The first scene Clint Eastwood shot was his former director Don Siegel's cameo as Murph the bartender. As a joke, Eastwood made Siegel do 11 takes - then told the cameraman to put the film in the camera.
When Clint Eastwood told Universal executive Lew Wasserman that he wanted to direct the film, Wasserman agreed immediately. Then, as Eastwood and his agent were walking down the hall, Wasserman called the agent back into his office. In exchange for letting Eastwood direct, they wanted to pay him less than his regular salary under his three picture deal. Eastwood understood, given that he was a first-time director. In the end, he made the movie for a percentage of the gross.
In one of the film's early scenes, Al Monte is heard telling his listeners that the Monterey Jazz Festival is four months away. Based on the events that unfold, that would mean that the film covers a time span of slightly over four months.
The documentary I'm Your Number One Fan (1996), which was about celebrity stalkers, had a segment which was similar to the plot of this film: a woman called Blue Tulip Rose Read, who was obsessed with DJ MIke Read. She claimed to be married to him, and even dressed like him. The documentary shows Blue Tulip Rose Read going to the radio station where Mike works, hoping to meet him and get him to marry her, but security stops and ejects her.
The story line was originally set in Los Angeles, but at Clint Eastwood's insistence, the film was shot in the more comfortable surroundings of Carmel-by-the-Sea, where he could shoot scenes at the local radio station, bars and restaurants, and acquaintances' houses.
Jessica Walter has contributed to multiple documentaries about Clint Eastwood in which she praises him enthusiastically. However, Sondra Locke notes in her autobiography that when she met Jessica at a party in the early '70s right after this film was made, "she spoke in measured tones about Clint, and I got the distinct impression that she did not view him as a very generous actor or human being for that matter."
Clint Eastwood obtained the rights to the song "Misty" after he saw Erroll Garner perform at the Concord Music Festival in 1970. Eastwood also paid 2,000 dollars for the use of the song "The First Time Ever I Saw Your Face" by Roberta Flack.
The idea of another love interest, with a level-headed girlfriend Tobie added to the plot, was a suggestion by Sonia Chernus, an editor who had been with Clint Eastwood when he was initially spotted for Rawhide (1959).
The film features a romantic montage (views of Garver and Tobie peacefully roaming by the seaside and through the woods), backed by Robert Flack's recording, an Ewan MacColl torch song. Flack's version (after staying at number one for six weeks during the spring) became the 1972 Billboard Hot 100 top single of the year.
The radio station, KRML, was an actual jazz station in Carmel, whose studios were relocated to the Eastwood Building at San Carlos and 5th, in the same building as the Hog's Breath Inn (a restaurant that Clint Eastwood co-owned). After a brief dark period in 2010, the radio station returned to the air in 2011.