1.2 Text, Sound & Images

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ASCII

• 7 bit codes

• 32 control codes

• Stands for American Standard Code for Information Interchange

• Extended ASCII uses 8 bit codes

• Main disadvantage is that it doesn't represent the characters in non-Western languages

Character set -> all the characters & symbols that a computer can represent where each character & symbol is assigned a specific value.

Unicode

ASCII has now been updated to Unicode:

• More efficient (uses a variable-length encoding system)

• Universally accepted (as it works with all languages)

• Uniform encoding

• Main disadvantage is that file sizes are larger so it's slower when working with text based data

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Sound

Sound is analogue (i.e. it varies continuously). Due to this, sound waves need to be sampled for a computer. An ADC (analogue to digital converter) is used for this.

Sound is sampled at regular time intervals. Increasing the number of possible sound values used to represent sound amplitude (i.e. increasing the sampling rate will increase the accuracy of the sampled sound).

Sampling resolution -> the number of bits per sample (bit depth)

Sampling rate -> the number of sound samples taken per second (measured in Hz)

Benefits	Drawbacks
Larger dynamic range	Needs greater processing power
Better sound quality	Larger file size
Less sound distortion	Takes longer to transmit or download files

Two examples of sound files are MIDI and MP3:

MIDI doesn't actually store the sound. It stores when a note should be played, how long it plays for, etc. It stands for Musical Instrument Digital Interface.

MP3 records a recording of the sound. It is a format for digital audio.

Sample answer (if asked about a MIDI file):

Musical Instrument Digital Interface Doesn't record actual sound Stores instructions for how the instruments should be played Specifies the duration, volume, and type of instrument to use Data in the file has been recorded using digital instruments

If asked about calculating the file size of a mono sound file:

Equation -> sampling rate (Hz) x sample resolution (bits) x length (sec) = file size

Then divide the total number of bits by 8 to get the file size in bytes. You may need to do further conversion if dealing with larger file sizes.

If the question asks about stereo sound, make sure to do the above equation and then multiply the answer by 2.

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Bitmap Images

An image is made up of pixels. Each pixel can be represented by a binary code. The image resolution is determined by how many pixels there are in an image. The more pixels the higher quality the image will be.

Colour depth -> the number of bits used to represent each colour

Image resolution -> the dimensions of an image (pixels [width x height]), number of pixels

Think about it like this; if you have a low resolution image (e.g. 1080p) and you zoom in, the quality starts to deteriorate very quickly and looks really bad. However, if you have a high resolution image (e.g. 8k), and you zoom in, the quality may deteriorate a little bit, but zoomed in the same percentage as the 1080p image, this one will look significantly sharper.

This image shows the difference between the number of pixels in each image resolution stop (8K being the one with the highest pixel density). Higher pixel density = better image quality & resolution.

If asked about calculating the file size of an image:

Equation -> image resolution (pixels [width x height]) x colour depth (bits) = file size

Then divide the total number of bits by 8 to get the file size in bytes. You may need to do further conversion if dealing with larger file sizes.

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Exam Questions

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