1. Audio sampling as an example of analogue to digital Mr S McIntosh

2. Analogue to digital Analogue signals are continuous waves The vibrations of air particles that make up the sound is converted to a variable voltage in a transducer. Analogue recording methods such as tape and vinyl record this analogue wave in some way.

3. Analogue to digital Analogue sounds are a continuous wave. Modern data storage needs to convert this varying voltage in to a string of binary digits to allow it to be stored. 1001010110 10111100101 01010001011 10101010

4. Sampling Converting an analogue wave to digital requires SAMPLING. The amplitude of the wave is measured repeatedly and this value recorded The more often you sample the more information from the original wave you save

5. Sampling By sampling more often you save more information from the original wave

6. Sampling Each time the wave is sampled the amplitude of the wave is measured The amplitude of the wave is split into ‘Levels’. These levels can each be given a binary number The more binary digits used to represent the amplitude the more levels you can have

7. Binary Levels 2 bit binary sampling would give… 4 possible levels

8. Binary Levels 3 bit binary sampling would give… 8 possible levels

9. Binary Levels 4 bit binary sampling would give… 16 possible levels

10. Binary Levels The more bits you use the more levels you have and the closer to the ‘correct’ amplitude you will get The actual amplitude at a sample point can be between the available levels. If this happens then the closest level is used This difference is called the QUANTIZATION error

11. Sampling example Sample rate is 5kHz

12. Sampling example 8 2 4 5

13. 8 2 4 5 These numbers are then recorded as their binary equivalent Bit value8421 5 2 4 8 1 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 The 0s and 1s are recorded and the analogue wave is now stored as digital data 1000 0010 0100 0110

14. Pulse-code modulation (PCM) Number bits gives number of available levels More bits means less quantization error Sample frequency sets the time period for sampling.