- 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.
- 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
AIval = 100 - AI
Subjects: Noise & Vibration