This site has been created by members of the Acoustical Society of America (ASA) Working Group S3-79, which is in charge of reviewing American National Standard ANSI S3.5-1997 (“Methods for Calculation of the Speech Intelligibility Index”). This standard defines a method for computing a physical measure that is highly correlated with the intelligibility of speech as evaluated by speech perception tests given a group of talkers and listeners. This measure is called the Speech Intelligibility Index, or SII. The SII is calculated from acoustical measurements of speech and noise. The site provides software for calculating the Speech Intelligibility Index (SII), as well as notes relevant to potential future changes of the standard and the listing of known errors to be corrected in the next version of the standard. You are encouraged to contact us with any information that may help make the Standard better and easier to use. Also, if you have other software that can facilitate SII calculations, we urge you to send it to us for a review and posting on this site.