Different from each other

Question

The answer to this puzzle consists of two words with 14 letters in total.

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Hint1

Each rectangle corresponds to exactly 1 or 4 characters (although predominantly letters)

Hint2

The only one corresponding to a non-letter is "53TLA". The rest are letters.

Answer 1

I think the 2 words are:

CHROMATIC SCALE

This is 14 letters.

Initial observations:

Small Box 1 looks like 'alpha prime' or something

Small Box 2 looks like A P I S in sequential order of number of sides. This seems to clue "BEE" (synonym of apis)

Small Box 3 looks like the element CARBON, or C for short

Small Box 4 looks like "500" or "D" in Roman numerals

Small Box 5 looks like XVI15

Small Box 6 looks like XVI16

Small Box 7 looks like 9.82 distance over time, which clues GRAVITY or G

We notice a pattern:

A(lpha), B(ee), C, D, ? ? G. This looks suspiciously sequential.
The title alludes to differences, and we notice that if we look at the two triangle images, they are identical except for "5" and "6". Using those as indices into the alphabet, perhaps they indeed represent E and F. UPDATED with OP's help: However, there is a different, correct mechanism. If we take the baseline to mean 'base' and XVI as 16, we get a rebus depicting "(15) in base 16" and "(16) in base 16" respectively. This clues either "F" and "10" if we take it literally as conversion from decimal, or "E" and "F" if we interpret it as the nth digit in base 16, counting from zero. The latter interpretation is correct as it falls into the overall pattern as expected.

Next, looking at the larger rectangles, they all follow a pattern:

PRIOR LETTER, 53TLA / NEXT LETTER, B

So what is 53TLA? Thought it was an airport code but that led to a dead end. Hint 1 said the chars were "predominantly letters" which meant that it was presumably the only non-letter. Hint 2 repeated this information.

The only other meaning we can find to "TLA" is possibly "ALT" backwards, clueing 'ALTERNATE'. Perhaps indicating this is not a letter, which we already knew. Checking ASCII codes, the 53 might indicate "5", or "#" if backwards like ALT was. UPDATED with OP's help: ALT-35 keys a # sign (or other character value as appropriate), at least on Windows computers if you use the numpad. Possibly other computers. This is not something I was aware of. So that is the meaning of "ALT".

After much thought... the breakthrough.

If we take 53ALT as "#", what actually is A#/BB, C#/DB, D#/EB?
Noticing we are limited to letters A-G, these look like musical notes. In fact, if we take the second 'B' as lowercase, we get a Flat Sign... "A#/Bb", etc. These of course indicate the chromatic notes between the primary musical notes above and below. It is now seen that ALT may have been a clue that A# and Bb, etc. are alternates of each other.

In conclusion, the image as a whole represents a

CHROMATIC SCALE (found in music, each step different from the others):

A
A#/Bb
B
C
C#/Db
D
D#/Eb
E
F
F#/Gb
G
G#/Ab