Simple Sinusoids

There are four sounds to study. First listen to each of them without knowing what they are.

Did you notice that they all had the same pitch, but they sounded different. Why is it?

Let's look at each in the time domain (i.e. plotted vs. time.)

Another way to view the sounds is in the frequency domain. This is done by breaking the signal into many parts and computing the spectrum of each part. The spectra are plotted with a dark component representing a strong spectral component and white meaning no energy.

Plot Sounds in Frequency Domain

Did you notice that none of spectra changed with time? The bars were constant with time.

Even complicated sounds such as the following can be represented in the frequency domain:

This sound is noisy and harsh to the ear. It turns out that this signal contains all frequencies with equal power and is, therefore called "white noise."

Plot Noise vs. time and frequency.

Go up a level then to "chirps" or "real sounds" to see some sounds that do change with time.

Revised on 21-Apr-96 at 1:39 by jMc