Analysis: The evolution of Final Fantasy battle music

Youtube is really a great resource for video game music.  I regularly listen to game soundtracks that I can't find elsewhere on it.  Often, they're organized into playlists-- so if you're wanting to hear a bit of game music, YouTube is a good bet.  I stumbled upon a video that easily allowed me to do a great musicological comparison of game music.

I've been wanting to do a vertical tasting sort of comparison: same composer, same series, same game function.  In this case, that corresponds with Nobuo Uematsu, Final Fantasy, and battle music.   Based on this incredible video, comparing these themes was easily possible.  I noted some basic musical features of these battle tracks: speed, key, length, and form.

I had three hypotheses:

1- that the music would get longer over time as technology improved

2- that the music would change most significantly between game systems

3- the the music would share similar compositional traits not only because it's composed by the same composer, but also because "Battle music" shares a common function in these games.  

The table below shows each theme's composer, length (time), tempo (Beats per minute) key, and notable features.

Game	Composer	System	Length	BPM	Key	Notable features
FF 1	Uematsu	NES	45 sec	150	G minor	The beginning of awesomeness
FF 2	Uematsu	NES	42 sec	150	A minor	Also a simple form similar to the original
FF Legend	Uematsu	Gameboy	36 sec	162	C minor	Repetitive phrases that vary pitch stepwise
FF 3	Uematsu	NES	43 sec	159	A minor	Prominent percussion
FF Legend 2	Uematsu	Gameboy	41 sec	171	F# minor	Awkward connection at loop point
FF 4	Uematsu	SNES	49 sec	167	A minor	Teeters between F major and A minor
FF 5	Uematsu	(SNES)	34 sec	162	A minor	Very simple in form
FF 6	Uematsu	SNES	56 sec	169	A minor	A8-B8-A8-C10 form
FF 7	Uematsu	Playstation	1:10	177	F minor	First game where instruments (midi, brass) sustain over the return loop
FF 8	Uematsu	Playstation	1:27	165	A minor	First use of irregular meter in battle music
FF 9	Uematsu	Playstation	1:12	160	A minor	Also uses irregular meter
FF 10	Uematsu	Playstation 2	1:40	190	C# minor	Irregular meter again
FF 10-2	Eguchi	Playstation 2	44 sec	179	A minor	Very short battle theme for its time
FF 11	Mizuta	Playstation 2	1:45	165	B minor	Two big sections, very strong A-B feel
FF 13	Hamauzu	Playstation 3	1:15	163	F# minor	Prominent use of looping and multi-tracks
FF 13-2	Mizuta	Playstation 3	2:29	143	C minor	The longest battle theme to date
FF 14	Uematsu	Windows PC	1:47	125	C minor	Teeters between major and minor like FF4

One note, the above video doesn't allow the entirety of the FF6 battle theme to play-- instead hear all of it here.  Also, as is obvious, though Final Fantasy Legend I and II were for the Gameboy and arguably for a different series, I included them here to study variations in Gameboy audio and to flesh out my understanding of Uematsu's compositional style.

How did my hypotheses do?

1- The battle music length does increase generally over time.  FF 6, 7, and 8 are each a notable jump in length over their predecessors.  The longest battle music is for 13-2, which is as long as three repetitions of the original music.

2-The music makes a jump in length with each new platform.  The NES and Gameboy share similar track lengths, but the SNES, Playstation, and Playstation 2 make large gains.  To date, 13-2 for the Playstation 3 has the longest battle theme track.

3- The battle theme tempos follow an overall arch through time.  From 150 beats per minute in FF 1 accelerating to 177 BPM at FF7 and peak at 190 BPM in FF 10 before relaxing to 125 BPM in FF 14. Of course, the battle themes are one of the most energized portions of gameplay, so one would expect them to have a rapid pulse.  I'm wondering more about the acceleration and then slow down we've seen of the battle music over time.  Could technological limitations have impacted this somehow?  Pacing of other music in the games?  Deliberate decisions to match with onscreen visuals?

What I hadn't predicted:

Each battle theme is in minor mode!  Although 4 and 14 seem to verge on major I hear each squarely in the minor.  A minor is the overwhelming key of choice for Final Fantasy battle music.  The 16 themes I list use 8 keys.  Repetitions:
A minor (8) FF 2, FF 3, FF 4, FF 5, FF 6, FF 8, FF 9, and FF 10-2
C minor (3) Final Fantasy Legend, FF 13, and FF 14
F# minor (2) Final Fantasy Legend 2 and FF 13

Considering composers, Eguchi and Hamauzu give significantly shorter battle themes than the contemporary battle themes.  Eguchi continues the classic tonality of A minor while Hamauzu uses the more rare F# minor.

What do you notice when you compare these battle themes?  What other composers and tracks should I considered as they develop over time?  How is this sort of observation enlightening?