A sharp impulse carries all frequencies at once and yields the full power spectrum.

Evidence

We know from the uncertainty principle that a very short burst or impulse implies that many frequencies are simultaneously present. In some sense, a sharp tap contains all frequencies at once; we can process the data from such a tap and get the same information as sinusoidal driving (that is, the power spectrum). — Eric J. Heller, Why You Hear What You Hear- An…, 1067

Categorization

• DEFINE: Explains the core impulse-response concept: why tapping a system reveals its full frequency behavior.
• XREF: Connects to the time-frequency uncertainty tradeoff familiar from Fourier analysis and quantum mechanics. — connects to: A physical impulse excites all frequencies equally in struck instruments — David Howard, Jamie Angus, coustics and Psychoacoustics, 1290