1. Analogue vs Digital

2. Analogue  Lots of different frequencies, lots of different amplitudes  Wave recorded as it is

3. Digital  Analogue waved converted to numbers by “sampling”  Sampling means reading the amplitude and frequency of the wave many times per second and writing the numbers in bits (binary digits)  Music CDs generally have a sampling rate of 44,000 times per second

4. Digital (2)  The numbers are stored on the medium (CD, mp3, etc) and are used to recreate the analogue wave when needed (e.g. as the music is played)  Higher sampling rate, better quality, but bigger mp3 file  Lower sampling rate, poorer quality, but smaller mp3 file

5. A parallel  Stop-motion animation (e.g. Wallace and Gromit) works like digital sampling  Lots of still (digital) pictures are combined together very quickly to give the impression of smooth (analogue) movement

6. Modems  The process of taking analogue data and converting it to digital is called modulation (or encoding)  The process of taking digital data and converting it to analogue is called demodulation (or decoding)  The word Modem comes from modulator-demodulator  Modems used to be used to convert digital data from your computer for transport across the analogue telephone system  But the phone system can now handle digital traffic (ADSL) and so analogue modems are not necessary any more

7. Digital: Advantages and Disadvantages  Advantages  Data doesn’t degrade on the storage medium over time  More reliable because data integrity checks can be used even over noisy channels  Information can be encrypted  Information can be compressed  Generally cheaper to store and transmit  Disadvantages  Requires more bandwidth than analogue to send the same amount of information  Sampling error can occur at low sampling rates

8. Analogue: Advantages and Disadvantages  Advantages  Uses less bandwidth  More accurate (assuming no distortion)  Disadvantages  Data degrades easily on the storage medium (e.g. magnetic cassette tape, vinyl LP records)  Random noise and distortion on the communication channel can cause data to be completely lost

9. The Need for Conversion  Most information occurring in nature is analogue, e.g. sound and light  There is a desire among people to store and communicate this information  Storage and communication of this information is done most easily after digital conversion for the reasons already mentioned