As you adjust your iPhone’s volume with the physical volume buttons on the left edge of the handset, each button press equates to a tiny amount of adjustment to the volume level itself. If you’re trying to make drastic changes to the handset’s volume all in one fell swoop, then this means pressing the volume button(s) several times in rapid succession until you get it right where you want it.
A newly released and free jailbreak tweak dubbed VolumeStep13 by iOS developer Randy240 attempts to make this process a little bit easier by allowing jailbreakers to set a custom volume step amount. In a nutshell, this means each button press can have more or less influence over the volume level than it would on a stock handset, and as you might come to expect, the step amount is fully configurable.
