If you ever went to use a compressor and just twisted knobs until it sounded good, this series on compressors is for you. in it we’ll look at compressors, limiters, gates and de-essers, then make them work better than you ever thought they could. In Part 3, we’ll look at using a compressor on guitars, keyboards and vocals.
Also available in this series:
- Compression Tricks Of The Pros - Part 1
- Compression Tricks Of The Pros - Part 2
- Compression Tricks Of The Pros - Part 3
- Compression Tricks Of The Pros - Part 4
The Principles Of Compression
The basic principles of compression are pretty much the same for any instrument, but of course there are nuances for each, which is what we’ll soon cover. That said, here’s a brief review:
- Acoustic instruments are usually more dynamic than electric instruments, and therefore need to be controlled more.
- If you set the attack and release times of the compressor so it breathes with the track, the less likely you’ll hear it working in the track.
- The more wild the peaks, the higher the compression ratio should be set. The fewer the peaks, the lower the ratio.
- The more compression you use, the more likely that you’ll hear it, and the more likely it will color the sound.
- A compressor turns into a limiter if the ratio is set to 10:1 or higher.
The type of electric guitar sound that you start with greatly determines the amount of compression that will be needed. For example, clean electric guitars and acoustic guitars usually require a fair amount of compression (6dB or more) since their dynamics fluctuate a great deal, but distorted guitars are already naturally compressed so they don’t require as much as a result. That being said, a little extra compression (2 to 4dB) can make a lead guitar come forward in a mix.
While recording clean electric guitars direct and not through some sort of amplifier simulator is more of an 80‘s thing, sometimes there’s a need for that type of sound.
Since a direct guitar has a huge dynamic range, a it requires some severe compression to keep it under control, usually 10 dB or more. With a guitar that’s amplified, usually the more distorted it becomes, the less compression it requires, although most electric guitars usually require at least a few dB to stay steady in the mix.
As with the bass (which we covered in Part 2), the Ratio control is important to dialing in the right amount of compression on a guitar. Watch the channel meter or input meter on the compressor, and if there are a lot of wild peaks, a higher ratio (8:1) and higher threshold is required. If you just want to round out the sound, use a lower compression ratio (4:1) and a lower threshold, which will give you more compression. Here’s how to set it up:
- Solo the electric guitar. If there are a lot of peaks as you watch the channel meter, set the Ratio at about 8:1 and the Threshold to where there’s enough compression so that you can hear every note. If there aren’t many peaks (like on a distorted guitar), set the Ratio at about 4:1.
- Set the Attack and Release controls so the compressor breathes with the track (as described in Part 1), but also experiment with extreme settings to see what works best.
- Bypass the compressor and listen to the level. If the guitar is louder in bypass, add make-up gain so that the level is the same as when it’s bypassed.
Compressing The Acoustic Guitar
An acoustic guitar can have a lot of peaks, depending upon how it’s played. That means that the ratio should be set higher (usually around 6:1 or 8:1) to keep the dynamics under control. The more compression you add by adjusting the Threshold control, the more forward the acoustic will be in the mix. Sometimes this isn’t what you want though, since an acoustic is used to support the rhythm section sometimes and is meant to blend in rather than stick out. As always, the settings come down to the song, the arrangement, the player, and the instrument, so one setting can never fit all situations. Set up the compressor for the acoustic using the same directions as the electric guitar.
Just like most other instruments, the amount of compression used on keyboards depends on how wild the dynamic swings are. An acoustic piano is inherently much more dynamic than a synthesizer or organ, for instance, and has to be treated differently as a result.
Sampled acoustic or electric pianos don’t have nearly the dynamic range of a real acoustic instrument, since they’re usually processed during recording before you use them, but they still can have some major peaks depending upon the way they’re played. Be aware that the more compression you use, the less realistic an acoustic piano sounds.
Organ and string sounds normally aren’t very dynamic to begin with, but they can benefit from a touch of compression sometimes just to make sure all the notes are heard evenly. This helps to pull it out in front of the mix a bit.
Approach the set up of the compressor on a keyboard the same way as with a guitar. The more dynamic range the instrument has, the higher the ratio needs to be set, and set the attack and release to breath with the track, except in the case of organs and strings. Since they play mostly “footballs” (long sustaining whole notes), a longer release sometimes works best.
The one instrument that greatly benefits from compression more than any other is the human voice, and it’s rare that a vocal doesn’t receive at at least a little compression both during recording and mixing. The reason is that most singers aren’t able to sing every word or line at the same level, so some words get buried as a result. Compression evens out the level differences so you can better hear every word.
The amount of compression can vary wildly on a vocal if it has a lot of dynamic range, sometimes going from a whisper to a scream within the same song, so it’s not uncommon to use as much as 10dB or even more on a some vocals.
Some engineer’s treat a vocal differently during recording than during mixing. When recording, you’re looking to control the peaks to stop an overload rather than to even out the dynamics, so setting the compressor up as a limiter (the ratio control is set at 10:1 or higher) accomplishes the task. In this case, you’re only looking for a dB or two on the loudest peaks of the vocal.
The strategy is quite the opposite during mixing however, because you both trying to even out the dynamics of the vocal so you can hear every word, as well as bring it forward in the mix. In this case, you might need as much as 10dB or more to accomplish the task. Be aware that the more compression you use, the more you’re liking to hear the compressor working, so you have to pay extra attention to the compressor’s settings. This is also a good time to try a few different compressors as well, since some will sound better with higher levels of compression than others.
Here’s how to set up the compressor on a vocal during a mix:
- Solo the lead vocal. If there are a lot of peaks as you watch the meter, set the Ratio to either 6:1 or 8:1, then raise the Threshold until you can hear most of the words at the same level (remember that some may be so different that the only way to fix them is by automating the vocal’s level). If there aren’t any peaks, set the Ratio at about 4:1.
- Set the Attack and Release controls to breathe with the track as described previously, but also experiment with extreme settings. Usually, the approximate settings that you used on any drum will get you in the ballpark.
- Bypass the compressor and listen to the level. If the vocal is louder in bypass, add make-up gain so that the level is equal to the level when it’s bypassed.
- Increase the compression. Does the vocal come out front more? Does it sound too compressed or choked?
Usually loops or samples are already heavily compressed, so be especially careful when adding any additional compression since this can actually change the groove of the loop. Obviously that’s something that we don’t want to happen, but sometimes just a few dB of limiting will allow the loop to sit better in the mix if it has any peaks in the signal.
Set the attack and release controls to breath with the groove of the loop. This is especially important with a loop since an attack set too fast will chop off the front of the signal and make it sound dull. Setting the attack too slow will make the attack especially loud but will cause the rest of the loop decrease in volume. If you set the release too fast, you’ll hear the compressor pumping out of time with the mix, which upsets its groove.
In the Part 4 we’ll look at some extreme examples of compression use, as well as de-essers and gates. 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. You can read excerpts at bobbyowsinski.com.