Open your preferred audio production software, for example Pro Tools, Mixcraft or Reason. This opens the most recent project you worked on. If this isn't the correct song, click "File" and select "Open Recent." Select the correct project from the drop-down menu.
Click "S" on the channel strip to solo the sound you wish to fade out. This mutes the other channels so you can hear the audio in isolation.
Click "Tools" and select "Automation." This represents the audio as a wave form graphic, inside a grid. The vertical axis represents volume and the horizontal axis represents time, measured in beats. There is a base line near the bottom of the rectangle that represents zero volume.
Click the cursor on the point where you want the sound to start to fade. Click it again at the point where you want the sound to completely disappear into silence. This creates an automation line, which represents the intensity of the volume fade. The steeper the line, the quicker the fade-out.
Adjust the line by "dragging" it downward. Each click establishes a new automation point; the volume reduces in proportion to the angle of the line between two automation points. Once you've created a satisfactory automation line, click away from the sound wave graphic to close it.
Open your preferred audio production software and open the song to be faded. Click "File" and select "Export as Wav." This renders the entire mix as a single, lossless audio file. When prompted, name the file "Song Title Final Mix," replacing the words "Song Title" with the actual name of the song.
Click "File" and select "Open New." This opens a blank session. Click "File" and click "Import Audio." Select the file you saved in step 1. It will load into an audio channel.
Click on the file to highlight it. Click "Automation" from the "Tools" menu.
Play the track and stop it at the point where you want the fade-out to begin. Click the cursor on the start point of the fade.
Click the cursor on the zero line at the point where you want the song to go completely silent. This creates a sloping line. Click beneath the line to adjust the shape of the slope, to create a more gentle fade.