Subjective impressions of speech delivery in Autism Spectrum Disorder (ASD) as monotonic or over-precise are widespread but still lack robust acoustic evidence. This study provides a detailed acoustic characterization of the specificities of speech in individuals with ASD using an extensive sample of speech data, from the production of narratives and from spontaneous conversation. Syllable-level analyses (30,843 tokens in total) were performed on audio recordings from two sub-tasks of the Autism Diagnostic Observation Schedule from 20 adults with ASD and 20 pairwise matched neuro-typical adults, providing acoustic measures of fundamental frequency, jitter, shimmer and the first three formants. The results suggest that participants with ASD display a greater articulatory stability in vowel production than neuro-typical participants, both in phonation and articulatory gestures.