The process of producing music is basically the process of composition → arrangement → recording → track down. Once you have recorded the performance of each part on the MTR（An equipment called a multitrack recorder.), you have to work down the track. Ordinary, CD is 2 tracks of left and right stereo like cassette tape. For this reason, it is necessary to reduce the number of tracks and combine them into two tracks and dubbing to two-track media. This is called track down. You will not need a mixer for track down. There are various specialized books on how to track down, so let’s refer to them.