• Home
• Subjects
• Calculations
• Conversions
• Links
• Contacts

• #
• A
• B
• C
• D
• E
• F
• G
• H
• I
• J
• K
• L
• M
• N
• O
• P
• Q
• R
• S
• T
• U
• V
• W
• X
• Y
• Z
• Help

Articulation Index

A quantitative measure of the intelligibility of speech; the percentage of speech items correctly perceived and recorded. An articulation index of 100% means that all speech can be understood, 0% means that no speech can be understood.

Articulation Index is calculated from the 1/3 octave band levels between 200Hz and 6300Hz centre frequencies. Each of the 1/3 octave dB(A) levels are weighted according to the following criteria:

• If A-weighted 1/3 octave level lies between upper and lower limits then it will be a linear value between 0 and 1.
• If value falls above the upper limit then result =0 for that particular 1/3 octave band.
• If value falls below the lower limit then result =1 for that particular 1/3 octave band.
• Multiply all of the calculated values by the AI weighting and sum all the values to get the AI in percentage terms.

Notes:

• There are other methods of calculating articulation index. This particular method is that used within the automotive industry as a wind noise metric.
• AI is designed for use where the noise is broadband in nature.
• AI uses a limited frequency range 178Hz to 7080Hz (lower frequency of 200Hz 1/3 octave band to upper frequency of 6300Hz 1/3 octave band).
• An AI < 0.05 is representative of very poor speech intelligibility, and an AI > 0.80 represents good speech intelligibility.
• The Speech Privacy Index (PI) is derived from the AI.

 Function AIval(thrdOct, dBA) Dim tho As Range th = Array(200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300) ailow = Array(23.1,30.4,34.4,38.2,41.8,43.1,44.2,44,42.6,41,38.2,36.3,34.2,31,26.5,20.9) aiwgt = Array(1, 2, 3.25, 4.25, 4.5, 5.25, 6.5, 7.25, 8.5, 11.5, 11, 9.5, 9, 7.75, 6.25, 2.5) 	′ count throught the array 	I = 0 		For Each tho In thrdOct 			I = I + 1 			For t = 0 To 15 				If tho = th(t) Then 					AIB = ((dBA(I) - ailow(t)) / 30) * aiwgt(t) 					If dBA(I) <= ailow(t) Then AIB = 0 					If dBA(I) >= ailow(t) + 30 Then AIB = aiwgt(t) 					AI = AI + AIB 				End If 			Next t 		Next tho 	AIval = 100 - AI End Function 

See also: Articulation Class, Articulation Loss of Consonants, Decibel, Percentage Articulation Loss of Consonants, Privacy Index, Speech Intelligibility.

Subjects: Noise & Vibration