Good dance music always sounds so easy to do. But as the four dance bands at Capital Centre proved last night, it's harder than it seems. All the groups found that the right combination of personal vocals, catchy riffs, syncopated rhythms and strong songwriting is elusive.

The 10 members of L. T. D. obviously set out to imitate the look and sound of the Commodores and Earth, Wind and Fire. But last night L.T.D. relied heavily on chanted vocals, lock-step rhythms and unison chording. This prevented the harmonies and textures that make their models worth imitiating.

Larry Graham pioneered the slap and snap technique of bass playing while part of Sly & The Family Stone. Graham is still a superlative bass and a solid singer as the leader of Graham Central Station. But last night he desperately needed Stone's songwriting skills. For example, Graham's new single, "Sneaky Freak," had a top notch dance beat but no melody worth remembering.

The songwriting team of Gene McFadden and John Whitehead has turned out danceable soul hits in the Philadelphia style for several years now. Their own big hit, "Ain't No Stopping Us Now," has moved from behind the scenes to front stage. But last night their voices proved thin in tone and narrow in range. They shouted and danced through their hit, but the melody had to be carried by the horns and backing female singers.

The Gap Bank opened with a set of forgettable funk.