Singing Power Ratio (SPR) is the ratio between the highest intensity peak from the 2-4 KHz range and that from the 0-2 KHz range. The SPR analysis of human voice has been found useful for gauging a singer’s “formant tuning” technique, a technique useful for projecting voice over the orchestra sound energy, which is often found lower around the 3 kHz frequency region. To assess how different pitch levels, vowels, and musical instruments may pose different levels of demand on “formant tuning”, this study compared the vowel production (/i, e, a, o, u/) of a trained singer with notes played by a selection of commonly used musical instruments. The musical instruments included: wood wind (flute, oboe), brass (trumpet), string (violin, cello, guitar), and keyboard (piano). Eighteen notes, from C4 to F5, were obtained from each instrument. The energy of each recorded signal was normalized. A 300-ms segment taken from the middle section of a note was submitted to spectral analysis to yield SPR and other timbre-related spectral measures. One-way Repeated Measures Analysis of Variances were performed. The SPR values for wood wind, brass, keyboard, and back vowels (/a, o, u/) were found to be the lowest, followed in order by string and front vowels (/i, e/), indicating that front vowels might have the advantage of being heard over most musical instruments. The SPR values were found to be independent of pitch for all musical instruments except for violin, which showed a positive relationship between SPR and pitch. For the high vowels (/i, u/), SPR decreased as pitch increased, suggesting that these vowels might demand more “formant tuning” for projection as the target pitch is raised.