I'm using background music and sound effects in my android-game. The Problem is that these sound effects differ in their loudness very much. And some of them are much to quiet. Unfortunately, the quite ones can't be amplified without overdrive. How can I increase their loudness?
Have the sound effect files been normalised? If not, I'd start by normalising them as this operation will analyse the file, find the highest level and will then increase the level of all samples so that the highest value sits at 0dB. If you are not familiar with audio software I'd suggest downloading something like Audacity and then look at the manual for normalisation.
You'll need to modify the gain structure by compression/limiting or manual volume automation.
You could use a brickwall limiter, but make sure by listening and comparing that it actually results to increased volume and not decreased volume as crushing dynamics can result in either one depending on how the limiting is done or how the sound reacts to it.
You could try some EQ or harmonic exciters as well. Or a "volume maximizer" in the style or Waves MaxxVolume or RVox.
Cutting some bass out can free some headroom for you to increase more volume. Since the bass in sfx is not that great and can make player's ear tired. I once do a rapid laser gun sound with bass uncut and man! that's very annoying.
When you dry up the sfx it may not sound that great when listened alone but when you play the game with your awesome soundtrack then it started to sound great! (Especially song with kick drum sound)
Try cutting unnecessary low end and boosting around 1-3k.