It's to provide "comfort noise" when the correlator indicates a missing or mistuned signal.

Muting the audio would make more sense -- and would certainly have been familiar to the CB[1] radio operators of the day in the form of a squelch effect -- but this chip was targeted at consumers who expected it to behave like a conventional FM radio.

1: An early incarnation of social media, for better and worse

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wkat4242 3 days ago | parent [-]

Haha yes I know CB radio. I used it for many years and I'm still a ham. It was a lot like social media yes. Never thought of it that way. Also, BBS'es. And the combination thereof which was packet radio.

But I didn't think of this because it's an analog receiver. I thought it would just receive noise in the absence of a signal like its older brethren did.

	▲	CamperBob2 3 days ago \| parent [-]
		You would hear the usual white noise between stations, just by virtue of FM reception relying on high IF gain ahead of a limiting stage. But judging from the description of the block diagram, I suspect the noise you'd hear when tuning in a station would be very unfamiliar, maybe a lot of distorted tones and whistles. I can't believe they'd have gone to so much trouble to hide it otherwise. It's a much more interesting chip than it initially appeared to be, that's for sure.