Speech Intelligibility
The Importance of Speech Intelligibility
It is absolutely vital that the speech intelligibility is high in buildings such as airports, hospitals, train stations, and other public areas. This ensures that emergency announcements will be clear and understandable. The best way to achieve this is by measuring the Speech Transmission Index (STI). The Speech Transmission Index for Public Address Systems, or STIPA, is a fast and accurate way to measure the STI of a given area, taking into account the quality of the speakers, signal interference, room acoustics, and much more.
The Importance of Speech Intelligibility
It is absolutely vital that the speech intelligibility is high in buildings such as airports, hospitals, train stations, and other public areas. This ensures that emergency announcements will be clear and understandable. The best way to achieve this is by measuring the Speech Transmission Index (STI). The Speech Transmission Index for Public Address Systems, or STIPA, is a fast and accurate way to measure the STI of a given area, taking into account the quality of the speakers, signal interference, room acoustics, and much more.
Using STIPA to Test Speech Intelligibility
The reverberation time (or RT60) is among the most commonly specified room acoustics measurements. Unfortunately, reverberation time measurements are also among the most complex to carry out accurately. Standardized procedures for measuring the reverberation time of a room are specified in ISO-3382-2. Generally speaking, there are two different ways to measure RT60: the impulse response method and the interrupted noise method. Both methods are standardized through ISO-3382-2. The interrupted noise method, as supported by the Bedrock SMxx, measures the decay of the sound field if a sound source is suddenly switched off. This method is more robust against slight inaccuracies or inconsistencies in the placement of sound source and microphone.
The Benefits of Using Full STI
Although fast and robust, STIPA has its limitations. Only 2 modulation frequencies are measured per octave band with STIPA. The complete Speech Transmission Index measurement scheme calls for 14 modulations per octave band. This means that STIPA is under-sampled in the modulation domain. For many systems, the measured STI is not (or hardly) affected. However, some cases call for Full STI measurements, like areas with excessive echoing or systems that feature complex distortion factors.
Full STI measurements were available in commercial measuring tools up to the late 1990s, but have subsequently been absent from the market for two decades. The fact that a full STI measurement used to take around 15 minutes made Full STI measurements entirely impractical. Also, the introduction of STIPA around 2002 made a reasonable alternative available. The Full STI module now available on the SM50 and SM90 fully implements every aspect of the Speech Transmission Index model and can complete a test in about a minute, making it the most universally applicable speech intelligibility metric to date.
