Impulse Response
An [see page 15, impulse] signal is an instantaneous pulse of energy, it the same amplitude at all frequencies in the frequency domain.
An impulse signal has a flat frequency-space graph (like white-noise). When passed through a filter the impulse produces the exact same frequency-space graph as the filter. Meaning if our filter has the same frequency-response (shape) as a vowel sound, passing an impulse [see page 17, through] the filter will produce the same vowel sound. This is known as source-filter modelling.