Reading Spectrograms

When analyzing chirps (variable-frequency sounds), it doesn't make sense to talk about the "frequency domain" since the frequency itself is a function of time. In even more complex waves, the frequency might be a variable that isn't constant or a function of time. A more helpful way of visualizing these sound signals is to look its spectrogram. A spectrogram is a three-dimensional visualization that shows time on the x-axis, frequency on the y-axis, and the frequency's energy at a particular time using color. The "domain" of this visualization is both time and frequency together.