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AI of Fletcher and Galt (1950)

Dear Auditory List,

I have made available a computer implementation of Fletcher and Galtıs (1950) method for calculating the Articulation Index. It can be downloaded at


Fletcher and Galt's method is an alternative to the standardized methods [i.e., the ANSI AI (ANSI S3.5, 1969) and the SII (ANSI S3.5, 1997)]. It goes into much more detail than the standardized methods and the results are presumably more accurate. Fletcher and his team at Bell Labs spent about 20 years devising it but, unfortunately, it has rarely been used.(To my knowledge, in the 49 years after its publication, the procedure has been used only in 3 published studies.) This may have to do with the fact that the procedure involves lengthy computations and geometric construction which made its application tedious. It is thus understandable that many researchers and engineers opted to use simplified versions of Articulation Theory, such as those specified in the ANSI standards.

For those who do not want to spend the time reading Fletcher and Galtıs (1950) original work but still want an idea of the basic principles underlying their procedure, I have written a review that outlines the general ideas and points out some of the differences to the standardized AI methods. This review can be downloaded at the same URL.

Fletcher, H., and Galt, R. H.  (1950).  "The perception of speech and its relation to telephony," J. Acoust. Soc. Am. 22, 89-151.

-- Hannes
Hannes Müsch

Center for Communication and Digital Signal Processing
Institute for Hearing, Speech, and Language
Northeastern University
Boston, MA 02115 USA
phone: (+1) 617 373-5198  fax: x5199
email: hmuesch@ece.neu.edu