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Language: Linguistics · Semiotics · Speech

Intelligibility is for voice communications, the capability of being understood - the quality of language that is comprehensible language or thought.

Intelligibility relates to clarity, explicitness, lucidity, comprehensibility, perspicuity, legibility, plain speaking, manifestation, understandability, precision.

The degree to which speech can be understood. With specific reference to speech communication system specification and testing, intelligibility denotes the extent to which trained listeners can identify words or phrases that are spoken by trained talkers and transmitted to the listeners via the communication system.

Intelligibility and noiseEdit

For satisfactory communication the average speech level should exceed that of the noise by 6dB, but lower S/N ratios can be acceptable (Moore, 1997). Manifesting in a wide frequency range, speech is quite resistant to many types of frequency cut-offs and/or masking. Moore reports for example that a band of frequencies from 1000Hz to 2000Hz is sufficient (sentence articulation score of about 90%). Also speech is quite resistant to distortion due to overloaded parts of the transmission as well. Even if not more than 1 or 2% of the wave's peak values is left unaffected by the distortion still scores of 80 to 90% for word articulation are being obtained (Moore, 1997)

Other factors influencing intelligibilityEdit

Excess reverberation does affect speech intelligibility.

Note: Intelligibility does not imply the recognition of a particular voice.

Measured as Speech Transmission Index = STI or in Alcons in percent.

Quantity to be measured Unit of measurement Good values
 %ALcons Articulation loss (popular in USA) < 10 %
C50 Clarity index (widespread in Germany) > 3 dB
STI (RASTI) Intelligibility (international known) > 0.6

External linksEdit


  • Moore, C.J. (1997). An introduction to the psychology of hearing. Academic Press. 4th ed. Academic Press. London
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