Last time around we looked at the basic controls of the compression effect, a core part of dynamics control in audio. This week we’ll look at some specialised variants: Limiters, Expanders, Gates, and Multi-Band compressors. Then… more listening!
Limiters are in essence compressors with very high ratio settings – as high as “Infinity:1”!
The primary use of a limiter is not to manipulate, change or restructure a signal’s dynamics, but rather to contain them! It limits the peak of the signal from exceeding a predetermined setting. This is usually done to prevent overloading or clipping a recording device/mixer or P.A. system. A good limiter has no sound of its own. You shouldn’t even know it’s on. The only way you would know, is if it was turned off and you heard the clipping and distorting that it was protecting you from. Past that, once turned on, you would simply miss the clipping and distorting, and nothing more. Limiters are (or at least should be) the ultimate silent partner.
Note: Limiters are one of the key ingredients used AND abused in mastering studios.
As you know, limiters have the same controls as compressors, so we don’t need a repeat. However, since limiters can be used for compression as well as their main function of, well, limiting dynamic range and preventing clipping, I thought it would be a little fun to have a few clips showing off limiters used in a musical fashion. These following clips are NOT set up with extreme settings, but rather “real life” settings. I hope you enjoy them!
Country chick’n pickin’ lick, bridge pickup, x2 – Original, then limited.
Longer country chick’n pickin’ lick, bridge pickup x2 – Original, then limited.
Long chord comp x2 – Original, then limited.
The limiter was used lightly for the purpose of:
- Bringing up overall volume
- Prevent clipping while boosting the overall level
As a side effect of the second point above, a small amount of smoothing out and sustain was introduced. Not enough to alter the sound mind you, but just enough to glue it all together. (That’s the mastering engineer in me talking!)
- Threshold: -9. Yep that’s all I used.
- Ratio: 4-1 – the standard for guitar licks. Just enough to smooth everything out.
- Attack: 20ms
- Release: 50ms
- Makeup gain: I set it to “auto”… I’ll admit, I didn’t feel like doing the math!
- Digital clipping prevention: set to .02 from absolute digital zero. (Just for extra clipping prevention!)
Expanders and Gates
Expanders are simply compressors in reverse. While a compressor tries to bring the bottom and top of a signal together; an expander does just the opposite. Hence the name. Actually, if you notice, all of these names are actually very self-descriptive once analyzed!
Expanders are used primarily for noise reduction, since this expansion process pushes the noise floor well below audible thresholds.
Gates on the other hand, serve the same purpose but use a, well, gate control to cut off a signal or noise at any desired set point, removing the quieter section. The cut is not transitory and smooth, but rather abrupt, and instantaneous. In addition to noise reduction, gates therefore are also used to manipulate sounds creating gated drums or gated reverbs, where a portion of the sound (beginning or end) is chopped off. The result is a very unnatural sound with a very sharp start or cut off. There is no ramp up, or decay (depending if it is used at the start or end).
Used properly, gated sounds command attention and can actually be frightening because of their sharp on/off characteristics! The 80’s music had great examples of gated sounds like the artists Devo, or Phil Collins. Of course, as with anything new, gating got overused and saturated to the point that now it has a very dated 80’s “stigma” attached to it. Sad, since used properly it is a very dramatic effect. But, I digress…
Single-band and Multi-band
This is an area that could easily fill many essays and still not fully do this particular topic justice, but we’ll distill it down to the parts we need right now!
Single-band compressors and limiters process the whole signal at once. They encompass the whole frequency range of the source signal and compress or limit that entire range. Thus, single band. This is the most popular and widely used type of compressor/limiter. All the examples in Dynamics, Part 1 were single-band compressors.
Multi-band compressors and limiters on the other hand, break the incoming source signal into 3, 4, 5, or even 6 independent frequency bands. (If you’re a little in the dark about all things frequency; this might be a good time to look into the frequency series. OK, end of sales pitch!)
The individual frequency bands are then able to be compressed, or limited individually with different amounts of processing for each band. If you remember, frequency waves behave differently and travel at different speeds; thus if we keep that in mind, then we realize that the compression required to process the low frequency spectrum of a sound will likely be entirely different than what is required to process its mid band, high band, or other frequency bands. In short, this provides tremendous fine tuning control over a sound.
Such fine control is offered as a matter of fact, that many engineers use multi band dynamics processors as sophisticated equalization (EQ) units. They are able to control the dynamics of each portion of sound exactly as they want, and as a simultaneous consequence of said action, use that as a means to accentuate or diminish those same parts in much the same manner an EQ would be used. Pretty nifty!
This assignment will be the easiest one I have given in all my articles!
It will require you to only listen.
Listen many times, listen often, but listen. This is all I want from you. (There will be questions down the road! Fair warning…)
The lesson goal is to hear the different effects of compressors and limiters. I want you to be able to discern a compressed sound from an uncompressed sound. In order to be able to accomplish that, you need to know what to look for! Sometimes it will be impossible due to the subtle and proper use of compression, but mostly there are tell-tale signs and side effects that give away that the signal is compressed. Here are some obvious and extreme things to look for:
- All parts of a sound are at equal volume. e.g. A singer’s breath between phrases is as loud as the singing!
- Background noise is unnaturally loud. Too loud in proportion to the source signal!
- You can tell that a sound is trying to waver normally with regards to volume, but you can actually hear something choking it; or better yet clasping it and keeping it at a consistent volume. This is dead giveaway of over-compressing!
- The most overlooked sign is this: Ear fatigue. You experience ear fatigue way, way too early. That is a clear sign that your brain has to work extra hard to process the excessive and unnaturally dense information.
This last one may seem like a joke, but don’t laugh! This has been documented and is at the forefront of the “volume wars” in the CD mastering fields! The consensus being that CDs are being mastered with WAY too much compression which makes them almost unbearable to listen to. Any types of natural flowing dynamics have been eliminated; what is left is all peaked out at one volume. Very tiring to the ear. Check your CD collection, and start paying attention to some of these details. You’ll be surprised to find things you simply ignored before, or just passed off as a property of that particular CD.
There are many more tell-tales, but this is enough to get you analyzing. Also I am sure you have noticed by now that compression is a powerful weapon. Used correctly and you obtain control. Used incorrectly, or simply overused, and you have sonic anarchy! And make no mistake; we have ALL overused them at on time or another!
All the samples are presented unprocessed and processed. The clips provided were created in my studio for the sole purpose of demonstrating compression. As always keep in mind that extreme settings were used to highlight the effect. You normally wouldn’t use anywhere near as much compression. If you did, the 4 things above to look for would stick out in the most annoying way!
Once again, really pay attention to the details we discussed. Soon it will be an automatic habit to be able to spot a compressed signal; regardless of whether it was done properly or not.
Clean Guitar Examples
Clean punchy compression. 4:1 ratio, gentle threshold.
Pros: Brings the chord to life. Full, Punchy, Bright.
Cons: Decay noise starts to become audible at the end.
Heavy compression. 6:1, low threshold (most signal gets nuked)
Pros: Usable as a deliberate special effect only.
Cons: EVERYTHING is audible. (Finger noise, line noise, signal noise.)
Clean, punchy compression. 4:1 ratio, medium threshold.
Pros: Loud crisp and clean. Makes the single note riff stand out!
Cons: Could get a little fatiguing after a while. (Too mush sugar and all that stuff!)
Heavy compression. 8:1, very low threshold (all signal gets nuked)
Pros: Changes the sound drastically. Very sludgy and grungy. Great for loose, greasy funk jams where a dirty sound is needed without using “distortion” effects.
Cons: No articulation is left. Everything is smeared. So much compressing, that actually the sound is quieter! (No where left to go, it collapses on itself) And the noise, well, as you know… EVERYTHING is brought up!
Clean light compression. 3:1 ratio, medium threshold.
Pros: Brings out the lightly tapped parts. Crystal clear.
Cons: None. A good example of proper use.
Too much compression. 4:1 ratio, medium threshold again.
Pros: None. This is to show how even slightly overdoing it can damage things.
Cons: Excessive compression brings out finger noise that distracts from the passage, as well as amplifying noise. Passage gets sloppy sounding. Note… this time the jump from “just right” to “yuk” was not that much! A lesson to be learned.
Slap Bass Examples
Dark compression. Ratio 6:1, threshold low, and release set slow to keep signal squashed.
Pros: Aggressive yet soft, blunted sound. The slow release saw to that.
Cons: Can easily get buried in a dense mix. Notes get a little blurry.
Clean LOUD compression. Ratio 4:1, threshold set high, attack set slow, release set medium.
Pros: In your face, bright and punchy. (Attack and release saw to this!) Great for dense mixes.
Cons: As with all compression; everything is amplified, so ear fatigue could happen if you were to listen to this by itself. However, in a dense mix: MAGIC!
Multi-band compression. A rather obnoxious example of what can be done when you compress frequency bands individually.
Pros: This is a subjective area. How you use this to “shape” things is up to you.
Cons: Once again, entirely subjective.
Medium compression. 3:1 ratio, medium attack and release.
Pros: Good way to even out the kick drum beats and add a “cut”.
Bright multi-band compression. 2:1 ratio. Multi-band with heavy boost on the 2-3 kHz range.
Pros: Great way to manipulate select frequency bands for brightening the snare, and hearing its springs more.
Cons: A little too bright… but it was done on purpose to show off a little!
Hollow multi-band compression. Heavy emphasis on the frequency band between 507Hz – 3.3 kHz. This resulted in a loud, hollow haunting snare with LOUD springs. Once again, just a demo to show what can be done.
Pros: Can dial in unique sounds for unconventional music.
Cons: None really. Just don’t use it in a soft tender “ballad”. Or… maybe you should!?
Last note: I hope you noticed the dynamics effect that was on the snare yet deliberately NOT mentioned!
Ok, Ok… there was a gate on the snare. See, it doesn’t always have to be an 80’s effect!
Bonus mystery question
As you saw, we discussed what compression can do for you. As we all know, there is no free lunch, and everything has a price. In this case there are side effects to using compression mentioned above. Still though, most recorded music in all styles uses compression effects; and quite liberally I might add!
However, there is one hold out. This is a two part question:
What style of music uses no compression; or at best only a tiny bit, just to tame peaks or clipping?
Concerning this “style” of music:
If any dynamic processing is used at all; then what type is used… single band or multi band, and why?
We’ll answer this next time!
Remember you can save the examples above to train with whenever you like – just right-click and choose “Save As…” to save them to your computer or MP3 player.
Next time we’ll be making some noise with Distortion in all its forms and flavors! Hit one of the buttons below to subscribe so you won’t miss it.