Unit 3

• Computers use a binary number system consisting of only 0s and 1s • Everything that a computer needs to process must be converted into binary format • This format is used for storing numbers, text, images, sound and program instructions

• BMP • JPG • GIF • PNG • TIFF

The number of bits per pixel

The number of bits per sample

72 PPI (Pixels Per Inch)

More bits per pixel = more colour combinations - 1 bit = 2 colours - 2 bits = 4 colours - 3 bits = 8 colours - 4 bits = 16 colours

• Each pixel can represent a finite number of colours • A pixel is attributed a number of n bits • The number of combinations (2^n) dictates the bit depth and therefore the number of colours that can be represented • A higher bit depth gives a greater range of colour and a better quality of image

An increase in the number of colours that are used in an image (the bit depth) will increase the file size

• Size has two meanings • An increase in the number of pixels in the image will increase the file size • If an images physical size is increased by making each pixel larger than there is no change in the file size

• Analogue sound signals are continuous • Digital signals are discrete, this means the sound wave is sampled at regular intervals

• Sounds must be converted into a digital from in order to be stored and processed by a computer • An Analogue to Digital Converter (ADC) is used to convert inputs to digital signals • A Digital to Audio Converter (DAC) is used to convert digital signals to outputs ADC –> Processing –> DAC

A measurement of amplitude of a sound wave at a given time

• Sound is sampled using a sample resolution (bit depth) and sampling rate • The sample resolution determines how closely the wave is sampled on the y-axis

• The sampling rate is the number of samples taken per second. It is measured in hertz (Hz) • The frequency or sample rate per second affects the level of detail in the digital representation • The greater the frequency, the greater the accuracy and file size

• The number of bits used to record each measurement • More bits used per sample enables the height of the wave to be more accurately measured but increases the file size

Lossless compression formats are able to reduce the file size when compressed but not lose any information

• FLAC (Free Lossless Audio Codec) • ALAC (Apple Lossless Audio Codec) • WMA Lossless (Widows Media Audio)

• Lossy compression removes sounds that we can’t easily hear or that least affect the perceived playback quality • Lossy compression leaves out some data from the original so can negatively affect the sound quality • Useful for storing, downloading or streaming

sampling rate x bit depth x duration

• MP3 • AAC (Advanced Audio Coding)

Reducing the size of a file

Reduces the size of a file so it takes up less disk space, and is quicker to download over the Internet

8 bits = 1 byte

7 bits