Those recordings of blues singers from before WWII were made when singers had to shout to be heard--in performance venues and in recordings. The 40's were the first time, near as I can tell, when popular-music singers learned how to use the microphone and amplification, and that changed the way they expressed themselves.
The instruments were altered for recordings, too. The tubas used in Dixieland music were usually sousaphones, but with a forward-facing bell. Most people think sousaphones were invented that way, so ubiquitous as the forward-facing bell has been with that configuration. But the original sousaphone had a bell that faced straight up, like a concert tuba. But when recordings were being made starting in the 20's, the bells pointed up couldn't be heard by the one microphone out in front of the group, so the instruments were designed with forward-facing bells for both sousaphones and for lap tubas. In fact, one standard term for a lap tuba with a forward-facing bell is "recording bass". (Tubas were commonly known as "bass horns" in American usage in those days, too, and even right up into my school years. Most published parts for tubas printer prior to about 1975 or 1980 say "Basses" at the top.) I say that to emphasize the need for instruments to be loud to get into the low-sensitivity recording processes of those days.
Rick "apparently, not the only tuba player in this conversation" Denney
The instruments were altered for recordings, too. The tubas used in Dixieland music were usually sousaphones, but with a forward-facing bell. Most people think sousaphones were invented that way, so ubiquitous as the forward-facing bell has been with that configuration. But the original sousaphone had a bell that faced straight up, like a concert tuba. But when recordings were being made starting in the 20's, the bells pointed up couldn't be heard by the one microphone out in front of the group, so the instruments were designed with forward-facing bells for both sousaphones and for lap tubas. In fact, one standard term for a lap tuba with a forward-facing bell is "recording bass". (Tubas were commonly known as "bass horns" in American usage in those days, too, and even right up into my school years. Most published parts for tubas printer prior to about 1975 or 1980 say "Basses" at the top.) I say that to emphasize the need for instruments to be loud to get into the low-sensitivity recording processes of those days.
Rick "apparently, not the only tuba player in this conversation" Denney