Digital Sound & Music: Concepts, Applications, & Science, Chapter 2, last updated 6/25/2013
Figure 2.18 Axes of Frequency Analysis and Waveform Views
In the example just discussed, the frequencies that are combined in the composite sound
never change. This is because of the way we constructed the sound, with three single frequency
waves that are held for one second. This sound, overall, is periodic because the pattern created
from adding these three component frequencies is repeated over time, as you can see in the
bottom of Figure 2.14.
Natural sounds, however, generally change in their frequency components as time passes.
Consider something as simple as the word “information.” When you say “information,” your
voice produces numerous frequency components, and these change over time. Figure 2.19
shows a recording and frequency analysis of the spoken word “information.” You can see in the
frequency analysis view on the left that there are a few high frequency components due to the “f”
sound and “sh” in the syllable “tion.”
When you look at the frequency analysis view, don‟t be confused into thinking that the x-
axis is time. The position of the “hump” on the right part of the graph indicates that there are
frequencies around 15,000 Hz, but the frequency analysis graph doesn‟t tell you where in time
these high frequency components occurred.
Figure 2.19 Frequency analysis of the spoken word “information”
A one-note song would not be very interesting. In music and other sounds, pitches – i.e.,
frequencies – change as time passes. Natural sounds are not periodic in the way that a one-chord
sound is. The frequency components in the first second of such sounds are different from the