1. Analogue and Digital Signals We seem to live in an analogue world – things can be louder or quieter, hotter or colder, longer or shorter, on a “sliding scale”. Next >>

2. Analogue and Digital Signals We seem to live in an analogue world – things can be louder or quieter, hotter or colder, longer or shorter, on a “sliding scale”. If we record sound on a tape recorder, we’re putting an analogue signal onto the tape. Next >>

3. Analogue and Digital Signals We seem to live in an analogue world – things can be louder or quieter, hotter or colder, longer or shorter, on a “sliding scale”. If we record sound on a tape recorder, we’re putting an analogue signal onto the tape. Digital signals aren’t on a sliding scale – they’re either ON or OFF. (We call these “1” and “0”.) There’s no “in between”. Next >>

4. Analogue and Digital Signals Are these analogue or digital? Next >> 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 Signals A security floodlight switches on when you approach. It has an analogue input (how much infra red it sees from you), and produces a digital output (the floodlight is either on or off). We could call it an “analogue to digital converter”. Next >>

6. Analogue and Digital Signals The problem with analogue signals is noise – hiss on the sound and speckly dots on the picture. Next >>

7. Analogue and Digital Signals The problem with analogue signals is noise – hiss on the sound and speckly dots on the picture. When we send a signal over a long distance, the signal gets weaker, so we need to boost (amplify) it. Next >>

8. Analogue and Digital Signals The problem with analogue signals is noise – hiss on the sound and speckly dots on the picture. When we send a signal over a long distance, the signal gets weaker, so we need to boost (amplify) it. The problem is that we end up boosting the noise as well. Next >>

9. Analogue and Digital Signals If we convert the signal into digital form, then send it, it still gets weaker and noise still creeps in. Next >>

10. Analogue and Digital Signals If we convert the signal into digital form, then send it, it still gets weaker and noise still creeps in. However, because it’s digital, the receiver can work out what the signal is supposed to look like behind all that noise, and reconstruct a “clean” signal. Next >>

11. Analogue and Digital Signals If we convert the signal into digital form, then send it, it still gets weaker and noise still creeps in. However, because it’s digital, the receiver can work out what the signal is supposed to look like behind all that noise, and reconstruct a “clean” signal. So we don’t end up boosting the noise along with the signal. This is why you get such good pictures on your digital satellite TV. Next >>

12. Analogue and Digital Signals Example: if you have a bad photocopy of a piece of text, and you photocopy that, you’ll get a worse photocopy. Next >>

13. Analogue and Digital Signals Example: if you have a bad photocopy of a piece of text, and you photocopy that, you’ll get a worse photocopy. But if you read the text yourself, the “software” in your brain can “reconstruct” the text, because you know what the letter shapes are supposed to be even though they’re blurred. Next >>

14. Analogue and Digital Signals Summary : Analogue signals suffer from noise, but don’t need such complex equipment. Digital signals need fast, clever electronics, but we can get rid of any noise. Plenary >>

15. Analogue and Digital Signals Summary Analogue signals suffer from noise, but don’t need such complex equipment. Digital signals need fast, clever electronics, but we can get rid of any noise. We can also use compression techniques to squeeze a lot of information in. Fibre optic cables have a huge bandwidth because light is such a high-frequency wave End