Hello! The osu! standard Ranking Criteria currently states that rhythm-related rules and guidelines are based around songs of 180BPM with 4/4 time signatures. We've received feedback about how this is confusing to adapt in certain situations -- specifically due to a proposed batch of Normal difficulty guidelines -- so we've developed a short reference for how BPM scales with Ranking Criteria content.
We'll be using the following proposed Normal difficulty guideline as an example: Include a 1/1 or longer gap in rhythm for every two measures of gameplay.
For the sake of simplicity, think of 180BPM as a midpoint.
- As a song’s tempo goes from 180BPM to ~120BPM, guidelines become more lenient. For this example, increased frequency of 1/2 rhythm is generally okay to the point of almost constant 1/2 chains at 120BPM.
- As a song’s tempo falls below ~120BPM, 1/4 rhythms can be slowly introduced. Closer to 120BPM, that would mean very rare 1/4 rhythms in chains of 2 objects or so.
- As BPM lowers further, more 1/4 rhythms are acceptable until reaching 90BPM, where double the density of existing guidelines apply.
This low BPM range could easily be equated to increasing tempo from the 180BPM base.
- As a song’s tempo rises from 180BPM to ~240BPM, less 1/2 rhythm is acceptable.
- Near 240BPM, minimal 1/2 rhythm should be used.
- Beyond 240BPM, no 1/2 rhythm should be used, just as maps above 120BPM should avoid ¼ rhythm.
For the most part, 120BPM and 240BPM act as breaking points for when a map’s rhythm should be doubled and halved according to guidelines. As BPM approaches these values, rhythm should reflect that through increases/decreases in density. For the sake of this example guideline, it's best to assume that using 1/4 above 120BPM or 1/2 above 240BPM is not a good choice for a Normal difficulty used as the lowest difficulty of a mapset.
The same general concept applies to other rhythm-related guidelines as well. As BPM goes from 180 to 240, active 1/2 should be gradually removed and frequency of conseuctive 1/2 sliders should go down. As BPM goes from 180 to 120, active 1/2 can gradually increase as well as 1/2 slider usage. (relates to Avoid more than three actively clicked 1/2 rhythms in a row and Avoid more than four consecutive 1/2 sliders guidelines.)
While this guide is oriented around guidelines for lowest difficulty Normals, it also applies to other content. For example, Easy difficulties require 4 beats of recovery time after spinners according to the Ranking Criteria. At 180BPM, that is true, however at 120BPM, it would be fine to use 3 beats of recovery, and that could gradually shift to 2 beats at 90BPM.
It's impractical to cover every rule and guideline in this reference sheet, but it should at least provide a clearer way to handle scaling BPM according to the Ranking Criteria. Thanks for reading!