The impact of rock's aversion to understatement has been so pernicious that even so dynamic a performer as singer-songwriter Melissa Manchester is persuaded to engulf her impressive vocal gifts in a tidal-wave roar of electronics.

Yet amid the din and thud last night at Merriweather Post Pavilion were some quiet spaces in which Manchester's warm timbre and her nuances of expression were evident. In particular there was a number for which she sat beneath a pin spotlight on a conga drum and sang to the solitary accompaniment of an acoustic guitar. It was an eloquent rebuttal of the humongous-is-better bias of contemporary pop entertainment.

Manchester has an entire cast of faces to match the moods of her songs--pouting, saucer-eyed amazement, raised-eyebrow shock and clenched-teeth anger. Her smile is pure Norman Rockwell Girl Next Door and a whirling dervish would be hard put to keep up with her sweeps across the stage.

In spite of the muddled sound and superfluous volume of her six-piece band with two backup singers, Manchester brought off several of her originals and a Gershwin medley with admirable flair and an energy that could split the atom.