There is lot of audio editor apps are available in the play store but power director tool is best one.This app is powerful video editor ,but we use also a audio editor as well.

How To Edit
Choose which track’s you want from library,you can add multiple tracks in the time line,easily split and delete unwanted portion from audio layer.Here Below the tutorial video is there .this video about how to add vocal and chorus part in Karokee tracks.

After completing the full editing portion you can export the video.(note : this app export video file only).but we want audio layer right so simple use video to audio converter app done the process.