STIPA (Speech Transmission Index for Public Address Systems) is a simplified version of STI designed for practical application in specific situations (amongst others measuring PA Systems in airports and railway stations).
In STIPA testing, the preferred test signal employed is a signal with speech-like characteristics.
Speech can be described as noise that is modulated by low-frequency signals. Therefore STIPA employs a special amplitude modulation scheme to generate its test signal. At the receiving end of the communication system, the depth of modulation of the received signal is measured and compared with that of the test signal in each of a number of frequency bands. Reductions in the modulation depth are associated with loss of intelligibility.
An alternative Impulse response method assumes that the channel is linear and requires stricter synchronization of the sound source to the measurement instrument.
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