"For his first date, Trumbauer came up with a pair of classic performances. Singin' the Blues left an impression on virtually every saxophone and trumpet player and, with the exception of Louis Armstrong's West End Blues, has probably been more widely copied than any jazz performance recorded in the twenties. With this record, a legitimate jazz ballad style was announced--a method whereby attractive songs could be played sweetly without losing authentic jazz feeling and without sacrificing virility. Prior to Singin' the Blues, "pretty" tunes were either cloyingly sentimental or cranked up to an awkward jogging pace. Jazzmen generally played the blues or blues songs when slow tunes were called for. Bix Beiderbecke, with the help of the electric microphone (which permitted an intimate performance by singers and instrumentalists, on the stage or in the recording studio, for the first time), changed the pattern almost single-handedly. Trumbauer, who at best was a bright reflection of Beiderbecke, contributed substantially by proving that the ballad idea wasn't a one- man phenomenon but a workable way for anyone to play certain song material.
"It is reasonable to assume that Bix's concept of playing a ballad in moderate 4/4 tempo came, at least in part, from his passion for romantic and impressionistic melodies in formal music. His ear for harmony, too, meant that Bix could hear enough alternate chords within each measure of a popular song to sustain his improvisations at a slow pace. Singin' the Blues may not seem very slow by today's ballad standards, but in 1927 it was about as slow as anyone dared to be without strings and sweet arrangements." Jazz Masters of the Twenties , p.89-90 https://archive.org/stream/jazzmastersofthe006082mbp#page/n89/mode/2up/