Old is new on radio. If that sounds interesting and slightly paradoxical, it is a strategy that some private FM stations have adopted. Retro is clearly the new thing with Bollywood music starting from the 1960s to the 90s getting some serious airtime. Of the nine FM stations in Mumbai, three play only retro music, in what is turning out to be a very interesting battle for a share of the Rs.225 crore radio advertising pie in the city.