International audience The first two vocal tract resonances (R1 and R2) of 22 classically trained sopranos, altos, tenors, and baritones were measured while they sang four different vowels over their normal pitch range. The resonances of the tract and the harmonics of the voice were measured simultaneously by injecting a broadband acoustic current into the tract at their mouth. Sopranos were found to tune R1 close to the fundamental frequency f0 (R1:f0 tuning) over at least part of their upper range for all vowels studied, particularly when f0 was around or above the value of R1 for speech. Additionally, most sopranos employed R2:2f0 tuning over some of their range, often simultaneously with R1:f0 tuning. Altos used R1:f0 tuning for vowels having lower values of R1 in speech, but can switch to R1:2f0 tuning in the lower part of their range. Tenors and baritones generally used R1:2f0 and R1:3f0 tunings over part of their range and employed a number of different tunings to higher harmonics at lower pitch. These results indicate that singers can repeatedly tune their resonances with precision, and that there can be considerable differences in the resonance strategies used by individual singers, particularly for voices in the lower ranges.