Articulation is the fraction of speech energy audible per critical band.

Evidence

The articulation index (AI), now called the speech intelligibility index (SII) (Pavlovic, 1987), objectively measures “articulation” in individual critical bands, which is defined as that fraction of the original speech energy perceivable (i.e., between the threshold of hearing and the threshold of pain, and above the background noise). The AI can be measured by averaging the signal-to-noise ratio across all the bands. The validity of AI depends on the noise being non–signal dependent, which may not be the case with some processing. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2556

Categorization

• DEFINE: Defines the articulation index / speech intelligibility index band by band.
• XREF: Ties critical bands and thresholds of hearing to the intelligibility measure — core psychoacoustics concepts from earlier chapters.