Double-click the Acid Pro 4 icon on your desktop to open the program. If you don't have a desktop shortcut, click "Start," and select Acid Pro 4 from the "Programs" menu, if using a PC. For Mac, single-click the "Applications" folder at the bottom of your screen, and select Acid Pro 4.
Click "File." Select "Open," and click on the track you want to mix from the files menu. If the track in which the vocals you want to mix was the last one you saved, it opens automatically.
Close the file browser on the bottom left of your screen to expand the "Mixing Console" window. The default window configuration for the program is arranged so that the channel strips take up the top half of the screen and the bottom half of the screen is split vertically between the mixer section and the file window.
Double-click on the first vocal track in "Channel strip" window to highlight the vocal in the "Mixing console" window.
Play the track. Adjust the level of the vocals by moving the virtual slider dial in the mixer up or down. Aim for a level in which the vocals clearly are audible but not overpowering. If the red LED warning light on the channel strip flashes, the level is to high.
Click "Tools," select "Plug-In Effects" and select "Compression," which limits the dynamic range of a piece of audio. It cuts the high volume signals and boosts the low-level signals so that entire audio sits within a smaller dynamic range. This adds clarity and punch to the vocal. Adjust the "Threshold" parameter to determine the level at which the compressor begins to act. Set it high if you want moderately loud and moderately quiet signals to be brought within range. Set it low if you only want very quiet and very loud to be affected.
Select "Equalizer" from the "Plug-In Effects" menu. Equalization is similar to compression, but it boosts frequencies. The equalizer interface has a series of virtual dials that represent a frequency range. Turn the dials with your cursor to boost or cut various frequency ranges. For example, cut the frequencies below 80Hz to eliminate the "popping" sound that occurs when a singer makes a "P" or "B" sound.