One of the major influences on recorded music in the 1930s and 1940s was related to the refinement of electrical recording processes. Since microphones could be placed anywhere, even inside an instrument like the piano, it was no longer necessary for musicians to crowd around a single spot in order to be heard. In fact, once engineers began experimenting with the use of multiple microphones, they could record a whole symphony orchestra, even if they were spread out across a large stage. However, the use of more than two or three microphones remained rare.

Another thing that was possible with multiple microphones was electronic mixing. After “miking” a singer and a band with two separate microphones, a recording engineer could adjust the level of each to create a pleasing sound. It was possible, though apparently not common, to adjust these levels in the midst of a recording session, so that for example a short solo could be emphasized over the background playing. Music historians are not sure what to make of all this. On the one hand, the continual improvement of electrical recording technologies resulted in the possibility of greater fidelity to the original performance. On the other hand, techniques such as mixing multiple microphones led to recordings that sounded less and less like the original performance, even though the were very pleasing. This contradiction is as true today as it was then.