What does this arpeggio sound effect from NES Dr. Mario mean?

Solution 1:

The sound effect occurs when the 10th (20th, 30th, and so on) vitamin capsule appears in Dr. Mario's throwing hand. Each time the sound effect occurs, the drop speed of the vitamin capsules increases slightly.

Details

The sound effect occurs up to a maximum of 49 times on a level, meaning there are 50 possible drop speeds for each SPEED setting.

On the NTSC game, each level starts with a drop speed of

• 1.5 rows per second (40 frames per row) when the SPEED setting is LOW
• 3 rows per second (20 frames per row) for MED
• 4.3 rows per second (14 frames per row) for HI

Each time the sound effect occurs, the drop speed changes to the next speed in this list:

rows per second: 1.5 1.6 1.7 1.8 1.9 2 2.1 2.3 2.5 2.7 3 3.2 3.3 3.5 3.8 4 4.3 4.6 5 5.5 6 6 6.7 6.7 7.5 7.5 8.6 8.6 10 10 10 10 10 10 10 10 10 10 10 10 12 12 12 12 12 15 15 15 15 15 20 20 20 20 20 30 30 30 30 30 30 30 30 30 30 60

(frames per row: 40 38 36 34 32 30 28 26 24 22 20 19 18 17 16 15 14 13 12 11 10 10 9 9 8 8 7 7 6 6 6 6 6 6 6 6 6 6 6 6 5 5 5 5 5 4 4 4 4 4 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 1)

On the PAL game,

• LOW starts at 1.6 rows per second (32 frames per row)
• MED starts at 3.1 rows per second (16 frames per row)
• HI starts at 5 rows per second (10 frames per row)

The list is:

rows per second: 1.6 1.7 1.7 1.9 2 2.1 2.3 2.5 2.6 2.9 3.1 3.3 3.6 3.8 4.2 4.5 5 5 5.6 6.3 7.1 7.1 8.3 8.3 8.3 10 10 10 10 12.5 12.5 12.5 12.5 12.5 12.5 16.7 16.7 16.7 16.7 16.7 16.7 16.7 16.7 16.7 16.7 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 50

(frames per row: 32 30 29 27 25 24 22 20 19 17 16 15 14 13 12 11 10 10 9 8 7 7 6 6 6 5 5 5 5 4 4 4 4 4 4 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1)

Sources

• The Dr. Mario manual mentions on page 10 (PDF page 11) "The speed that the vitamin capsules drop increases slightly after every 10 capsules."

• The Tetris.wiki article for Dr. Mario describes the behavior for the NTSC game in the Gravity section. (Note: the 2019-09-08 revision was used when writing this answer.)

• I investigated further on my own.