1. 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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2. 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 puttingIf 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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3. 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 puttingIf 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’reDigital 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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4. Analogue and Digital SignalsAnalogue and Digital Signals
Are theseAre these analogueanalogue oror 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
5. Analogue and Digital SignalsAnalogue and Digital Signals
A security floodlightA security floodlight
switches on whenswitches on when
you approach.you approach.
It has anIt has an analogue inputanalogue input (how much infra red it(how much infra red it
sees from you),sees from you), and produces aand produces a digital outputdigital output
(the floodlight is either on or off).(the floodlight is either on or off).
We could call it anWe could call it an
““analogue to digital converteranalogue to digital converter”.”.
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6. Analogue and Digital SignalsAnalogue and Digital Signals
The problem with analogue signals isThe 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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7. Analogue and Digital SignalsAnalogue and Digital Signals
The problem with analogue signals isThe 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 longWhen we send a signal over a long
distance, the signal gets weaker, so wedistance, the signal gets weaker, so we
need to boost (amplify) it.need to boost (amplify) it.
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8. Analogue and Digital SignalsAnalogue and Digital Signals
The problem with analogue signals isThe 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 longWhen we send a signal over a long
distance, the signal gets weaker, so wedistance, the signal gets weaker, so we
need to boost (amplify) it.need to boost (amplify) it.
The problem is that we end up boosting theThe problem is that we end up boosting the
noise as well.noise as well.
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9. Analogue and Digital SignalsAnalogue and Digital Signals
If we convert the signal into digital form, thenIf we convert the signal into digital form, then
send it, it still gets weaker and noise stillsend it, it still gets weaker and noise still
creeps in.creeps in.
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10. Analogue and Digital SignalsAnalogue and Digital Signals
If we convert the signal into digital form, thenIf we convert the signal into digital form, then
send it, it still gets weaker and noise stillsend it, it still gets weaker and noise still
creeps in.creeps in.
However, because it’s digital,However, because it’s digital, the receiverthe receiver
can work out what the signal is supposedcan work out what the signal is supposed
to look liketo look like behind all that noise, andbehind all that noise, and
reconstruct a “clean” signal.reconstruct a “clean” signal.
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11. Analogue and Digital SignalsAnalogue and Digital Signals
If we convert the signal into digital form, thenIf we convert the signal into digital form, then
send it, it still gets weaker and noise stillsend it, it still gets weaker and noise still
creeps in.creeps in.
However, because it’s digital,However, because it’s digital, the receiverthe receiver
can work out what the signal is supposedcan work out what the signal is supposed
to look liketo look like behind all that noise, andbehind all that noise, and
reconstruct a “clean” signal.reconstruct a “clean” signal.
So weSo we don’t end up boosting the noisedon’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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12. Analogue and Digital SignalsAnalogue and Digital Signals
Example: if you have a bad photocopy of aExample: if you have a bad photocopy of a
piece of text, and you photocopy that, you’llpiece of text, and you photocopy that, you’ll
get a worse photocopy.get a worse photocopy.
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13. Analogue and Digital SignalsAnalogue and Digital Signals
Example: if you have a bad photocopy of aExample: if you have a bad photocopy of a
piece of text, and you photocopy that, you’llpiece of text, and you photocopy that, you’ll
get a worse photocopy.get a worse photocopy.
But if youBut 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, becausetext, because you know what the letteryou know what the letter
shapes are supposed to beshapes are supposed to be even thougheven though
they’re blurred.they’re blurred.
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14. Analogue and Digital SignalsAnalogue and Digital Signals
SummarySummary::
AnalogueAnalogue signals suffer from noise, but don’tsignals 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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15. Analogue and Digital SignalsAnalogue and Digital Signals
SummarySummary
AnalogueAnalogue signals suffer from noise, but don’tsignals 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 toWe can also use compression techniques to
squeeze a lot of information in.squeeze a lot of information in.
Fibre optic cables have a huge bandwidthFibre 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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