In case there is any doubt just what a conductor is good for, Columbia has released a fascinating and informative album called The Birth of a Performance. The music is Mozart's "Linz" Symphony (No. 36) and the star is Conductor Bruno Walter, 79. Three of the four sides are devoted to rehearsal (the fourth is the finished performance), with Walter's kindly voice correcting, explaining, singing (off key), completely unaware that he is being recorded.
Unlike tempestuous Arturo Toscanini, Walter does not frighten musicians into playing right; he coaxes them. When, with his mellow German...