In the NES version of Tetris, how much faster is a soft drop?

In terms of frames, how much faster is a soft drop in Tetris for the NES?

Like, on level 0, the piece moves down one cell every 48 frames. When you soft drop the piece, is there a specific equation for how fast it falls?

Like, if x = the normal frames between cell drop and y = the frames between each cell drop during a soft drop, is there an equation for y in terms of x?

Solution 1:

Soft drop speed is twice as fast as normal gravity (or =1/2G). So on level 0, where normal gravity is one cell per 48 frames, soft drop is one cell per 24 frames.

Source

Solution 2:

On NES Tetris, the gravity of soft drop is 1/2G, which means it drops 1 block every 2 frames, equal to the gravity on Level 19. This applies until Level 29, where the gravity goes faster than soft drop. In that situation, soft drop doesn't do anything other than add a bit of score.