Soft AC, as defined going back to the WDUV success story, is basically very light on recurrents, few currents and consists of mostly gold that is not rock, dance, urban or country. In its earliest form, it was Barry Manilow and the Carpenters with a dash of John Denver.
Today, "soft" AC is less soft and more gold based, but without the nostalgia of pure gold and the inclusion of some currrents and recurrents.
AC began as "chicken rock" and was Top 40 without the harder rock but with more adult ballads. That began around '71 or '72 and, of course, had lots of gold mixed in. In more recent years, some AC stations started playing more currents, becoming Hot ACs and some reduced the currents and some of the "hottest" stuff while playing older gold and became Soft AC.
Adult hits, or the "Jack" format, can be more rock driven in rock-partisan markets, and much less in more rhythmic or AC driven markets. In fact, the Jack stations in the top 50 markets all have locally determined playlists.
