Cubase Mixdown and post soundclound changing quality

Hi all,
I am using Cubase 5 and MS Windows 8.
Finish record my song, play back with computer OK, sound great. I upload to SoundClound and listen from
Cell phone the back ground music OK but the recording (Saxophone) is terrible. My Saxophone sound like far away.
Please give me some advise.
Thank you
DoVo