This chapter introduces some important ideas that are fundamental to digital signal processing. If they are new to you take your time, the concepts are not easy to grasp and are best taken in small doses. An understanding of how digital systems work is not essential in order to use them but some knowledge is useful for solving problems and obtaining optimum results.

SAMPLING RATE

The concept of sampling rate was mentioned earlier. This important subject is now discussed in more detail.

What happens when a signal is sampled? A series of ‘snapshots’ of the signal is taken at regular intervals. The signal itself is continuous and represents some variable such as flow or pressure. The sampled signal is a string of regularly spaced ‘snippets’ of the continuous signal. This is very similar to the way a movie camera works: it starts with a continuous picture, that is, the real world, and takes a stream of still photographs at regular intervals. Since all digital data acquisition systems work with sampled signals rather than the continuous ones, an important question is ‘how well can a sampled signal represent a continuous signal?’ The answer is rather surprising.

Figure 3.1 shows a continuous signal coming from a transducer. Imagine that this is connected to a switch that is closed for a brief period at regular intervals as shown in Figure 3.2. When the switch is closed the signal passes through and when it is open nothing gets through, rather like a movie camera shutter which lets light through when it is open and nothing when it is closed.