The planet Miller is close enough to the black hole to be affected by relativity, so that one hour on the surface is equivalent to 7 years in the real world. Earth has received a signal from Miller saying the planet is hospitable for human life, but it turns out that Dr. Miller died shortly after arriving and the message has been repeating.
But my understanding of relativity would suggest that the signal would be enormously speeded up when received in the real world because of time dilation. Instead of being a radio signal the frequency would be over 60,000 times higher (24 hours * 365 days * 7 years = 61320). If we assume they're using the Ka band then a 23 GHz signal would end up as 375 KHz, in the medium frequency radio range.
Update: Hypnosifl pointed out I'd got this the wrong way round.