Is there any way in Xcode to improve the audio playback quality?

I'm making a app that gives users a rich collection of natural sounds. However the tracks are in 48khz and I need to reduce them to 38khz so that the size of the app could go down.I'll be using AVFoundation to play the audio. Now I'm worrying that this will lead to reduction in sound quality. Is there any way in Xcode to improve audio quality during playback.