STIPA

STIPA (Speech Transmission Index for Public Address systems) is a simplified measurement method for speech intelligibility defined in IEC 60268-16:2020 §5 that approximates the full STI using a single test signal. The STIPA signal contains modulated noise with two modulation frequencies per octave band, designed to efficiently sample the modulation transfer function space. The measurement typically takes 15–20 seconds per position and correlates closely with full STI (typically within ±0.03). STIPA is the standard in-situ testing method for public address, voice alarm, and paging systems because it tests through the actual electroacoustic chain including amplifiers, loudspeakers, and room acoustics. Field instruments from NTi Audio, Brüel & Kjær, and others include built-in STIPA measurement. Regular STIPA testing is recommended annually for life-safety voice alarm systems. The qualification scale matches STI: values above 0.50 are generally acceptable for emergency announcements.