3 - Basic acoustics

Summary

The principles that underlie the processes of speech production and speech perception are difficult to discuss without making use of the physical concepts of wave motion, periodicity, frequency, and amplitude. These concepts are, fortunately, fairly simple and straightforward. We will also discuss the use and the physical meaning of graphs as they relate to the description of physical measurements, and conclude with an elementary description of the frequency analysis of acoustic signals and the properties of filters. Readers who have appropriate backgrounds in the physical sciences, mathematics, or engineering will undoubtedly find this chapter superfluous because we will introduce and explain these concepts by means of simple everyday examples, using a minimum of mathematical formalism. The examples that we start with – the measurement of temperature, ocean waves, and so on – have nothing to do with the acoustics of speech, but they illustrate in a direct manner the physical concepts that we want to develop.

Graphs and physical measurements

Let us start by considering the topic of graphs and their interpretation. Suppose that you were asked to read the temperature at four-hour intervals from a thermometer mounted in the shade on the back of your house. You could record the temperature that you read at each four-hour interval in the form of a list. The list, for example, might look like that in Table 3.1 for the three-day period August 7 to August 9. An equivalent way of recording this temperature information would be to make a graph.