Visual sync is a new feature of ArrowVortex intended to assist in syncing charts with complex timing or live-recorded songs with floating BPM.
To do so, three actions have been implemented:
Insert bounding BPM change: Ctrl-B
Destructive shift: Alt-B
Non-destructive shift: B
The feature is only available in time-based view, aka cmod view.
The way the feature operates is by adjusting nearby BPM values such that an anchor row will line up with where your mouse cursor is pointing at in the waveform.
Two modes are available: cursor anchor and receptor anchor, which can be changed via Tempo -> visual sync anchor menu.
In receptor anchor mode, the row shifted to mouse cursor is the row your receptors are at.
In cursor anchor mode, the row shifted depends on currently selected snap. The row shifted will be the closest row of this snap near the mouse cursor. For instance, if your current snap is 8ths, then the closest 8th row at the mouse cursor position will be shifted.
The two types of shift determine which BPM changes are affected.
Destructive shift will choose to adjust previous BPM change which may be arbitrarily far away and will NOT compensate for any future BPM changes, thus potentially ruining sync of the whole chart hence the name, destructive.
In order to constrain it, a convenience action is added -- insertion of a bounding BPM change which will just insert a redundant BPM change at the anchor row.
Using these two actions, you can adjust sync in charts with relatively sparse timing changes, by adding bounding BPM changes at locations where the song changes tempo and then destructively shifting some notes into place to fine-tune that BPM to its true value.
This will only modify BPMs within the beat of the anchor, only changing the timings within that beat with the exception of 4ths which will also add in previous beat.
It will create additional BPM changes at the start and end of the beat if no other ones are present. This can be used to shift off-sync notes into their correct spots in an otherwise mostly synced chart or it can be used to deal with syncopation or for color theory purposes.