Adjust Volume (No noise) is a handy and simple app that controls your volume and works with most apps. This is ideal if your volume buttons are broken and need an alternative.
Changing the volume is easy: swipe up or to the right to raise it; swipe down or to the left to lower it. Double-tapping will automatically mute and holding your finger will gradually raise it. You can also pin your volume setting to the home screen.
Most music and game apps run smoothly and it's incredibly easy to use.