Read the following paragraph and extract the answer for the question: What is the name of the solo work that is an important example of the "jazz ballad style"?

In New Orleans, jazz had traditionally been expressed through polyphonic ensemble playing, with the various instruments weaving their parts into a single and coherent aural tapestry. By the early 1920s, developments in jazz saw the rise of the jazz soloist, with solos becoming longer and more complex. Both Beiderbecke and Armstrong were key figures in this evolution, as can be heard on their earliest recordings. According to the critic Terry Teachout, they are "the two most influential figures in the early history of jazz" and "the twin lines of descent from which most of today's jazz can be traced."Beiderbecke's cornet style is often described by contrasting it with Armstrong's markedly different approach. Armstrong was a virtuoso on his instrument, and his solos often took advantage of that fact. Beiderbecke was largely, although not completely, self-taught, and the constraints imposed by that fact were evident in his music. While Armstrong often soared into the upper register, Beiderbecke stayed in the middle range, more interested in exploring the melody and harmonies than in dazzling the audience. Armstrong often emphasized the performance aspect of his playing, while Beiderbecke tended to stare at his feet while playing, uninterested in personally engaging his listeners. Armstrong was deeply influenced by the blues, while Beiderbecke was influenced as much by modernist composers such as Debussy and Ravel as by his fellow jazzmen.Beiderbecke's most famous solo was on "Singin' the Blues", recorded February 4, 1927. It has been hailed as an important example of the "jazz ballad style"—"a slow or medium-tempo piece played gently and sweetly, but not cloyingly, with no loss of muscle." The tune's laid-back emotions hinted at what would become, in the 1950s, the cool jazz style, personified by Chet Baker and Bill Evans. More than that, though, "Singin' the Blues" has been noted for the way its improvisations feel less improvised than composed, with each phrase building on the last in a logical fashion. Benny...
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Singin' the Blues
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