Open Sound Forge. Double-click the desktop icon, it may take a few seconds for Sound Forge to launch fully. When it does, a default blank page opens. One advantage of Sound Forge is that you can customize the layout to suit whichever application you are currently performing, in this case mixing.
Click "View" and select "Spectrum Analysis." This opens a visual spectrum analyzer interface in the Sound Forge interface. Click "View" and select "Plug-in-Manager." The former allows you to tweak the frequencies present in the audio; the latter allows you to add plug-in effects like compression, distortion, reverb and delay.
Right-click on the blank space in the Sound Forge interface and select "New." A dialog box appears, from which you can browse for audio files. Find your guitar audio file and click on it to load it into the Sound Forge interface. Click "2" in the "Channels" sub-menu so the audio opens as a stereo channel.
Click on and highlight the part of the guitar track that you want to sound like death metal. If it is the whole track, then highlight the entire audio file.
Click "Effects" and select "Distortion." Death metal guitar is characterized by an intense, deep and heavy tone typically created by a combination of distortion and other effects. On the distortion interface there is a "Level" parameter. Set this quite high to increase the intensity of the effect. Tweak the other parameter controls, including "Drive" and "Tone" to enhance the timbre of your guitar.
Press "Play" to listen back to the audio. You'll notice that the guitar has a heavier tone than before. If it is too heavy, reduce the "Level" parameter.
Click "Effects" and select "Compression." This effect tempers the dynamics of an audio track by cutting the volume peaks and boosting the volume dips to create a tighter-sounding piece of music. The other benefit of compression is that it allows you to mix the audio louder once the peaks and dips have been smoothed out. By "abusing" the compression settings, you can create a distinctive "fuzzy" sound, similar to the sound that Slayer uses. Set the "Threshold" parameter to around 80 percent to achieve this.