Citizen Kane

In Citizen Kane, music is mainly used to advance transitions and make montages flow. In the beginning of the film, a somber theme using low, quiet brass and strings as the camera slowly moves from the outside of the Xanadu fence at a low angle to the inside of Kane's room as he says his final, famous word: "Rosebud." This theme gives Kane's estate a funereal air and also surrounds Kane's death with a certain mystery because the visuals show that he is very alone at the end. This relatively quiet music sets up a great contrast with the boisterous trumpets and drums that briefly introduce "News on the March" which uses a histrionic narrator to quickly highlight the highlights of Kane's public life. During "News on the March" this narrator is accompanied by a full orchestra and brief videos of Kane meeting important leaders, acquiring wealth, etc.
Later, 5 separate short scenes compose a montage of Kane and his first wife. Their relationship in the first is one of love and gentle nagging toward Kane to spend more time at home, and he's jocund and somewhat willing. At this point, the music involves mainly strings and is soft, nearly romantic. The next is mostly woodwind and strings, somewhat gentle yet as Mrs. Kane is still gently prodding Kane to spend less time at the office. The music is sinking woodwind and some brass as she sadly tells Kane he shouldn't directly attack the president so brazenly. The penultimate is somewhat lower brass and Kane directly orders Mrs. Kane to continue to allow the coarse Mr. Bernstein in the nursery with their son. In the final scene, the strings reappear much sadder as Mrs. Kane dejectedly scolds Kane for his dishonest paper, and Kane vehemently tells her "People will think what I tell them to think!"
Some less noticeable music, usually underscoring, is used in the flashback scenes, and in general the film uses its score as a means of highlighting and characterizing segues.
It is also worth noting that imdb.com refers to six composers, including Max Steiner, as sources for stock music used throughout Citizen Kane.

Double Indemnity (Rózsa)

In Double Indemnity, Rózsa begins with music only when the narrator is talking and the scene is changing, improving the transition between the flashback scenes and the present narrator recording the whole story. After Walter Neff, who is also the man recording the story in the present, agrees to help Phyllis kill her husband, a turning point in the movie, Rózsa begins to employ music in the increasing emotional scenes inbetween narrative explanations.

The music associated with the narration enhances the continuity of the film, employing a similar sequence of notes throughout the film. In general, this is background underscoring, mostly strings that are practically a much slower version of those used in Psycho. Combined with the sober tone of Neff's narrations, this theme evokes mystery and suspense without becoming obnoxious. As Neff narrates that his hands shook uncontrollably at work after killing Mr. Diedrickson, the music seems to fade out before the narrator is completely finished perhaps to highlight Neff's anxiety in the flashback that something is out of place.

After the first time Phyllis comes to Neff's apartment, Rózsa begins coupling music with some of the flashback dialogue to illustrate emotions or tension. For example, a mildly romantic violin piece overshadows the other, more subdued instruments as Phyllis and Neff kiss in his apartment shortly after tacitly agreeing to murder Mr. Diedrickson. As Neff is preparing for the killing, a brass sequence similar to the string sequence becomes the main sound. This continues, intermittenly joined by strings, until Neff, Phyllis, and Mr. Diedrickson turn down a dark side street. The camera then focuses on Phyllis in the driver's seat as a brass crescendo and subsequent pause clearly illustrate that Neff has strangled or otherwise killed Mr. Diedrickson. When Neff goes to Phyllis' house to privately interrogate her, he enters her house and hears the diagetic radio of a neighbor. It is some sort of unobtrusive trumpet instrumental. After they talk heatedly, he closes the window, shutting out the diagetic music and increasing the tension between the two characters, both armed, in a dark room with no music. Phyllis then shoots him and then stringed underscoring returns.

The Sea Hawks (1940)

Throughout The Sea Hawk, bold, underscored trumpets accompany the Sea Hawks while they are at battle on the sea, concurring with and foreshadowing their apparent invincibility while at sea. These trumpets first break out happily as an unlikely cannonball fired from the Albatross shatters the flagpole of the antagonistic Spaniard ship. They are not always constant during battles, but are especially noticeable during strategic successes such as the freeing of the enslaved rowers (the first time), boarding of the ship, and the transport of their new loot. The biased trumpets help the viewer join the Sea Hawks in their atmosphere of triumph and exhilaration. In contrast, the trumpet used with the Sea Hawks' capture of the Spanish gold is not as bold, signalling that the previous battles were more difficult and thus more glorious and also warning us that this victory may be short lived.
The trumpet is also foregone in some instances to fit a more subdued emotional atmosphere. For instance, while Captain Thorpe and his crew make their incredibly brave escape from chains as enslaved oarmen, they do so quietly enough not to wake up the guard. Korngold substitutes quieter strings in the escape scene to accentuate the whispering of Thorpe and his comrades. There is a brief crescendo of strings and low brass used to support the silent strangling of the timekeeper and killing of various guards, which is also silent. This is far more suspenseful and natural than loud trumpets that signify sure victory but are too loud for the stealthy scene. The trumpet makes its logical return when the Sea Hawks have sure control of the ship and lower the sails.