Waterfall / CSD Plots
A waterfall plot shows what keeps ringing after the signal stops. The clean system drops away fast. The problem system leaves a ridge that hangs on in time.
Tiny Version
A clean decay falls off quickly. A long ridge means something is still singing after it should have shut up.
How To Read It
- Front face - the response right when the signal stops.
- Depth - how long the sound keeps ringing.
- Tall ridge reaching backward - a resonance that is decaying too slowly.
- Quick drop-off - a cleaner, tighter result.
Practical Rules
- Many systems start to sound muddy when a problem band takes more than roughly 100-150 ms to decay 30 dB.
- Deep bass can take longer naturally, especially below 80 Hz.
- A narrow ridge is often easier to chase than a broad hump because it points toward one specific structure or cavity.
Common Causes
- 40-120 Hz - doors, trunk metal, roof, or cabin panels.
- 200-500 Hz - enclosure walls or interior cavity issues.
- 800-2000 Hz - dash, trim, or smaller panel chatter.