Many times, you’ll be pleased with your recordings, but there’s just something — a buzz, some fizz, a whistle, a harmonic — that doesn’t sit quite right. In these cases, parametric EQ, which offers you the ability to adjust the EQ frequency, the gain, and the bandwidth (sometimes labeled “Q”), is just the tool.
To start, narrow the Q so that your EQ curve looks less like a bell and more like a spike. Then increase the EQ gain substantially (you may need to turn down your monitors!). As you play back your track, slowly sweep the frequency from the bottom to the top. When you get to the errant frequency, you’ll know it because your track may suddenly become distorted or overloaded, and the whistle or harmonic will overwhelm everything else.
Once you’ve found your frequency, you can then cut the EQ gain for that frequency and adjust the bandwidth to taste. It takes some practice, but you’ll find that using this technique you can very effectively dial out most narrow band irritants.