● Representation of sound-
○ Sound is a form of analogue data
○ Hence to record sound we need to sample the sound, we do
this by measuring the amplitude of the sound waves.
○ To record the sound waves we measure the amplitude of the
sound at regular time intervals, we can't do this precisely so we
take approximated values.
○ Let's say the amplitude range is from 0 to 10, value can be
represented with 4 bits, this is known as the sampling
resolution, but a low amplitude range generally gives inaccurate
results hence a higher range like 0 to 127 would give much
better results.
○ Also if the amplitude range is high the sampling resolution will
have to be higher, if the amplitude range is 0 to 127 we will
need 7 bits per sample.
○ The sampling resolution is also called the bit depth.
● Representation of images-
○ An image is made up of pixels which is basically a part of an
image that stores some binary value which tells us what color
this pixel is.
○ The number of bits used to represent one pixel is called the
color depth.
○ If the picture is in black and white, the color depth is 1 as each
pixel can be either 1 for white and 0 for black.
○ If the color depth is 4 then 4 bits are used to represent each
image.
○ Lets say the image resolution is 1960x2000 and the color depth
is 8, the number of bits would be-
○ 1960 * 2000 = 3, 920, 000 − 𝑡ℎ𝑖𝑠 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑖𝑥𝑒𝑙𝑠
○ 3, 920, 000 * 8 = 31, 360, 000 − 𝑡ℎ𝑖𝑠 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡𝑠
○ 31, 360, 000 / 8 = 3, 920, 000 − 𝑡ℎ𝑖𝑠 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑦𝑡𝑒𝑠
○ This step isn't required but it will be when the color depth is not
8
○ 3, 920, 000 / 1000 = 3920 − 𝑡ℎ𝑖𝑠 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑘𝑖𝑙𝑜𝑏𝑦𝑡𝑒𝑠
○ 3920 / 1000 = 3. 92 − 𝑡ℎ𝑖𝑠 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑒𝑔𝑎𝑏𝑦𝑡𝑒𝑠
○ Size conversion-
byte 8bits
kilobyte 1000 bytes
Megabytes 6
1000 kilobytes or 10 bytes
Gigabyte 9
1000 megabytes or 10 bytes
terabyte 12
1000 gigabyte or 10 bytes
● Data compression-
○ Means to reduce the data in the given file or image
○ This saves storage,
○ Reduces downloading/uploading time
○ Reduces file size and cost(in cloud storage you pay based on
the size)
○ Types of data compression-
■ lossy -
● In this the algorithm eliminates any data deemed
unworthy of living.
● The original file can not be restored once the
process is complete.
● This may apply to-
○ images - it may reduce the resolution or color
depth.
■ Example- JPEG files
○ sound - may reduce resolution or the sampling
rate.
■ Example- mp3 and mp4 files
■ Lossless-
● With this technique all the data that is compressed
can be restored. This is important for files which if
they lose data the file will no longer work.
● An example of one kind of technique is called Run
Length Encoding or RLE for short-
● It works by combining identical data that are
adjacent to each other.
● Example-
○ The text is - aaaabbbbcccc
○ Let's say a in binary is 10000
○ Let's say b in binary is 10001
○ Let's say c in binary is 10010
○ Normally the entire code is - 10000 10000
10000 10000 10001 10001 10001 10001
10010 10010 10010 10010
○ But with RLE we can convert this into- 00100
10000 00100 10001 00100 10010, this means
4 a 4 b 4 c as 00100 is 4.
○ Using RLE we halved the number of bits
required without deleting any important data.
○ Read the text book for more information
CH2-
● Data types and methods of data transmission-
○ To send data over long distances we have to break it down to
make it easier to transfer it.
○ These pisces are known as data packets
○ Each packet takes its own route from the sender to the receiver.
● Packet structure-
○ The data is divided into 3 different parts-
○ The header- it does not contain any data from the main data but
has important information nonetheless, which is-
■ Sender ip
■ Size of the data
■ Sequence of the packets
■ Receivers ip
■ Or SSSR
○ The payload- it contains the main data, it has many parts that
all have a part of the original data.
○ The trailer- it contains 2 things-
■ Some way of identifying the end of the data
■ The packet sequence to make sure there is no error in the
sequence.
■ And it stores the total number of 1s and 0s as a form of
error checking; this is called a cyclic redundancy check.
● Packet switching-
○ It is a method of data transmission, it basically sends each
packet on its own route to the receiver.
○ Each packet takes its own path
○ The routers will determine the route,
○ The route taken by each packet may not be the shortest but
due to traffic it had to take a different path which will be faster at
that point of time.
○ But the packets will reach in a different order.
○ Benefits-
■ High data transmission rate is possible
■ No need for single communication line
■ If there is too much traffic the data can be re-routed.
○ Downsides-
■ Packets can be lost during transmission so the data has
to be resent
■ Prone to error with real time streaming
■ There is delay at the destination due to the need to re
order the packets.
○ Data hopping-
■ When there is a lot of traffic everywhere the packets tend
to keep on bouncing from one route to another causing
them to get stuck.
■ To prevent this each packet is assigned a hop number
which is a value that will decrease by 1 each time the
packet bounces.
■ Let's say the packet is assigned a hop number 10, this
means that the packet can bounce 10 times the moment it
bounces once more the packet will get deleted.
■ The missing packet will be flagged by the receiver and the
data will be resent.
■ This is done to prevent a lot of packets from clogging the
routes and generating a lot of traffic.
● Modes of transmission data-
○ The mode of transmission is the way the data is sent
○ There are 3 types-
■ Simplex- where the data can be sent from device to
another but not the other way around, example-
computer to printer
■ Half-duplex- where the data can be sent from both the
directions but not at the same time, example- walkie
talkie.
■ Full duplex- where the data can be sent from both
directions at the same time, example- the internet.
● Types of data transmission-
○ There are two types-
■ Serial transmission- where the data is transferred 1 bit at
a time along a single connection one after the other
Example- USB
■ Parallel transmission- where the data is transferred
several bits or bytes at a time over multiple
connections.
Example- packet switching
○ Difference- read book (too much to write) page no 52 .
● Universal Serial Bus-
○ It is a form of serial transmission, it is used to transfer and store
data, it is the globally accepted method for input and output or
you could say physically transferring data.
●
