THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

10.5 Prediction of Speech Intelligibility: The Articulation Index 229Table 10.3. Weighting Factors as a Function of Center Frequencyfor One-Third Octave Band-Based Calculation of ArticulationIndexes. Speech Levels Given in the Second Column are Those for aTypical Male Voice at 1 m.Center frequency (Hz) Speech level (+12 dB) Weighting factor200 67 4250 68 10315 69 10400 70 14500 68 14630 66 20800 65 201000 64 241250 62 301600 60 372000 59 372500 57 343150 55 344000 53 245000 51 20less the masking level. Each frequency band’s contribution is limited to the rangebetween 0 and 30 dB. The sound level of the speech signal is based on a long-termenergy average in each frequency band, and each frequency band contribution ismultiplied by a weighting factor. The sum of the weighted contributions dividedby 10,000 yields the AI.Table 10.3, based on the division of the speech spectrum into one-third octaves,provides the data necessary to calculate AI. The first column lists the center frequencyof the one-third octave, the second column gives the typical male voicelong-term average speech level plus 12 dB at 1 m distance. The weighting factorfor each one-third octave band is listed in the third column. If the masking noisehas been measured only in full octave bands, Table 10.4 may be used instead ofTable 10.3.Table 10.4. Weighting Factors for One Octave Band-BasedCalculation of Articulation Indexes. This is for the Typical MaleVoice Level at 1 m.Center frequency (Hz) Speech level (+12 dB) Weighting factor250 72 18500 73 501000 78 752000 63 1074000 58 83