his is the first of several sections on sound. It follows the introductory multimedia tutorial Sound. Here we investigate the waveform and spectrum of sound. We also introduce some simple time-of-flight measurements of the speed of sound. (We can measure this more accurately with standing waves, which we'll meet later on.)
T
With a microphone, computer and software, you can discover a lot about sound. Audacity is just one of the free programs that allow you to record, to edit and to analyse sound. Here are some examples of the same note played on different music instruments, to display the differences in starting transient and the spectrum, both of which important to timbre.
Rather than give you explicit instructions, we leave this one as a discovery exercise. You should not confine yourself to musical instruments, of course. Try a variety of sounds.
Visualising speech is especially interesting. What is the difference between bar and car? between bar and bee? Here we give an Introduction to voice acoustics.
Speed of sound by echo
This is the first of some measurements of the speed of sound by time of flight. A short pulse of sound – here a hand clap – is recorded twice and a sound editing program used to measure the delay between the two. This is the repeat of the demonstration shown in the multimedia tutorial Sound.
Notice that, in the displayed soundtrack, we have amplified the echo. The clap is not a simple signal. Here we measured the delay between the peaks in the sound signals of clap and echo.
Speed of sound by video
This is the second of some measurements of the speed of sound by time of flight. This is also a repeat of the demonstration shown in the multimedia tutorial Sound. Typically, video recordings give 25 frames per second (although high speed cameras go much faster). So here we had to interpolate between two video frames to estimate the collision time. To do that, we assumed that the blocks were travelling at constant speed between the second frame and the collision, and used the time between second and third frames to obtain the collision time.
These time-of-flight methods are not very precise. We can do much better using standing waves, which we meet in a later chapter.
