Production theory explains vowel sounds by formants in terms of a resonance pattern of the vocal tract. In perception theory normalization must also be undertaken because of different formant values for one vowel category, as found in comparisons of men, women and children, and in studies of sung vowels and of synthesized vowel sounds. Synthesis indicates a dependence of the formants on FO. Therefore, the question arises whether the formant pattern is directly related to FO when studied in real vocalizations. This study presents: a. a method to determine formant movement in real vocalizations for all FO, and b. the results of spectral and LPC analysis of the three German vowels [u:], [o:] and [a:] in real vocalizations. The need for formant movement with altering FO, as well as a change in the number of formants with altering FO, is demonstrated. The implications of these results for normalization in the description of the physics of the vowel sound wave are discussed.