I am trying to synthesize the French vowels [o] and [ɔ] for running a perception experiment. I have been using the Praat Vocal Toolkit and got pretty nice results with the following formant values: F1(o)=430, F2(o)=800 Hz, F1(ɔ)=490, F2(ɔ)=1000 (I kept the other parameters at their default values). However, the F2 values that I used do not correspond to the typical F2 values one finds in the literature for those vowels. For instance, Gendrot and Adda-Decker (2005) found F2 values of about 1000 Hz and 1200 Hz for [o] and [ɔ], respectively. But, with these values, the vowels sound too central to my ear.
Any idea of why that might be so? And also, does anyone know of another (free) software that I could use to synthesize French vowels with realistic formant values?