitely varying palette of colours, sounds, tastes and textures. Our senses too are analogue, conveying sensation through electrical pulses and chemical reactions in sense organs such as the eyes and ears. These biological processes vary in accord with changes in the external world. There is an analogous relationship.

Similarly, the capacity of analogue media to capture an image of a flower or the ring of a bell relies on some form of direct physical change within the medium itself that reflects the character of the external environment.

A vinyl record is a good example of an analogue media format. The pattern of the grooves pressed into the surface of the record mimic the pattern of variation in air pressure associated with the original sound. When the record is played back, the sound wave is recreated for the enjoyment of the listener.

Digital media present a stark contrast. The development of digital electronic systems has profoundly changed the way information is captured, processed, stored and shared. Digital representation literally involves the use of digits or numbers in representation.

Where do these numbers come from?

The digitisation process produces a stream of digital information. This information comes from measurements of the original analogue phenomenon as shown in Figure 1

Figure 1: Measurements of the original analogue phenomenon
Figure 1Measurements of the original analogue phenomenon

To represent this analogue sound wave digitally, we measure (or sample) the amplitude (height) of the sound wave at frequent intervals. In this case, we measure the amplitude on a scale that ranges from a minimum of zero to a maximum of 255. This gives a range that contains 256 separate intervals - a convenient number for digital storage because it corresponds to the information storage capacity of a single {glossary:byte}Byte{~glossary} of computer memory.

Audio CDs store each sample using two bytes, yielding 16,384 potential values. This enables a much more fine-grained representation, and the reproduction of the original sound with a much higher fidelity. Since a {glossary:byte}Byte{~glossary} consists of eight individual {glossary:binary}Binary{~glossary} digits or {glossary:bit}Bits{~glossary}, this is also described as 16-{glossary:bit}Bit{~glossary} {glossary:sampling}Sampling{~glossary}.

This correlation between the number of {glossary:bit}Bits{~glossary} employed in every sample and the quality of the digitised result applies to all media, including images, as explored in the Image Digitisation whitepaper.

Once digitised, information can be manipulated and processed using computer programs. Digital content can also be distributed over networks - free from the costs and constraints associated with the creation and distribution of physical copies.

Remember that your computer has a limited amount of storage space! If you are {glossary:capturing}Capturing{~glossary} half an hour of high-quality footage, you will use up to 7GB of disk space. In the instance of editing and converting a {glossary:dvd}DVD{~glossary}, you will be compressing this data to an appropriate {glossary:dvd}DVD{~glossary} format, which will also use up disk space. Video editing can use up more disk space than editing other multimedia formats. If you are in doubt about your computer’s capacity, talk to your IT support people.