Analogue an Digital Signals

01001011010011001001010010010010

How many things use digital or analogue signals

• Digital Analogue

TV

Radio

Talking

vinyl

watch

Mp3 playerCamera

Orchestra

Analogue TV

How are digital television pictures sent?

The TV program is filmed,This is a real life analogue signal

It is converted to a Digital signal

The signal is transmitted using radio waves

It is received by your aerialand decoded at your house

Watch TV

Make your own signal

0 = 01 = 12 = 103 = 114 = 1005 = 1016 = 1107 = 1118 = 10009 = 100110 = 1010

7

111 110

-4

-3

-2

-1

0

1

2

3

4

1 Sec

Sampled at 2 Hz

Signal Consisting of 1 Hz, 5 Hz and 10Hz

-4

-3

-2

-1

0

1

2

3

4

1 Sec

Sampled at 5 Hz

Signal Consisting of 1 Hz, 5 Hz and 10Hz

Here we seem to obtain a good sin wave at a frequency which was not present in the original signal. This is called ‘Aliasing’.

-4

-3

-2

-1

0

1

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4

1 Sec

Sampled at 10 Hz

Signal Consisting of 1 Hz, 5 Hz and 10Hz

-4

-3

-2

-1

0

1

2

3

4

1 Sec

Sampled at 20 Hz

Signal Consisting of 1 Hz, 5 Hz and 10Hz

-4

-3

-2

-1

0

1

2

3

4

1 Sec

Sampled at 40 Hz

Signal Consisting of 1 Hz, 5 Hz and 10Hz

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

A Noise Signal

Analog Signal with Noise (Large Signal to Noise Ratio)

-4

-3

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-1

0

1

2

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4

-4

-3

-2

-1

0

1

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4

Analog Signal with medium Signal to Noise Ratio

The signal can be recovered reasonably well by smoothing (but each time we do this the corruption is increased.)

-6

-4

-2

0

2

4

6

Analog Signal with small signal to noise Ratio

Even if we try to recover the signal by smoothing it is corrupted.

0

0.2

0.4

0.6

0.8

1

1.2

Digital Signal

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Digital Signal Signal with quite large signal to noise ratio.

The signal only consists of ‘1’s and ‘0’s so it can be recovered exactly.This can be done as many times as necessary.

The advantages of digital signals

The disadvantages of digital

In pairs discuss

Unwanted noise

quality

Quantity of information

Unwanted errorsEasy to use

The advantages of analogue signals

The disadvantages of analogue

simple

complicated

Needs extra equipment

Difficult for humans to understand

Easy for computers to work with

Write your own code and swap with your neighbour to decode

A 0 B 1C 10D 11E 100F 101G 110H 111I 1000J 1001K 1010L 1011M 1100N 1101

O 1110P 1111Q 10000R 10001S 10010T 10011U 10100V 10101W 10110X 10111Y 11000Z 11001

Put commas between the words to help the decoding

Encoding