|Bing Crosby and microphone|
The microphone, like all successful new technology, had a profound impact on life and culture, including the development of entire new industries. It affected music in numerous ways. For one, it enabled the development of an entirely new approach to singing popular songs.
Before the microphone came along, people singing in public had to develop a technique of vocal production that could make their voices heard in the farthest corner of the largest venues. Opera singers were the first to require it, but they were not alone. Singers of American popular music did not need a voice suitable for opera, but they did need a big voice and forceful delivery. Listen to this 1928 video of Al Jolson singing “It All Depends on You,” and especially watch his posture as he concludes the song. It appears to be not only a dramatic gesture, but a means of adding sheer power to the finish.
Of course, Jolson could not have recorded that clip or anything else without a microphone, but as long as microphones were used only for recording, no one could sing in a theater, dance hall, or otherwise large venue without developing a comparable vocal technique. Only when it became available for live performance could professional singers use a softer, more intimate style.
Rudy Vallee appears to have been the first major star to use a microphone to sing in a ballroom, in 1930. Although it is uncertain how rapidly the sort of sound system he used became commonplace, others in the business surely noticed. Listen to this 1934 recording of Bing Crosby singing “The Very Thought of You.” The microphone picks up the slightest sound of his voice. If he sang that way unaided in a large hall, no one would have been able to hear him. The microphone enabled a gentler, more intimate delivery in public that before would have been suitable only in the privacy of someone’s house.