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A paper by Daniel Friedrichs, Dieter Maurer and Volker Dellwo entitled 'The phonological function of vowels is maintained at fundamental frequencies up to 880 Hz' was published in the Express Letters section of the Journal of the Acoustical Society of America.
The paper can be found online via the below link:
http://dx.doi.org/10.1121/1.4922534
Journal link:
http://scitation.aip.org/content/asa/journal/jasa/138/1/10.1121/1.4922534