This is a post from one of the Harmonix developers in the now defunct Dance Central forum. I decided to keep it for posterity.
For each move you perform “Almost” or better you earn “star points”. Flawless gets 100, Nice 60, Almost 15. Then we add up the total number of “star points” and divide them by the total potential number of star points (100 * [The Number of Moves in the Song] ). This gives us a number between 0 & 1 that represents the percent of star points you earned. We compare that number to the chart below, and award stars accordingly.
The scoring is a bit more complex. For each move you perform, the detection system returns a percentage of how well you performed the move. The absolute best you can do on a move is 100%, but each move has its own almost/nice/flawless thresholds. For example, a move could have 40% for the Almost threshold, 75% for Nice, 90% for Flawless. Based on the rating determined by the threshold, we award you “Score Points”, which are the same across difficulties.
After we calculate these “Score Points”, we calculate an additional bonus, based on the percentage difference between the rating you got, and the next rating above it (or 100% for Flawless). So if you did the move from the example above and we rated you at 89%, a nice, we’d give you a percentage of bonus points based on the distance from the present rating to the next rating. In this case, it’d be (89 [your rating] – 75 [the nice threshold]) / (90 [the flawless threshold] – 75 [the nice threshold]). That equals .93 or 93%, so you’d get 93% of the “nice” bonus at your difficulty level, which is you “Score Bonus”. Potential “Score Bonus” for a given move varies greatly between difficulties. Easy doesn’t earn much of a bonus, whereas Hard earns a huge bonus.
In DC2, there are only 2 multiplier states: 1x (normal) & 2x (peak). (At peak, the venue goes into the crazy awesome glowy look.) To get into 2x state, you can perform any sequential combination of “Nice” & “Flawless” ratings that add up to 4, where “Flawless” is worth 2 and “Nice” is worth 1. That means any you can get into peak state by performing:
Your Move Score (“Score Points” + “Score Bonus”), is multiplied by 4x if you are in peak.
Gold flashcards multiply your Move Score (“Score Points” + “Score Bonus”) by 4. This stacks with the multiplier explained above. Gold Flashcards are placed somewhat randomly, so you won’t always have the same number every playthrough of a song.
Your score is equal to the “Score Points”, plus the “Score Bonus”, multiplied by your multiplier, and the gold flashcard multiplier (when applicable). Your star rating is based on your move performance.
We want players to be competitive with each other on the leaderboards, be able to see small improvements reflected in their score. By adding huge bonuses based on your particular performance of a given move, we gain a number of benefits:
We want stars to be divorced from all the rest of scoring, so regardless of multiplier, gold flashcards, etc. you’ll reliably receive the same star rating as long as you get the same number of “Flawless” & “Nice” ratings.
Sadly, I didn’t write down who was it… so if you’re reading this, please reach out! I’d love to buy you a beer!