Conversion: STI ALcons RASTI - sengpielaudio Eberhard Sengpiel
 
Deutsche Version UK-flag s/w - sengpielaudio D-flag - sengpielaudio
 
Intelligibility  Conversion
 
%ALcons = Articulation Loss of Consonants in % ← → STI = Speech Transmission Index
 
The understanding of speech (speech intelligibility) is directly dependent of the background
noise level, of the reverberation time and of the size of the room. For the rating of the
understanding of speech, we have different methods, where STI and %ALcons are established.
 
Fill out the respective box and click the 'calculate' bar below.

 
STI   |   ALcons  %
   |   
       |       
   |   
 ALcons  %  |  STI 
   |   

Rainbow line - sengpielaudio

AlC - STI Formula

This conversion is to be regarded with some doubts,
because there are different evaluations of measurements.

The Speech Transmission Index STI is a machine measure of intelligibility whose
value varies from 0 (Completely unintelligible) to 1 (perfect intelligibility).

STI-Scale - sengpielaudio

STI 0 - 0.3 0.3 - 0.45 0.45 - 0.6 0.60 - 0.75 0.75 - 1.0
   unexceptable           poor                    fair                   good              excellent     
 ALcons  100 - 33% 33 - 15% 15 - 7% 7 - 3% 3 - 0%

Since %ALcons expresses loss of consonant definition, lower values are associated with greater intelligibility. Zero %ALcons indicates perfect clarity. It is generally assumed that the maximum allowable value for typical paging applications is 10 %, assuming that the environment is relatively free of masking noise. For learning environments and voice warning systems, the desired value is 5 % or less.
 
We know of the characteristic nonlinear decrease of intelligibility with distance from the sound source.

There is an empirical conversion formula after Farrel Becker:
Becker Formla

 
STI   
 
       
 
 ALcons  %  
 

ALcons and STI

Umrechnung: STI ALcons RASTI - sengpielaudio

For r < 3.5 × Dc at which direct/reverberation ratio D/R = −11 dB

weiter

where
Dc = Critical distance
r = Distance from the nearest loudspeaker
T60 = RT (averaged over 1 and 2 kHz)
V = Volume of the room
Q = Directivity of the nearest source
M = Acoustic modifier for reverberant power = 1 is a conservative assumption
(1 + n) = Total number of equal sources
K = Listener factor ≈ 2 % for a good listener. For
r > 3.5 × Dc (Reverberant field, always worse than above)
%ALcons = 9 × T60 + K
%ALcons < 10 % intelligibility is very good
%ALcons < 15 % intelligibility is acceptable
%ALcons > 15 % intelligibility will be a problem
 
Quantity to be measured Unit of measurement Good values
%ALcons Articulation loss (popular in USA) < 10 %
C50 Clarity index (not widespread) > 3 dB
STI (RASTI) Intelligibility (international known) > 0.6
 
Not only take something from this website to enhance your knowledge. Please,
give also some feedback to the writer of these ideas to improve the performance.
 
back zurück Search Engine weiter home start