Do the audio files playback normally in other players? What sound card are you using? Did any FX plug-ins inadvertently get added to the SF chainer.. EQs, compressors and such? They FX chainer could be hidden. (Veiw> Plug-in Chain). If it is just a low volume issue, Check the 'volume fader' in "View> Hardware meter". Otherwise SF does not change the tonality w/o some kind a processor. It could have something to do with your soundcard or converter. Check which audio device SF is using.. "Options> Preferences> Audio".