我就是这样做的，不用很复杂。
1.start CE
2. view --> multitrack view
3. use windows exploer to find your background music, say changjiang.mp3, mouse drag to CE track 1
4. In multitrack view, mouse right click and hold it, move the whole block to the leftend
5. in tract 2, click the red "R" button
6.click the lower left red buttton, now, recording starts.
That is it.
7. After record finishes, you can adjust the sound volume and echo. Double click to get into "edit waveform view"
8. to add echo, go to effects-- delay effects-- echo and select one of them.
9 to adjust sound volume, effects -amplify -- select whatever you want
10. go back to multitract view(view multitract view)
11. edit-- mixdown to file -- all waves
12 save to mp3

That is it.