It's loungy, jazzy, and only a little bit sad. Louis Armstrong's trumpet sings plaintively, as if it's a voice in a duet with Bessie Smith's raspy beauty. A goofy harmonium gently taps out chords in a church-style dirge behind them both. In four brief strains, "St. Louis Blues" comes and goes as easy as elevator music. It's hardly the hard, heart-breaking stuff we associate with the old-time blues.
And yet, in form and in content, "St. Louis Blues" is definitely blues. It's longer than a traditional blues—the most basic blues are 12-bar progressions, which might be repeated several times. This one is written in 52 total measures, with the first two verses repeating in basic 12-bar form. The third verse is in 16 bars coupled with a subtle shift to a minor key and a tango beat, and the fourth concludes in 12 bars that differ only slightly from the first two. Altogether, the song follows an AABC form, with the tango-like B section serving as a bridge to the somewhat cheery conclusion. It's admittedly an unusual progression for a blues song taken altogether. Within each verse, however, the structure of the blues is present: the first two lines are repeated, followed by a conclusively sad and drifting third line, and the A and C sections also follow the bluesy 12-bar structure starting and ending on the major tonic chord after ambling through a I-IV-V chord progression sprinkled with blues scales. And Smith hits the classic blue notes (the notes in blues where the singer is intentionally flat to create a blue feeling) from the very first line, where "sun" is written as a B flat and sung with a falling sadness Bessie had total mastery over.
It may seem a little eclectic next to the simplicity of 12-bar blues, but the little extravagances of "St. Louis Blues" were part of the appeal. It's a compact, lovely little blues, maybe a little upbeat for purists, but perfect for the jazz-blues crossover and pop/easy listening crowds. W.C. Handy got a little flashy, but the effect ultimately stayed simple: "Handy threw anything he could think of—every aspect of African-American vernacular music—into 'The St. Louis Blues.' As we've seen, it is a genuine blues, using blues form, blues harmony, and blue notes," writes Friedwald (Stardust Melodies: A Biography of Twelve of America's Most Popular Songs, 49).
The only problem, according to Friedwald—and we might have to agree with him here—is in the instrumentation on the Smith and Armstrong collaboration. He writes: "One has to question the decision (presumably by producer Frank Walker) to back this duo with a Martian-sounding, organ-like keyboard known as the harmonium" (66). To be fair, they probably didn't know about Martians back then.