computer science - data representation

what is sound

what is sound

a type of analog signal that is captured and converted into digital form to be processed by a computer

how is sound converted into digital form

by sampling. (taking measurements of the sound wave at regular intervals and converting these measurements into binary)

what is the sample resolution

the number of bits per sample, determines the level of detail of each sample

what are the two types of sound files

MIDI and MP3

describe MIDI

Musical Instrument Digital Interface (file)
Stores a set of instructions (for how the sound should be played)
It does not store the actual sounds
Data in the file has been recorded using digital instruments
Specifies everything important so
Individual notes can be edited

describe MP3

MP3 is a format for digital audio
MP3 is an actual recording of the sound
MP3 is a (lossy) compression format
It is recorded using a microphone

how are images represented

using a bitmap (series of pixels)

what are pixels

small dots of colour that are arranged in a grid. each pixel can be represented by a binary code

how does the file size of an image increase

when the resolution and colour depth increase

how many bytes are in
Kibibyte (KiB)
mebibyte (MiB)
gibibyte (GiB)
tebibyte (TiB)
pebibyte (PiB)
exbibyte (EiB)

2^10 bytes
2^20
2^30
2^40
2^50
2^60

describe lossless compression

-reduces size without permanently removing data
-repeated patterns are identifies and indexed
- run-length encoding (RLE) and huffman encoding is used
-RLE replaces sequences of repeated characters with a code that represents the character and the number of times it is repeated
-huffman encoding replaces frequent characters with shorter codes and less frequent characters with longer codes

what is text

a collection of characters that can be represented in binary

how do computers represent text in binary

using a character set - a collection of characters and the corresponding binary codes to represent them

what the most common character set

ASCII
which assigns a unique 7-but binary code to each character

what a flaw of ASCII

limit in terms of the number of characters it can represent and doesnt support non-western languages

how are the ASCII problems solved

unicode was developed, which can represent a larger variety of characters (uses 8 or 16 bits)

How does Unicode work?

uses a variable - length encoding scheme that assigns a unique code to each character, which is represented in binary using several bytes

whats the negatives of unicode

requires more bits per character than ASCII, it can result in larger file sizes and slower processing times when working with text-based data

what does the quality of digital sound depend on

on the sample rate (number of samples taken per second) the higher the rate the higher the quality, however also increases file size

what is a typical CD sample rate and resolution

44.1 kHz and 16-bit binary

what affects the resolution of an image

the number of pixels in the image, higher resolution = more pixels = more detailed but more storage space

how many colours can an 8-bit colour depth allow

2^8 so 256 different colours

what is the colour depth of an image

the number of bits used to represent each colour. the higher the colour depth = more colours = more storage

An image has a resolution of 600 x 400 and a colour depth of 1 byte. Calculate the file size of the image giving your answer in bytes

600 x 400 = 240000

what is the smallest unit of data storage

1 bit (either 0 or 1)

how many bits is a nibble

4 bits

how many bits is a byte

8 bits

how to calculate image file size

resolution (width x height) x colour depth (number of pixels)
(if question is in bytes, divide number of bits by 8)

find image size in bytes, An image measures 100 by 80 pixels and has 128 colours

resolution = 100 x 80 = 800
colour depth = 2^7 = 128 so 7
size = 800 x 7 = 56000bits
bytes = 7000

how to calculate file size of sound

Sample rate (hz) x sample resolution (bits) x length of sample (seconds)

calculate size: A sound clip uses 48KHz sample rate, 24 bit resolution and is 30 seconds long

bits per second = 48000 x 24
size = 1152000 x 30 = 34560000
bytes = 4320000
kibibytes = 4218. 75 (divide 1024)
mebibytes = 4.12 (divide 1024)

what are the two types of compression

lossless and lossy

why is compression necessary

to reduce the size of large files for storage, transmission and faster processing

when is lossless used for

for text, code and archival purposes as loosing data would be a problem

describe lossy compression

-reduces file size permanently
-used to images and audio, where minor details can be removed without impacting the quality
-uses downscaling, reducing resolution or colour depth and reducing samples or rate
-amount of data removed depends on the level of compression selected and can impact the quality of the final file

what is lossy compression used for

for media files like audio or images where minor data loss is accpetable