Three types of sound and their appearance

There are three main kinds of sound that are easily distinguishable on a spectrogram, corresponding to three acoustic categories. Sounds can be periodic (that is, regularly repeating), or aperiodic (that is, random). Aperiodic sounds in speech can be either continuous (like fricatives such as [s f θ]) or transient (that is, short and momentary), like [p t k]. Each has a different appearance on a spectrogram and in waveforms.

Figure 3.3 is a spectrogram of the word ‘spend’. This word illustrates the three main kinds of sound.