Cissy Houston is one of the greatest singers in America, but to many people she's either Cissy Who?-ston or Whitney's mom. In David Davidson's documentary "Cissy Houston: Sweet Inspiration" (tonight at 10 on Channels 26 and 32), Whitney says, "I am from her," and she means not only as a daughter, but as a singer.

Although she's had success as a performer -- as one of the most sought-after session singers ever, as leader of the Sweet Inspirations and as a solo artist -- Cissy Houston has also been a great teacher, not only to her daughter but to the hundreds of singers who have come and gone in her Radio Choir at Newark's New Hope Baptist Church.

It's there that Houston trains people "to sing out their feelings in their own way." Luther Vandross, whose career has certain parallels and who is an aficionado of the great singers, considers Houston the greatest, not only because of her astounding voice and technique, but because "she makes the people around her want to sing their best."

Davidson's film follows an evolution common to many of the great singers: from classic gospel roots to the divergence of rhythm and blues and soul. As Atlantic Records producer Jerry Wexler points out, there are many similarities between gospel and soul, so for many black artists in the early '60s, singing soul was "like going home."

Houston and her three sisters started out performing gospel in the early '50s as the Drinkard Singers, who achieved some national recognition at the 1957 Newport Jazz Festival (there's a delightful living room sequence of her sisters singing today, showing they've lost none of their fervor). Houston got into pop music almost accidentally, filling in during a recording session for her ailing niece Dionne Warwick. It was a financially rewarding expansion, and, for 25 years now, she has "sung both sides."

That duality, which has caused some problems in church circles, is evident in various performance clips (including a Sweet Inspirations reunion concert), but Houston's preference for gospel is clear. On the secular side, she can be both exuberant and evocative; but on the spiritual side, she's always exalted, and no more so than when she's enveloped by the community of singers in her choir. "Music is a way for black people to communicate with God," she says. "There are times when you can't do anything but sing."

Watching Houston rehearse the choir, one can see she's a tough teacher, as apt to reprimand as to encourage (her title at the church is "minister of music"). But one senses that she produces not just better singers, but better people. Listening to the praises from Vandross, Warwick and Aretha Franklin, and from producers Wexler, Tom Dowd and Arif Mardin, it's obvious that she's much admired, but the real proof comes musically. In one segment, Cissy, Whitney and her son Gary Garland Houston turn a song from "Dreamgirls" into a vibrant family tableau.

Even better is the film's final sequence, a church performance in which Houston and the choir address the joy of "When I Get to Heaven" with the simplest of techniques: giving everything, every time. In that joyful, sweat- and tear-fueled exhaustion, one encounters not only the power of faith and the strength of the black church, but also the grace of a remarkable person.