The jazz vocalist rhiannon (she prefers the lower-case spelling) is best known for her work with the all-women jazz ensemble Alive! Though still a member of the quintet, she's currently on hiatus, touring with guitarist Mimi Fox. Last night, the pair performed at Blues Alley and the results were mixed.

Because Fox often plays an acoustic guitar and favors a sharply percussive attack, much of the music they performed possessed a folkish flavor, despite the improvisational bent of both musicians. Rhiannon's strong, slightly tart voice would dart between Fox's three-octave runs or soar above them in extemporaneous flight. One couldn't help but be impressed by rhiannon's technique or her resourcefulness in imitating exotic tones and effects. But too often these breathlessly scatted passages only recalled more expressive vocalists in the field -- Betty Carter, for one -- and ultimately seemed shallow by comparison.

Not everything was so hurried or strenuously sung, however. A warm, lovely and precisely controlled revision of "My Funny Valentine" displayed rhiannon's talent to its fullest. Another refreshingly uncomplicated moment came later when Fox picked up a hollow-body electric guitar and offered a beautiful bell-toned version "All the Things You Are."