Waterfall / CSD Plots

Illustration in preparation Description: 3D CSD waterfall with annotations: time axis (0 to 500 ms), frequency axis (20 Hz to 5 kHz), level axis; arrows pointing to a resonance ridge at 95 Hz labeled "panel resonance — dampening needed" and a clean decay region labeled "good transient response"

How to read time axis:

Left face of waterfall = time zero (immediately after signal stops) Going back (depth) = increasing time after signal ends A frequency that appears only at time zero has decayed instantly — excellent. A frequency that extends far back has lingered — a resonance.

Practical threshold:

Any frequency taking more than 100–150 ms to decay 30 dB is problematic for most music. Bass frequencies (below 80 Hz) naturally take longer due to longer wavelengths — allow 200–300 ms there.

What ridges indicate:

• 40–120 Hz ridge: Vehicle panel resonance (doors, trunk floor, roof)
• 200–500 Hz ridge: Enclosure wall resonance or interior cavity
• 800–2000 Hz ridge: Dashboard or door trim resonance
• Above 2 kHz ridge: Much less common, usually thin metal panel