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# Chapter 3

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• 1. Chapter 3 - Sampling Converting the Real World to the Digital World…
• 2. We know that analogue signals constantly change and digital signals have a value of 1 or 0.
• 3. So how do we get digital signals?
• Digital signals are produced from the ‘real’ analogue waveform
• Digital codes represent analogue signals and therefore have to be reconstructed back into analogue signals.
Original Reconstructed 0110101100010101
• 4. Sampling
• The value of an analogue signal at a point is called a sample.
Sample
• 5. Variables in sampling
• The following can be altered when sampling a analogue waveform:
• Sampling frequency – this is how many times a sample is taken every second.
• Resolution – the number of bits used to record the value of a sample
• 6. Sampling Frequency
• The number of times that a sample is taken per second will affect the quality of the digitised information. i.e….
• 7. Sampling Frequency and Waveforms
• The sampling rate needs to be more than double the highest frequency component of the waveform
• If not, aliasing can occur – this means that the reconstructed wave is not representative of the original
• 8.
• 9. Hearing Sampling…
• 10. Resolution
• The resolution is the number of ‘bits’ used to represent a value of a sample.
• 1 bit has 2 values, 0 or 1 = 2 1
• 2 bits has 4 values 0, 1, 2, 3 = 2 2
• 3 bits has 8 values, 0, 1, 2, 3, 4, 5, 6, 7 = 2 3
• The more values, the more accurate the digital sample. Note that 8 bits = a byte
• Draw a table of Number of Bits, Number of Levels and power of 2 – see page 65 for help.
• 11. 2 1 6 65536 16 … … … 2 9 512 9 2 8 256 8 2 7 128 7 2 6 64 6 2 5 32 5 2 4 16 4 2 3 8 3 2 2 4 2 2 1 2 1 2 n Number of Levels Number of Bits
• 12. Redundancy
• To prevent errors in sending digital signals, more information is sent.
• This can be seen in a CD with a scratch or hole in it…
Jarrow Sings the Blues MFI Records 1934