"radio, which transmits over EMR but encodes audio frequencies" Radio conveys all sorts of things, not just audio. They're orthogonal issues. And you actually

"radio, which transmits over EMR but encodes audio frequencies" Radio conveys all sorts of things, not just audio. They're orthogonal issues. And you actually could modulate 20khz BW of audio onto a 30khz carrier using SSB-AM for example. That carrier could be EM, a voltage in a wire or an ultrasonic tone. Not that it's relevant to the issue but it does reinforce the point that the nature of the medium is independent from the intelligence being conveyed. There is no correspondence. Sonics/audio are pressure waves and do not belong on the EM spectrum.