One of the most common questions I see asked in audio forums is if it’s better to equalize before compressing or vice versa. In many cases you’ll have one EQ before compressing and a second EQ after. Let’s take a closer look.
If a track has excessive bass content that needs to be filtered, you should do that before the compressor. Otherwise rumbles and footsteps, or just excessive low-frequency energy, will trigger the compressor to lower the volume unnecessarily. If you compress an unfiltered track, the compressor lowers and raises the volume as it attempts to keep the levels even, but those volume changes are not appropriate and will likely detract from the sound. The same applies for other frequencies that you know will be removed with EQ, such as excess sibilance on a vocal track or a drum resonance you plan to notch out. Therefore, you should do any such corrective EQ before compressing.
However, if you boost desirable frequencies before compressing, the compression tends to counter that boost. As you apply more and more EQ boost, the compressor keeps lowering the volume, reducing that boost. In fact, this is how many de-essers work: They sense the amount of high-frequency content in the sibilance range, then reduce either the overall volume or just the high frequencies, depending on the particular de-esser’s design. So when you’re using EQ to change the basic tone of a track, that’s best done after compressing. Again, there are few rules with art, and I encourage you to experiment. My intent is merely to explain the logic and theory behind mixing decisions that have a basis in science or that are sensible most of the time.
Figure 7.4 shows the Track Controls for a bass track from one of my projects, with three plug-ins inserted: an EQ, a compressor, then another EQ. The first EQ in the chain applies a gentle 6 dB per octave roll-off below 60 Hz to reduce the overall low-frequency content. This is followed by a compressor having a fairly aggressive 10:1 ratio, which is then followed by the EQ that actually alters the tone of the bass with a slight boost at 175 Hz.
One situation where compressing first usually makes sense is when the signal chain includes a severe distortion effect. Distortion tends to bring up the noise floor quite a bit because of the high gain it applies, so compressing after distortion raises the noise even further. Another time you’ll want to compress first is with an echo effect whose repeating echoes decay over time. When a compressor follows an echo effect, it can raise the level of the echoes instead of letting them fade away evenly as intended.
