In 1949, RCA victor introduced Extended Play (EP) discs that had a speed of 45 rpm and were 7 inches in diameter, making them easily stackable in jukeboxes. Because you would have to buy two types of record player to play both LP's and EP's, customers held back to see which one would dominate.
Before 1947, sound quality of recordings were quite poor and discs could only hold 5 minutes of sound per side. In 1947 Columbia Records introduced the LP (Long Playing) 33 1/2 rpm disc that held 23 minutes of audio per side. However, you needed an LP adaptor to play these.
Although microphones were originally designed for use in telephones, at this time, they started to become popular in recording studios, allowing the singer to be heard over the rest of the band and so working a prominent place in popular music.
The depression during this decade saw the recording industry struggle because radio had superior sound quality and consequently record sales fell. However, during the 1930's records began to be played more on Radio stations and the recording industry thrived again.