Add background music to mp3 audio files (Adobe Audition cs6 as an example):

1: Run Adobe Audition cs6 and switch to multi-track.

2: Right-click the blank space of audio track 1--Insert--File, and insert the required background music.

3: Right-click the blank space of audio track 2--Insert--File to insert the mp3 audio file.

4: Use the move tool to drag the waveform of track 2 so that its relative position to track 1 meets the requirements.

5: Press the play button to listen. When you are satisfied, click: Multi-track mixing--mixing to a new file--complete mixing. When the mixing is completed, people will automatically jump to the waveform editing window. , click: File--Save As, in the pop-up Save As dialog box, name the file, select the storage format, specify the storage location, and save the file.

The above is purely done by hand. If you are satisfied with my answer, please accept it in time.