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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An alternative 660268 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.

Objective rating of speech intelligibility by speech transmission index Status: STI predicts the likelihood of syllables, words and sentences being comprehended. The speech signal has a standard level of 60 dB Aand cannot be used for speech intelligibility measurements.

Instead, they spent the time developing a much quicker objective method which was actually the predecessor to the STI. An MTF that is constant over the modulation frequencies indicates that the speech intelligibility is mainly determined by background noise.

This signal iwc available at 60 dB A and at a raised level of 72 dB A. Quite often, the difficulty of emitting a signal with ic correct speech spectrum and level, meant that shortcuts were taken which led to questionable results.

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Click to learn more. You may experience issues viewing this site in Internet Explorer 9, 10 or In very large spaces such as cathedralswhere echoes are likely to occur, the indirect method is usually preferred over direct method e. Normally this would present a serious problem because the slightest difference in clock rate between source and receiver would make it impossible to properly extract the impulse response. Communication Hearing Human voice Sound Waves. Learn more about the cookies we use and how ied change your settings.

Another method is defined for computing a physical measure that is highly correlated with the intelligibility of speech as 60286 by speech perception tests given a group of talkers and listeners. However, the requirement that the channel must be linear implies that the iiec method cannot be used reliably in many real-life applications: Your basket is empty. RASTI was designed to be much faster than the original “full” STI, taking less than 30 seconds instead iecc 15 minutes for a measuring point.


Using the new intermittent stimulus, the speech signal levels, the impulse response and the background noise levels can be acquired in a single pass. A short history of the STI method Articles with hAudio microformats.

Acoustics Engineering – Speech Intelligibility

Since then, IEC was revised three times, the 166 revisions rev. It provides a comprehensive manual for all types of users of the STI method in the fields of audio, communications and acoustics. Manfred Schroeder writes an article in Acustica in which he showed that the modulation transfer function MTF can be derived from an impulse response. You may find similar items within these categories by selecting from the choices below:. Application of RASTI to transmission chains featuring electro-acoustic components such as loudspeakers and microphones became fairly common, and led to complaints about inaccurate results.

BS EN 60268-16:2011

With the introduction of Dirac 6 and the Echo Speech Sourcespeech intelligibility measurements can be performed very quickly and easily. Our prices are in Swiss francs CHF. The use of RASTI was even specified by some application standards such as CAA specification 15 06268 aircraft cabin PA systems for applications featuring electro-acoustics, simply because it was the only feasible method at the time.

IEC Ed 4. Subsequent revisions of the standard have added i.

The Speech Transmission Index after four decades of development. A full STI measurement with modulated noise would take at least 15 minutes. Although the STIPA test signal does not resemble speech to the human ear, in terms of frequency content as well as intensity fluctuations it is a signal with speech-like characteristics.

Find Similar Items This product falls into the following categories. 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.


The faster, easier way to work with standards. ISO open plan offices. Hence, the MTF depends on the system properties and the background noise. The STI is based on the 116 between perceived speech intelligibility and the intensity modulations in the talker’s voice, as described by Houtgast, Steeneken and Plomp.

The modulation frequencies are spread among the octave bands in a balanced way, making it possible to obtain a reliable STI measurement based on ief sparsely sampled Modulation Transfer Function matrix. The list does not include software producers that produce STI-capable acoustic measuring and simulation software.

The 116 two methods are intended for rating speech transmission performance with or without sound systems. The Echo speech source can now be used for this purpose as explained in this blog post. We use cookies to make our website easier to use and to better understand your needs.

Retrieved from ” https: Further the following standards have, as part 6268 the requirements to be fulfilled, integrated testing the STI and realisation of a minimal speech transmission index:.

This is because movement of the handheld device during a measurement would make impulse response measurements unsuitable. The electrical output always operates at the same level.

Speech Intelligibility

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. The video below will show you how open plan office measurements are prepared, performed and analyzed.

Although Schroeder 2 has shown that the MTF can also be calculated from the impulse response, handheld STIPA meters use modulated noise as a test signal, whereas most PC based simulation and measurement software uses the impulse response method. The absolute measurement of speech intelligibility is a complex science.