Hitsounds from hitcircles and sliders must be audible. These provide feedback for the player, and having them silent in a rhythm game doesn't make much sense. If you don't like the default sounds, then find replacements rather than silencing notes. You can use hitsounds from the Custom Hitsound Library or easily find others online. Lowering the volume of a few notes to provide a dampened effect is usually fine, but complete silence is always unacceptable. The end of a spinner (or even the entire spinner) the sliding sound of a slider, and the end of a slider can be silent, but only do it if it makes sense. Finally, you cannot silence both slider ticks and slider slides together.The rationale behind this rule is that it provides, using audio cues only, information to the player as to whether or not they hit a pattern successfully. Since this is a rhythm game, a significant amount of the player's brain power goes towards interpreting audio cues, so representing their success at a pattern using visual cues only doesn't make much sense.
If the audio behaves in the same way whether the player hit an object successfully or not, something is wrong.
In the case of sliders, slide sounds on their own, and tick sounds on their own, are each capable of conveying the necessary information to the player. If both are missing, the problem I described appears.
Discuss.
