FM Stereo broadcasting was approved by the FCC on April 20, 1961. Yet I found an interesting way local radio stations were attempting to take advantage of just that sound prior to that date.
Both WOSU AM and FM as well as WBNS AM an FM began stereophonic broadcasts on a regular basis in 1957. But instead of using one band, they used both their AM and FM frequencies to make up the broadcasts.
WOSU had experimented with the process for about a year before beginning a regular schedule. WBNS would just begin, as their FM had returned to the air after a 4 year period of silence on Thanksgiving Day, 1957.
WOSU did their daily broadcasts in the afternoons between 4:30 and 5:30 pm. WBNS waited until the end of the day to do theirs which was between midnight and 1 am. Oddly at a time when the WBNS AM signal would suffer night time ingress from other stations as well as their reduced power and directional signal.
High and low end audio frequencies were split between the bands. The FM signal would carry the lows while the AM signal focused on the highs.
