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

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.

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

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

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

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

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

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

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

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

Sampling example Sample rate is 5kHz

Sampling example

These numbers are then recorded as their binary equivalent Bit value The 0s and 1s are recorded and the analogue wave is now stored as digital data

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.