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sci.speech-intelligibility-STI Calculator
Calculates Speech Transmission Index (STI) or Rapid STI (RASTI) from modulation transfer functions across octave bands, rating speech intelligibility from 0 (impossible) to 1 (perfect). STI > 0.75 is good; 0.45–0.60 is fair — PA systems in airports and stations require STI > 0.50 per ISO 7240-19.
Inputs
Snr Db
Reference formula or conversion factor shown for context.
Rt60 S
Duration of the process. Make sure units match the rate inputs (seconds, minutes, or hours).
Results
STI estimate
The value at the specified point or condition.
MTF (modulation transfer function)
The type of mathematical function or operational classification determined by the calculation.
Speech Transmission Index scale
A normalised score comparing the result to a reference baseline.
intelligibility class
The classification assigned based on the computed value.
IEC 60268-16 STI method
The recommended calculation method or analytical approach for these conditions.