Compression Tricks Of The Pros

If you ever went to use a compressor and just ended up twisting knobs to try to make it good without really knowing why, this series on compression is for you. In it I’ll try to give you a few tips to make compressors, limiters, gates and de-essers work better than you ever thought they could. In Part 2, we’ll discuss compression on the drums and bass, and a neat trick from New York City.

Also available in this series:

Compressing The Drums

It would be great if every drummer hit every beat on the kick and snare with the same intensity, but unfortunately that doesn’t even happen with the best drummers on the planet. When the intensity changes from beat to beat, the pulse of the song feels erratic, since even a slight change in level can make the drums feel a lot less solid than they should be. Compression works wonders to even out those erratic hits and helps to push the kick and snare forward in the track to make them feel more punchy. Let’s take a look at how to do that with the drums and bass.

The Compression Technique

Before we get into specifics, here’s the technique for setting up a compressor. Regardless of the instrument, vocal or audio source, the set up is basically the same.

Start with the attack time set as slow as possible, and release time set as fast as possible on the compressor.
Turn the attack faster until the instrument begins to sound dull (this happens because you’re compressing the attack portion of the sound envelope). Stop increasing the attack time at this point and even back it off a little so the sound stays crisp.
Adjust the release time so that after the initial attack, the volume goes back to at least 90 percent of the normal level by the next beat. If in doubt, it’s better to have a shorter release than a longer one.
The more wild the peaks, the higher the ratio control must be set, so increase it until the sound of the instrument or vocal is pretty much the same level throughout.
Bypass the compressor to see if there’s a level difference. If there is, increase the Gain or Output control until the volume is the same as when it’s bypassed.

Tracking Versus Mixing

Generally speaking, most engineers won’t compress much, if at all, during tracking, since anything you do while recording can’t be undone later. That said, some engineers like to limit the instruments a little (only by a dB or two) just to control the transients a bit. A compressor becomes a limiter when the ratio is set to 10:1 or more. If you choose to do this, make sure that the limiter kicks in on only the highest peaks. If it’s limiting constantly, it’s probably too much and you might regret it later. Decrease the threshold control so it only limits on the occasional transient.

Compressing The Kick And Snare

The biggest question most engineers have when compressing either the kick or snare is “How much is enough?” This depends first and foremost on the sound of the drum itself and the skill of the drummer. A well-tuned drum kit that sounds great in the room should record well, and a reasonably good drummer with some studio experience usually means that less compression is needed because the hits are fairly even. Even a great drummer with a great sounding kit can benefit from a bit of compression though, and as little as a dB or two can work wonders for the sound. With only that amount, the setup of the compressor is a lot less crucial, especially the attack and release.

Sometimes you need the kick or snare to cut through the mix and seem as if it’s in your face, and that’s when 6 to 10dB or so does the job. It’s here that the setup of the compressor is critical because you’re imparting its sound on the drum. Make sure you tweak the attack and release controls as above, and even try a number of different compressors. You’ll find they all react differently, even with the same settings, so it’s worth the time to experiment. Remember: if the attack is set too fast, the drum will sound less punchy, regardless of how much compression you use.

Compressing The Room Mics

The room ambient mics are meant to add the “glue” to the sound of a kit, and can really benefit from a fair amount of compression, which means anywhere from 6 to 10dB. In fact, many mixers prefer the room sound to be extremely compressed, with way more than 10dB being the norm.

The problem is that the more compression you use, the more the ambience of the room is emphasized. That’s okay if you’re recording in a great sounding room, but if it has a lot of reflections and the ceiling is low, you may be emphasizing something that just doesn’t add much to the track. One trick is to actually set the attack time so it’s much shorter than usual to cut off the sound of the initial drum transient, then tuck the room tracks in just under the other drum tracks.

Note that regardless of how good the room mics sound, the more of them you use, the less space there will be for the other instruments in the track. The more instruments there are, the more you’ll have to back them off. Sad but true, but unfortunately, there’s only so much sonic space to any mix.

The New York Compression Trick

There’s a great trick that really punches up the sound of the entire drum kit without adding more compression to the individual tracks. I call it the “New York Compression Trick” because when I was starting out, every mixer in New York used it on their mixes. Mixers every use a variation of it these days so it’s not that exclusive to New York City any more, so we’ll can call it by it’s more academic name - parallel compression.

The trick centers around a drum subgroup that has a compressor with some rather extreme settings. Once the the subgroup is set up and compressor is kicking, the subgroup is gently raised until it’s just barely heard against the original drum mix. If you want the drums punchier, just add more of the parallel compression subgroup level.

Just a little waring in advance; the sound that you get out of the drums when using parallel compression is addicting, and chances are that you’ll want to use it on every mix (and there’s nothing wrong with that if you do). Here’s how to set it up.

Assign the drums to separate subgroup. If the drums are already bussed to one, insert a second.
Insert a stereo compressor to the subgroup channel and set it so there’s about 10dB of compression and the Attack and Release breathes with the track as illustrated above.
Raise the fader level of the subgroup with the compressor until it’s tucked just under the present rhythm section mix to where you can just hear it. Can you hear the sound get punchier?
For an even greater effect, EQ the subgroup with +6 dB at 10kHz and +6 dB at 100Hz.
As an alternative, try adding the bass guitar to the new subgroup mix as well as the drums. Sometimes this can really glue the track together.

Compressing The Bass

Most basses inherently have notes that are louder or softer than others depending upon where they’re played on the neck of the instrument. This is especially noticeable on a bass played with a pick instead of fingers. Some notes just roar while others might get lost, which is why at least some compression is usually necessary on the instrument. On the other hand, there are some mixers that build their mixes around the bass and want the level to be virtually the same throughout the song, so they’ll compress the bass heavily to make that happen.

The Ratio control is important to dialing in the right amount of compression on the bass. Watch the channel meter and if there are a lot of wild peaks, a higher ratio (10:1 or more) is required. If you just want to round out the sound, use a lower compression ratio (2 or 4:1).

Many mixers prefer that the bass have no dynamics at all in order to keep the mix solid and punchy. To accomplish this, increase Ratio control to 12:1 or more and increase the threshold control until there’s between 6 and 10dB of compression or more.

Remember that the settings for a miked bass amp might be different, depending upon how distorted it is. The more distorted, the more naturally compressed it will be and the less benefit it will receive from any compression that you apply.

In the Part 3 we’ll look at some typical compression schemes on other instruments not in the rhythm section. Some of the above material comes from my book Mixing And Mastering With IK Multimedia’s T-RackS, and my upcoming book The Audio Mixer’s Bootcamp.

Compression Tricks Of The Pros - Part 2