NORMALISATION of vowel formant data

Why do sociolinguists and sociophoneticians normalize vowel formant data?


Because individual people’s heads have slightly different sizes, as well as different proportions between the oral and pharyngeal cavities (roughly, the size of the mouth vis-à-vis the size of the throat), and even differ in for example the degree of concavity of the palate. Thus, the acoustic properties of the sound wave an individual person produces when speaking aren’t really directly comparable with any another individual’s speech unless some form of mathematical normalisation takes place. We possibly all do a type of daily normalisation in our heads as well, for example, when we can understand children and adults saying the same words, even though their voices sound very different. (Not all theoreticians would agree that that is how it happens: maybe we ‘remember’, subconsciously, many fine-grained details about the utterances we hear around us, but that is another story).
Sociolinguists are crucially interested in language change, for instance in subtle differences between the pronunciations of older and younger speakers. Normalisation is one of the key procedures you need when you study vowel change, because you have to make sure that the differences you see between say, older men’s and younger women’s speech patterns, are really due to generational changes (that is, the younger generation speaks differently) and not just the fact that men’s and women’s heads are different sizes.

For more information about getting started with normalisation, see the following references:

Clopper, Cynthia. 2009. Computational methods for normalization acoustic vowel data for talker differences. Language and Linguistics Compass 3(6): 1430-42. [ Online: Compass ]


Thomas, Erik R. 2011. Sociophonetics: An Introduction. Basingstoke, UK: Palgrave Macmillan


Watt, Dominic, Fabricius, Anne, and Kendall, Tyler. 2011. More on vowels: Plotting and normalization. In Marianna di Paolo and Malcah Yaeger-Dror (eds.), Sociophonetics: A Student's Guide. London: Routledge, 107-118

And see also the NORM suite (Thomas and Kendall 2007): http://ncslaap.lib.ncsu.edu/tools/norm/index.php, which also has a bibliography