Sending audio over infrared?
That was - early in the history of LEDs - pretty common, even without the PWM stage. Depending upon the angle of the IRLED, you can get a VERY long distance out of one... but aiming gets rapidly more difficult with longer distances. A very carefully aimed IRLED with a very narrow beam can transmit audio reliably over several miles in clear weather.

The greater the distance, though, the greater the likelihood of incidental noise from reflection, refraction, and air movement.

The old Popular Electronics magazine published several articles long ago about transmitting unmodulated audio with IRLEDs. Back then, LED beam angles were nearly all pretty broad, so theirs required focusing/collimating lenses. Today, you can easily find IR laser LEDs so there's little need for collimating lenses except arguably at the photodetector end.