Working in secret in the basement laboratory of Columbia's Philosophy Hall, Armstrong developed "wide-band" FM, in the process discovering significant advantages over the earlier "narrow-band" FM transmissions. In a "wide-band" FM system, the deviations of the carrier frequency are made to be much larger in magnitude than the frequency of the audio signal; this can be shown to provide better noise rejection. He was granted five US patents covering the basic features of new system on December 26, 1933. Initially, the primary claim was that his FM system was effective at filtering out the noise produced in receivers by vacuum tubes.