Speech intelligibility can be predicted by measuring signal envelope modulation decay

Evidence

If that were not enough, he also made substantial contributions to our knowledge of speech perception and developed a tool (originally called the Articulation Index, now revised to the Speech Intelligibility Index [SII]) that allows one to calculate the amount of speech information available in different frequency bands. The SII is able to robustly predict intelligibility scores for certain speech materials and acoustic environments (ANSI- 3.5, 2017) and is now used in industrial applications and to assess the impact of hearing loss on speech perception. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 90 (#expands, via linked claim)

The direct component is important because it carries the information in the signal in an uncontaminated form. Therefore a high level of direct sound is required for a clear sound and good intelligibility of speech. The direct sound also behaves in the same way as sound in free space, because it has not yet interacted with any boundaries. This means that we can use the equation for the intensity of a free space wave some distance from the source Figure 6. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1729 (#complicates, via linked claim)

The direct sound: This is the sound that carries information and articulation. For speech it is important that the listener receive a large amount of direct sound if they are to comprehend the words easily. Unfortunately, as discussed in Chapter 1, the direct sound gets weaker as it spreads out from the source. Every time you double your distance from a sound source the level of the direct sound goes down by a factor of four, that is, an inverse square law. Thus the further away you are from a sound source, the weaker the direct sound component. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2434 (#complicates, via linked claim)

Categorization

• XREF: connects to: Speech intelligibility in rooms can be predicted from fluctuation strength — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 2059; Speech intelligibility depends on conserving envelope modulation through a channel; Speech intelligibility indexes average signal-to-noise ratio across critical bands — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 90 (+3 more)

Broader Connections

• Speech intelligibility indexes average signal-to-noise ratio across critical bands #expands (0.78) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 90
• Direct sound carries signal information uncontaminated and governs speech intelligibility #complicates (0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1729
• Speech intelligibility depends on high direct-to-reverberant sound ratios #complicates (0.74) — David Howard, Jamie Angus, coustics and Psychoacoustics, 2434
• Reverberation time and signal-to-noise ratio map onto the same speech intelligibility scale #expands (0.72)