IEC Sound system equipment – Part Objective rating of speech intelligibility by speech transmission index. according to the standard IEC (edition 4). STI and. STIPA are the most established methods for measuring speech intelligibility. Speech Transmission Index (STI) is a measure of speech transmission quality. The absolute RASTI was standardized internationally in , in IEC . Since then, IEC was revised three times, the latest revisions (rev.4).
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The absolute measurement of speech intelligibility is a complex science. The STI measures some physical characteristics of a transmission channel a room, electro-acoustic equipment, telephone line, etc. STI is a well-established objective measurement predictor of iex the characteristics of the transmission channel affect speech intelligibility. The influence  that a transmission channel has on speech intelligibility is dependent on:.
Instead, they spent the time developing a much quicker objective method which was actually the predecessor to the STI. In the early years until approx. RASTI was designed to be much faster than the original “full” STI, taking less than 30 seconds instead of 15 minutes for a measuring point.
Acoustics Engineering – Speech Intelligibility
Application of RASTI to transmission chains featuring electro-acoustic components such as loudspeakers and 61 became fairly common, and led to complaints about inaccurate results. The use 602688 RASTI was even specified by some application irc such as CAA specification 15 for aircraft cabin PA systems for applications featuring electro-acoustics, simply because it was the only feasible method iiec the time.
TNO did produce and sell instruments for measuring full STI and various other STI derivatives, but these devices were relatively expensive, large and heavy. Since then, IEC was revised three times, the latest revisions rev.
Each revision included updates of the STI methodology that had become accepted in the STI research community over time, such as the inclusion of redundancy between adjacent octave bands rev.
An IEC maintenance team is currently working on rev. At this 60628, this simplified STI derivative was still stipulated as a standard method in some industries. STI predicts the likelihood of syllables, words and sentences being comprehended.
As an example, for native speakers, this likelihood is given by:. If non-native speakers, people with speech disorders or hard-of-hearing people are involved, other probabilities hold. It is interesting but not astonishing that STI prediction is independent of the language spoken — not astonishing, as the ability of the channel to transport patterns of physical speech is measured.
Another method is defined for computing a physical measure that is highly correlated with the intelligibility of speech as evaluated by speech perception tests given a group of talkers and listeners.
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The IEC ed4 Standard defines a qualification scale in order to provide flexibility for different applications. STI has gained international acceptance as the quantifier of channel influence on speech intelligibility. The International Electrotechnical Commission Objective rating of speech intelligibility by speech transmission index,  as prepared by the TC Technical Committeedefines the international standard.
Further the following standards have, as part of the requirements to be fulfilled, integrated testing the STI and realisation of a minimal speech transmission index:.
Within the STIPA signal, each octave band is modulated simultaneously with two modulation frequencies. The modulation frequencies are spread among the octave bands in a balanced way, making it possible to obtain a reliable STI measurement based on a sparsely sampled Modulation Transfer Function matrix.
Although the STIPA test signal does not resemble speech to the human ear, in terms of frequency 61 as well as intensity fluctuations it is a signal with speech-like characteristics.
Speech can be described as noise that is intensity-modulated by low-frequency signals. The STIPA signal contains such intensity modulations at 14 different modulation frequencies, spread across 7 octave bands. 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, also known as the “indirect method,” assumes that the channel is linear and requires stricter synchronization of the sound source to the measurement instrument. The main benefit of the indirect method over the direct method based on modulated test signals is that the full MTF matrix is measured, covering all relevant modulation frequencies in all octave bands.
In very large spaces such as cathedralswhere echoes are likely to occur, the indirect method is usually preferred over direct method e. In general, the indirect method is often the best option when studying speech intelligibility based on “pure room acoustics,” when no electro-acoustic components are present within the transmission path.
However, the requirement that the channel must be linear implies that the indirect method cannot be used reliably in many real-life applications: Also, depending on 06268 type of impulse response 600268 that is used, the influence of background noise present during measurements may not be dealt with correctly.
This means that the indirect method should only be used with great care when measuring Public Address systems and Voice Evacuation systems. STI measuring instruments are and have been made by various manufacturers. Below is a list of brands under which STI measuring instruments have been sold, in alphabetical order. The market for STI measuring solution is still developing, so the above list is subject to change as manufacturers enter or leave the market. The list does not include software producers that produce STI-capable acoustic measuring and simulation software.
From Wikipedia, the free encyclopedia.
The influence  that a transmission channel has on speech intelligibility is dependent on: Am 67— The Speech Transmission Index after four decades of development. Vol 17, part 7. A Vol 21 Part 5. Sound system equipment — Part Retrieved from ” https: 60286 Hearing Human voice Sound Waves. Articles with hAudio microformats.
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