Who created the audio experience? Kazuki Muraoka. It's hard to find out much about him, although he does have at least one interview where he talks about his work on the Metal Gear series. I didn't play any of those games, so Contra was my encounter with his work. For the NES version, there's also a track that plays during the introduction (story) to the game which was composed by Hidenori Maezawa and Kiyohiro Sada.
One thing I'm realizing as I investigate more of these games is that there's not enough clear distinction between the various jobs that people had in games. Sound producer, composer, sound programmer, arranger, etc... although one person may do more than one of these tasks, these jobs are all different! Contra was first an arcade game and then ported over to the NES. (Here also is a link to a video that shows the cutscenes as well as the gameplay) The music is virtually the same in both versions, although arcades had better audio capabilities than the NES did, so there was definitely a bit of simplification as well as re-programming that had to take place between the two mediums. If you check out the wikipedia page for Contra, it lists the Kazuki Muraoka as the composer of the arcade version and Hidenori Maezawa and Kiyohiro Sada as composers for the NES version. Since the music is the same from the previous arcade version to the NES version (except for the introductory track) something's not right here... Perhaps it's a matter of semantic confusion, but a person who writes music is a composer. If those tunes are altered, modified for a different ensemble (in gaming, this might be considered as moving between platforms), or even to a certain extent reimagined, they aren't "composed" by someone new. They've been arranged. Thus, Kazuki Muraoka composed all the music except for the introductory track, which was written by Hidenori Maezawa and Kiyohiro Sada.
I'm starting to see some advantages that OverClockedRemix and vgmpf.com have over the main Wiki for game music. The information is more correct with greater specificity of appropriate musical terms. However, I've got to completely disagree with vgmpf's "Regardless of who worked on the music, it's a pretty impressive soundtrack" toss away on the Contra page. It's important to know exactly who created the music!
What is the audio experience? Numerous sound effects for shooting and blowing things up, of course. There's different music for each level of gameplay, boss battles, and various end game musics. I'm realizing now that many games have more music toward them of the game that I didn't hear very often because I'd often die before making it that far. There's almost an acceleration of new themes toward the end of a game, with the final level, boss battle, and end game music (I'm thinking here of Mega Man in addition to Contra here). Hearing the music at the end of the game is almost a reward for making it so far through the game. Overall, the music has a rock and roll, techno sort of sound.
How does the audio experience draw the player more deeply into the game? The reusing of themes, for instance, the interior "3D" scenes lends a unity to those scenes of gameplay. I don't get the Jungle/Hangar theme connection, although reusing music of any kind adds a familiarity to audio aspect of the game. The decision may have just been: we need music for this new NES level and there's not space for new music-- ok, let's reuse this Jungle music. I'm getting more esoteric with my thoughts about how the audio draws the player more deeply into the game as I'm reading/learning more about the subject. I think with a game like Contra, hearing the explosions and firepower, etc, helps the eye to sort out the barrage of moving images-- many of which are important to process quickly in order to stay alive. This is a different genre of platform game than Mario and more similar to Mega Man in that you have weapons/guns and have to shoot enemies to stay alive. Speaking of Mega Man, are there audio similarities between the two games? More research is needed. Also, I think the end game being so diatonic and scalar after hearing so much chromatic music with the fight with Red Falcon gives the sense that everything is restored to normal and is ok, even sound-wise. No more crazy sounds!
Below is my listing of the NES keys and tracks. One thing I did with this game was to compare the original arcade soundtrack against the NES soundtrack. Of course, there are differences between the NES version and the arcade version simply because of technology. By this I mean generally better sounds based on the more advanced technological abilities of the arcades. What surprised me was that there are also differences in key and tempo between the arcade and NES versions as well. In general, the NES tracks are faster than the arcade versions. The arcade as an entire game also has a more clear base in A minor. I wonder why the keys of some of these pieces were changed for the NES? Perhaps again, technological limits, but it's interesting to realize that whereas key relationships were important in the original arcade, yet they were lost to some extent when the game was ported to the NES. I'd love to connect with someone who can help me understand why key relationships weren't preserved in this game.
-Title Screen: (5 sec) A minor
-Introduction: (16 sec) E minor-- this track isn't in the original arcade version, love the breakdown at the end of the music here just before you start gameplay
-Jungle/Hangar: (51 sec) C minor-- by far the longest track in the game, intro doesn't loop
-Area Clear: (4 sec) E-- open 5th makes me wonder if I hear this in major or minor?
-Base Theme: (45 sec) Bb minor-- love the kid's taunt in the second section of this theme (though in minor), also has an intro of melody over drums that doesn't repeat, my favorite theme in the game
-Boss Theme: (35 sec) F# minor-- follows the common trend of a boss fight being very chromatic
-Waterfall: (41 sec) A minor-- this theme reminds me of Mega Man-- has a long intro (9 sec) that doesn't repeat at the loop point
-Snowfield: (35 sec) D minor-- love the rising thirds progression at the beginning-- E-G-Bb-C- and the high obligato when we reach tonic, has a short bass section that doesn't repeat at the loop point
-Energy Zone: (23 sec) F minor-- I definitely hear the kid's taunt again here, but more demonic with the tritone first theme in compound meter (divides by threes not twos), or else it could be heard as swung.
-Red Falcon's Lair: (34 sec) C minor-- has the longest intro that doesn't repeat, a Jaws-like opening (11 sec) that doesn't repeat at the loop point
-Red Falcon Dead: (8 sec) A major
-End Game: (39 sec) C major-- very diatonic and stepwise, scalar
-Game Over: (5 sec)A (I hear minor here, but the last arpeggio does have a C# in it...)