An oscillating impulse response is itself an early echo, a confinement effect

Evidence

The damped-periodic oscillation (as opposed to immediate relaxation of the signal as in case A earlier) is a form of confinement, a very early echo. A resonance centered at the frequency of the oscillation f0 results (middle right); its width Δf obeys the uncertainly principle ΔfΔT ~ 1, where ΔT is the time to reach 4% amplitude. — Eric J. Heller, Why You Hear What You Hear- An…, 1110

Categorization

• DEFINE: Frames the damped oscillation itself as a confinement echo, a non-obvious conceptual bridge between transient decay and resonance.