It is like a secret society. If you want to attend a Morning Musicales performance, first you have to find it. The classical concerts are, sadly, no longer held in the Academy of Music's newly restored ballroom but at the Curtis Institute of Music's Field Concert Hall.

Note the name: Concerts start at an unusual time - 11 a.m. The series is a project of the West Philadelphia Committee of Philadelphia Orchestra volunteers - a melodious misnomer that really means the suburbs to the northwest of the city. And good luck finding these concerts on the orchestra's website.

The Morning Musicales program has often called upon the curatorial wisdom of Astral Artists, from whose roster Thursday morning appeared mezzo Chrystal E. Williams in a recital of such artistic scope as to belie its mere one-hour duration.

Williams, an Academy of Vocal arts alumna, responded with great plasticity - of sound, stylistic treatment, of emotion. She is a singer of rare power and clarity.

With pianist Laura Ward evoking orchestral sound in four movements from Berlioz's Les nuits d'été, Williams beautifully controlled the balance between delicacy and digging deep down for drama. Parts of this piece leave singers exposed, and Williams made easy work of both moments that required coming in out of nowhere, as well as sneaking in with velvety sound.

There is a certain raw, unguarded color some singers find in Falla's Siete canciones populares Españolas, and Williams inched right up to it.

The spirituals that ended the recital were, of course, as the material demands, a release of sorts, freeing up the singer to tell us in bold letters how she feels.

But the real stunner of the morning was John Musto's Shadow of the Blues, with its Langston Hughes text and unfailingly moving - and not always intuitive - text painting.

Musto takes "the sick, the depraved, the desperate, the tired, all the scum of our weary city," and gives them dignity. His is a purely American vernacular sound, but it's neither falsely sentimental nor afraid to tell the truth. It was here - in the reassurance of Ward's flowing river and Williams' sensitive inflections - that you could hear America in all of its complexity and contradiction.