The key to understanding this puzzle is understanding the ... well ... key.



There are two main problems with this key:

• The only numerical clue is written in British notation.
  
• We don't know how to read music.

Like us, those in the U.S. are going to read 0,5 as two separate numbers. But in reality it's just a single number. In the UK they use comma (,) as the decimal separator. Which means what the key is trying to tell you is that the notes in bottom row are worth 0.5 each.


Now, for those who don't know how to read music, the little note with the tail:



actually means connected notes like these:



So, basically, connected notes are worth 0.5 per dot. And since there are only ever two dots in any connected note, connected notes are always just worth 1 point.

Understanding the next part, unfortunately, will probably end up requiring you to ask the game for a hint. The hint will tell you that each row in the pyramid is worth double the row below it.

Therefore:

• Notes in the bottom row (connected notes) are worth 0.5 points per dot.
  
• Notes in the next row, solid stand-alone notes are worth 1 point per dot.
  
• Notes in the 3rd row, hollow stand-alone notes are worth 2 points per dot.
  
• Hollow empty circles are worth 4 points each.
  
• Oh, and finally, even though the hollow empty circles are on two different lines, since they're the same color, they contribute to a single number.

Now that you know the value of each kind, just count the dots and apply the multiplier for each dot kind. Each color change represents a new digit in the code.

The final number is 39866.