This document discusses how analog signals are converted to digital signals through the process of sampling. It explains that sampling involves taking the value of an analog signal at discrete points in time and converting it to a digital code. The key variables in sampling are the sampling frequency, or how many samples are taken per second, and resolution, or the number of bits used to record each sample value. The sampling frequency needs to be more than double the highest frequency of the analog waveform to avoid aliasing and get an accurate digital reconstruction of the original signal. More bits of resolution provide more possible sample values and a more accurate digital representation.

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

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