Open your preferred audio production software, for example Apple's Logic, Pro Tools or Adobe Audition. Double-click the icon on your desktop to open the program. If you don't have a desktop shortcut, click "Start," select "Programs" and click on the name of the program. If using a Mac, open the "Applications" folder and select the program from there.
Click "Import" from the "File" menu and select the vocal track that you want to master. This opens the vocal audio file in the mastering program. Typically the audio file will be represented by a graph. The graph will feature peaks and dips that represent high and low signal levels.
Open "Multi Band Compressor" from the "Tools" menu. A multi band compressor splits the audio file into four bands. This tool enables you to boost individual frequency ranges, from sub-bass to very high.
Adjust the slider dial assigned to the lowest frequency band. Move it up to boost the frequency and down to cut the frequency. Do this for each frequency band. Click "Bypass" to hear the audio without the mastering effect to compare the two.
Open up the "Bus Compressor" tool from the "Tools" menu. The bus compressor "squashes" the overall frequency band of the audio to boost the quiet sounds and make the louder sounds softer.
Adjust the "Threshold" setting by moving the virtual slider dial with your cursor. The threshold parameter governs the level at which the compressor begins to act. Set it very low to boost only very quiet signals, such as breaths, and cut very loud signals, such as full-on power vocals. Set it high to boost all signals on either side of the average level.
Adjust the "Ratio" slider dial to govern how much compression is added. Set it low to gently reduce or enhance the signal; set it high to increase the intensity of the effect.
Select the "Scissors" tool from the menu. Zoom in on the audio graphic and scroll left. The first peak on the graph after the initial flat line represents the first sound on the audio. Click the scissors just to the left of the first peak to cut off any residual microphone noise present at the start of the track. Scroll right and snip just to the right of the final peak on the graph. This is called "topping and tailing."