Double-click your preferred digital audio workstation.
Open a new session. The exact command process for this varies according to which program you use, but the command is typically located in the file menu. For example, if using Logic, click "File" and "Open New."
Click "Import Audio." Select the song from which you want to remove the melody line.
Open the equalizer interface. This is typically located under the tools or effects menu. An equalizer lets you mute certain frequencies in a sound file. Since you can't simply mute the individual melody line track, as you can with multitrack files, you need to zero in on the exact frequency.
Click "Play" to roll the track.
Click on the equalizer curve and drag it around the spectrum analyzer grid. The vertical axis represents volume, and the horizontal axis represents frequency. As you drag the curve into different shapes, different frequencies become louder according to where on the grid your cursor is. When the melody is at its loudest, stop moving the curve. The specific frequency remains highlighted.
Drag the "Gain" slider dial to zero. Gain is the audio term for output level. The "Gain" slider dial applies to whichever frequency is highlighted. By sliding it to zero, you reduce the output level of the highlighted frequency. This process may not remove all of the melody in one go, because audio can contain a range of frequencies. Repeat the process until the melody is gone.
Click "Save."
Open your preferred digital audio workstation.
Select the multi-track mix from the file menu. The precise command process varies, but you typically click "File," "Open Recent" or "Recent Session" and select from the drop-down menu. This opens the work in progress as a multi-track session. Each audio channel can be individually edited, deleted or modified.
Identify the melody track. Click "S" on each audio channel to solo it. Soloing mutes everything else.
Click "M" on the audio channel when you identify the melody line audio. This mutes it, leaving only the backing track.
Click "Save" and quit.