Langford Analytic · Knowledge Base

ASD vs PSD Reference

A quick reference for the relationship between amplitude spectral density and power spectral density, with common pitfalls.

Random Vibration2 min read
referenceASDPSDconversionsquare root

Relationship

ASD = √PSD
PSD = ASD²

ASD units: g/√Hz
PSD units: g²/Hz

Same RMS either way:
  RMS = √(∫ PSD df) = ∫ ASD df

Common pitfalls

  • Entering ASD value where PSD is expected — response too low by √ASD
  • Entering PSD value where ASD is expected — response too high by PSD²
  • Not confirming which form the tool expects