Analogue and Digital SignalsAnalogue and Digital Signals

We seem to live in an analogue world – We seem to live in an analogue world –

things can be louder or quieter, hotter or colder, things can be louder or quieter, hotter or colder, longer or shorter, on a “longer or shorter, on a “sliding scalesliding scale”.”.

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Analogue and Digital SignalsAnalogue and Digital Signals

We seem to live in an analogue world – We seem to live in an analogue world –

things can be louder or quieter, hotter or colder, things can be louder or quieter, hotter or colder, longer or shorter, on a “longer or shorter, on a “sliding scalesliding scale”.”.

If we record sound on a tape recorder, we’re putting If we record sound on a tape recorder, we’re putting an analogue signal onto the tape.an analogue signal onto the tape.

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Analogue and Digital SignalsAnalogue and Digital Signals

We seem to live in an analogue world – We seem to live in an analogue world –

things can be louder or quieter, hotter or colder, things can be louder or quieter, hotter or colder, longer or shorter, on a “longer or shorter, on a “sliding scalesliding scale”.”.

If we record sound on a tape recorder, we’re putting If we record sound on a tape recorder, we’re putting an analogue signal onto the tape.an analogue signal onto the tape.

Digital signals aren’t on a sliding scale – they’re Digital signals aren’t on a sliding scale – they’re either ON or OFF. (We call these “1” and “0”.) either ON or OFF. (We call these “1” and “0”.) There’s no “in between”.There’s no “in between”.

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Analogue and Digital SignalsAnalogue and Digital Signals

Are these Are these analogueanalogue or or digitaldigital??

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Volume control on a radio

Light switch

Traffic lights

Water tap

Dimmer switch

Motor bike throttle

Music on a CD

Music on a tape

Analogue and Digital SignalsAnalogue and Digital Signals

A security floodlight A security floodlight

switches on whenswitches on whenyou approach. you approach.

It has an It has an analogue inputanalogue input (how much infra red it (how much infra red it

sees from you),sees from you), and produces a and produces a digital outputdigital output (the floodlight is either on or off).(the floodlight is either on or off).

We could call it an We could call it an

““analogue to digital converteranalogue to digital converter”.”.Next >>

Analogue and Digital SignalsAnalogue and Digital SignalsThe problem with analogue signals is The problem with analogue signals is noisenoise – hiss on the sound and speckly dots on – hiss on the sound and speckly dots on the picture. the picture.

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Analogue and Digital SignalsAnalogue and Digital SignalsThe problem with analogue signals is The problem with analogue signals is noisenoise – hiss on the sound and speckly dots on – hiss on the sound and speckly dots on the picture. the picture.

When we send a signal over a long When we send a signal over a long distance, the signal gets weaker, so we distance, the signal gets weaker, so we need to boost (amplify) it.need to boost (amplify) it.

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Analogue and Digital SignalsAnalogue and Digital SignalsThe problem with analogue signals is The problem with analogue signals is noisenoise – hiss on the sound and speckly dots on – hiss on the sound and speckly dots on the picture. the picture.

When we send a signal over a long When we send a signal over a long distance, the signal gets weaker, so we distance, the signal gets weaker, so we need to boost (amplify) it.need to boost (amplify) it.

The problem is that we end up boosting the The problem is that we end up boosting the noise as well.noise as well.

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Analogue and Digital SignalsAnalogue and Digital SignalsIf we convert the signal into digital form, then If we convert the signal into digital form, then send it, it still gets weaker and noise still send it, it still gets weaker and noise still creeps in. creeps in.

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Analogue and Digital SignalsAnalogue and Digital SignalsIf we convert the signal into digital form, then If we convert the signal into digital form, then send it, it still gets weaker and noise still send it, it still gets weaker and noise still creeps in. creeps in.

However, because it’s digital, However, because it’s digital, the receiver the receiver can work out what the signal is supposed can work out what the signal is supposed to look liketo look like behind all that noise, and behind all that noise, and reconstruct a “clean” signal. reconstruct a “clean” signal.

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Analogue and Digital SignalsAnalogue and Digital SignalsIf we convert the signal into digital form, then If we convert the signal into digital form, then send it, it still gets weaker and noise still send it, it still gets weaker and noise still creeps in. creeps in.

However, because it’s digital, However, because it’s digital, the receiver the receiver can work out what the signal is supposed can work out what the signal is supposed to look liketo look like behind all that noise, and behind all that noise, and reconstruct a “clean” signal. reconstruct a “clean” signal.

So we So we don’t end up boosting the noise don’t end up boosting the noise along with the signalalong with the signal. This is why you get . This is why you get such good pictures on your digital satellite TV.such good pictures on your digital satellite TV.

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Analogue and Digital SignalsAnalogue and Digital SignalsExample: if you have a bad photocopy of a Example: if you have a bad photocopy of a piece of text, and you photocopy that, you’ll piece of text, and you photocopy that, you’ll get a worse photocopy. get a worse photocopy.

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Analogue and Digital SignalsAnalogue and Digital SignalsExample: if you have a bad photocopy of a Example: if you have a bad photocopy of a piece of text, and you photocopy that, you’ll piece of text, and you photocopy that, you’ll get a worse photocopy. get a worse photocopy.

But if you But if you read the text yourselfread the text yourself, the , the “software” in your brain can “reconstruct” the “software” in your brain can “reconstruct” the text, because text, because you know what the letter you know what the letter shapes are supposed to beshapes are supposed to be even though even though they’re blurred.they’re blurred.

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Analogue and Digital SignalsAnalogue and Digital SignalsSummarySummary::

AnalogueAnalogue signals suffer from noise, but don’t signals suffer from noise, but don’t need such complex equipment. need such complex equipment.

DigitalDigital signals need fast, clever electronics, signals need fast, clever electronics, but we can get rid of any noise. but we can get rid of any noise.

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Analogue and Digital SignalsAnalogue and Digital SignalsSummarySummary

AnalogueAnalogue signals suffer from noise, but don’t signals suffer from noise, but don’t need such complex equipment. need such complex equipment.

DigitalDigital signals need fast, clever electronics, signals need fast, clever electronics, but we can get rid of any noise. but we can get rid of any noise.

We can also use compression techniques to We can also use compression techniques to squeeze a lot of information in.squeeze a lot of information in.

Fibre optic cables have a huge bandwidth Fibre optic cables have a huge bandwidth because light is such a high-frequency wavebecause light is such a high-frequency wave

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