It's funny the way one musician can change the entire sound of a jazz band. Last week, before the official opening of Steve Connelly's Rathskeller, a trumpeter named Shad Collins was playing with the Vic Dickenson-Buster Bailey outfit in the little cellar in back of the Bradford. Little Shad is a former Basie star, but his playing, strangely enough, was straight from the Delta, and the group had the most authentic New Orleans sound heard in Boston for some time.

Now one Jimmy McPartland has brought his cornet out of the west (by way of Europe and Canada) and overnight the Rathskeller band is as Chicagoan as the Outer Drive.

The reason may lie in a submerging of ensemble work and increase of soles--one subtle difference between Crescent and Windy City styles. More probably, however, it is the very versatility of the house musicians.

Dickenson and Bailey have been around for a long time. Trombonist Vic has developed his taste and feeling over more than a quarter-century of playing with the best in the field, and Buster has been a clarinet wizard to generations of greats and near-greats. Bailey is a grandfather now, but he can still blow a chorus that sounds as if it were some- where between Goodman and Ed Hall--with the smoothness of neither, but the imagination of both.

Of McPartland Bix Beiderbecke once said, "He's the greatest white trumpet man in the world." Most of the Bixian refrain has gone from McPartland's horn now, and he has become more of a New York-dixicland musician. But, like Bix and unlike almost all others, he doesn't startle you with his music; he just plays it "awfully pretty" in a quiet way.

The Rathskeller features fine acoustics in a genuine upholstered celler--painted walls, exposed pipes and girders, and kitchen chairs. If places like this keep open, Boston will soon have a wider selection of quality jazz than either New York or Chicago.