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posted
I took some time to type out some logistics for users curious about "notelock" in beatmaps, and how to avoid it. I also included formulas for converting uncommon 1/3 notes and 1/6 notes into hypothetical 1/2 notes, for songs/maps that use those snap divisors for jumps or patterns that would commonly be done in standard 1/4 note or 1/2 note divisors.

What is "notelock"?
"Notelock" basically means a beatmap's OD is too low for the BPM, essentially when the hitwindow of one note overlaps the hitwindow of another.
When the player misses a note in a pattern in this scenario, the following notes with overlapping hitwindows will not be able to be hit as the hitwindow of the last (missed) note is still technically active, resulting in every following note to be missed. The player commonly ends up failing the map when this happens.

How do I avoid "notelock" in my beatmap?
It's simple: Use a high enough OD. Read the chart I made below, find the BPM of your map, and set the OD of the map to at least the minimum mentioned values.

Maps with a BPM of 230 or lower generally don't have to worry about notelock, as the OD is commonly set higher than the posted minimum.
This post only really applies to harder beatmaps. Easier difficulties with a high BPM generally use 1/1 or even 2/1 patterns anyway. Only refer to this chart if your difficulty uses 1/2 note patterns or higher.


Here are minimum OD values to prevent "notelock" at high BPM.
For maps that use (1/3, 1/4, etc.) notes as hypothetical 1/2 notes, first calculate the hypothetical 1/2 note BPM.
Formulas: (BPM*6)/2  for 1/6 note -> hypothetical 1/2 note 
(BPM*3)/2 for 1/3 note -> hypothetical 1/2 note
(BPM*2) for 1/4 note -> hypothetical 1/2 note
(BPM*3)/4 for 1/3 note -> hypothetical 1/4 note
(BPM*6)/4 for 1/6 note -> hypothetical 1/4 note

Example: 185BPM 1/3 note streams
185*3 = 555
555/4 = 138.75 hypothetical BPM

200BPM = 150ms per 1/2 note (OD 5 MINIMUM)
210BPM = 142.857ms per 1/2 note (OD 5.7 MINIMUM)
220BPM = 136.364ms per 1/2 note (OD 6.4 MINIMUM)
230BPM = 130.435ms per 1/2 note (OD 7 MINIMUM)
240BPM = 125ms per 1/2 note (OD 7.5 MINIMUM)
250BPM = 120ms per 1/2 note (OD 8 MINIMUM)
260BPM = 115.385ms per 1/2 note (OD 8.4 MINIMUM)
270BPM = 111.111ms per 1/2 note (OD 8.9 MINIMUM)
280BPM = 107.143ms per 1/2 note (OD 9.3 MINIMUM)
290BPM = 103.448ms per 1/2 note (OD 9.7 MINIMUM)
300BPM = 100ms per 1/2 note (OD 10 MINIMUM)

!301BPM IS MAXIMUM FOR OD 10!
!Above 301BPM using DT to achieve proper OD is recommended!

302BPM = 99.338ms per 1/2 note (OD 10.08 MINIMUM)
~
410BPM = 73.171ms per 1/2 note (OD 10.42 MINIMUM)
~
440BPM = 68.182ms per 1/2 note (OD 10.97 MINIMUM)
450BPM = 66.667ms per 1/2 note (OD 11.08 MINIMUM)

Formula for milliseconds per 1/2 note:
(BPM*2)/60 = n
1000/n = ms per 1/2 note

Next is a simple OD chart, taken from the Osu!wiki.

The full hitwindow in milliseconds decreases by 1ms per 0.1 OD, or 10ms per 1 OD.

The following values are for the hitwindow for a 50. DT scales these values by 2/3, while HT scales these values by 3/2.
The OD value itself is determined by the hitwindow for a 300.
OD -4.42 = 266ms    (OD 0  HT)
OD -3.75 = 259.3ms (OD 1 EZ+HT)
OD -3.08 = 252.7ms (OD 1 HT)
OD -2.42 = 247.3ms (OD 3 EZ+HT)
OD -1.75 = 239.3ms (OD 2 HT)
OD -1.08 = 232.7ms (OD 5 EZ+HT)
OD -0.64 = 228.7ms (OD 2 HR+HT)
OD -0.42 = 226ms (OD 3 HT)
OD 0 = 199.5ms
OD 1 = 189.5ms
OD 2 = 179.5ms
OD 3 = 169.5ms
OD 4 = 159.5ms
OD 5 = 149.5ms
OD 6 = 139.5ms
OD 7 = 129.5ms
OD 8 = 119.5ms
OD 9 = 109.5ms
OD 10 = 99.5ms
OD 10.08 = 77ms (OD 6 HR+DT)
OD 10.42 = 73ms (OD 9 DT)
OD 10.97 = 67.7ms (OD 7 HR+DT)
OD 11.08 = 66.3ms (OD 10 DT)


Hope this is helpful to beatmappers and players alike.
posted
This looks really interesting. I think I've experienced this "notelock" before when I play, but I never knew that made it occur. I thought it was the AR, but I guess I was wrong. This is really helpful C:
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