Language dependency of candidate and reference voice coders in the STANAG 4591 selection procedure

When developing international standards for voice coding algorithms, it should be kept in mind that many different languages are likely to be used. Narrow band voice coders are sometimes subjectively experienced to suffer from language dependency: the performance of a coder (in terms of speech intelligibility) may depend on the language spoken. In the STANAG 4591 voice coder selection procedure, language dependency was included as a performance criterion. Out of nine candidate and reference vocoders, two were found to be significantly language dependent. By extension of the number of languages in the test from four to five, the sensitivity of the test was increased.