I learned that in computer there is a limit of amplitude that you can store of a sample. (0 dB) If you boost the sound past that point then clipping occurs.
In my game I have 1 BGM (no clipping, average loudness -0.3dB) and 1 SFX (no clipping, average loudness -0.3dB) now why when I play these two file at the same time, it sounds like clipping occurs? It's like two waveform adds up each other and resulting in over 0 dB. But this is a playback, not storing in a limited space so clipping should not happen at all?
Another question, is it impossible to create a clipping-free game? Because unlike conventional music which you carefully mix things to a perfect shape, in a game you never know that your player will or won't do something outrageous and make a really loud sound like gather 100 enemies and destroy them at the same time.