Representing Data

Sample rate

Number of audio samples captured per second measured in hertz

How does sample rate affect file sizes?

More samples = more accurate reproduction = better quality = larger file sizes

Bit depth

Number of bits available for each sample, higher depth is greater quality

Bit rate

data (bits) processed in a given time, measured in kbps, higher rate is more accurate

Analogue signal

continuous varying signal to represent physical quantity e.g sound waves

Analogue to digital converter (ADC)

Converting analogue signal into digital format for a computer to store

Need for ADC

Computers can’t process analogue signals so data must first be converted to digital

Units for frequency

Hertz

Data

raw facts and figures with no meaning

Information

data entered into a computer and processed, giving it meaning

Binary

number system in bits used by computers

Bit

smallest unit of digital data represented by a 1 or 0

Nibble

4 bits

Byte (B)

8 bits, used to represent 1 character

Kilobyte (Kb)

1024 bytes

Megabyte (Mb)

1024 kilobytes

Gigabyte (Gb)

1024 megabytes

Terabyte (Tb)

1024 gigabytes

What are units of data used for?

to describe memory capacity

Numeric (integer)

positive or negative whole numbers

Numeric (real)

positive or negative numbers, including decimal/ fractional parts

Data/time

represents date and time in multiple formats

long date: DAY MONTH YEAR
medium date: DD-MMM-YYYY
short date: DD/MM/YYYY

long time: HH:MM:SS
medium time: HH:MM AM/PM
short time: HH:MM

Character

single letter or digit represented by codes from character set

ASCII

character set with each character represented uniquely by a single byte

String (text)

textual data in the form of a sequence of characters

Pixel

Smallest unit of an image displayed with its own colour

Resolution

the quality of an image, determined by the number of pixels

Effect of resolution on file size

Higher the resolution, the greater the number of pixels, and therefore too the file size

Typical bits per pixel (JPEG)

24 bits (16.7million colours)

Bitmap graphics

Stored as a grid of pixels, each with a specific colour and can be compressed

Vector based graphics

mathematical instructions to create shapes and lines

Bitmap vs vector based graphics

• Bitmap loses quality when resized while vector scales to retain detail

• Vectors more efficient, they don’t store each individual pixel

• Bitmaps can be compressed to reduce their file size

Formats for bitmap graphics

• .bmp

• .dib

• jpeg

• gif

• tiff

• .png

Formats for vector based graphics

• .svg

• .cgm

• .odg

• .eps

• .xml

Streaming

allows videos to be viewed on a website without downloading or a time delay

How does streaming work?

downloading in ‘real time’ to prevent waiting for the entire file

Buffer

Temporary memory used to download the next part of a video before watching it

Why use buffering?

prevents possible interruptions if there are time delays in streaming