Every sg4 comes with a music player with sound options if you're having trouble hearing a song it probably the quality of the music file was set to low for space compression try getting another copy,or go to music>soft key(menu)>settings>check the box labeled-smart volume and feel free to check the rest of the options in this menu.
Also being a former SG4 user of course U.S. not Vietnamese but did you try installing musicfx.apk give some good options to improve sound quality.
If this doesn't help to boost your sound to better quality, then obviously the question is misinterpreted and to help us help you,it might be beneficial for all of us if you can find a different way to phrase the question, thank you and good luck!