ARTICULATION INDEX (AI)

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A measurement, expressed as a number between 0 and 1, of the intelligibility of transmitted or processed speech or speech fragments, taking into account the SIGNAL-TO-NOISE RATIO in each of twenty speech bands.

Below 0.1, speech is considered unintelligible; above 0.6 intelligibility is acceptably high. The MASKing of onset TRANSIENTs by REVERBERATION reduces the AI by at least 0.1 for each second of reverberation time.

Compare: SPEECH COMMUNICATION CRITERION, SPEECH INTERFERENCE LEVEL.

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