> The interesting thing with this example in particular is that the audio output from the radio is already very well-gated thanks to an RF squelch

Author here. Luckily for my purposes I can rely on the radio already having a squelch, so I could get away with using the naive solution.

If it was the raw audio I'd probably need to implement something more sophisticated such as splitting the audio by frequency and giving each band a noise threshold (as atoav mentioned).