I have two versions of the same song; a vocal version and an instrumental. The vocal version is significantly louder than the instrumental.
I’m familiar with using Equalization and Bass and Treble to make tracks louder, but I only want to increase the volume of the instrumental to match that of the vocal version.
Is there any trick to do this, or do I just have to rely on trial and error?
If you only have a few songs to match, it’s often better to do it by ear… Run the Amplify effect on both tracks and accept the default (or run the Normalize effect). Then if the songs are not equally loud, reduce the louder one to match.
Or, try the [u]ReplayGain plug-in[/u]. (These applications, as well as ReplayGain and Apple Sound Check) are intended for volume-matching of your entire music library.
Or, you can try [u]MP3Gain[/u] or [u]WaveGain[/u], which are stand-alone applications.
Note that most commercial songs are normalized (“maximized”) so most of the time you have to make the louder track quieter to match the perceived volume. For that reason, the volume-matching applications tend to make most of your songs quieter.
I’m familiar with using Equalization and Bass and Treble to make tracks louder
That’s really not the purpose of those effects. In fact, if you boost the bass or treble (or if you boost anything) you often have to reduce the overall volume to prevent clipping (distortion).