Not understanding compression fully (Logic Pro)

[isuckatproducing]

Hi,

So I'm using a Logic's compressor on let's say a bassline, and even with aggressive settings there are still sometimes some peaks in volume. The only way I can combat it is to turn on the limiter knob inside the compressor.

But isn't compressor supposed to squash these peaks in the first place?

[Dalle]

Compression can do many things. If the attack setting is slow enough, transients will get through and you can actually be increasing dynamic range.

[ampetrosillo]

You see, you have a ratio control (eg. 4:1, 8:1, etc.), you have an attack control (eg. 10ms), you may have a choice of feedback or feedforward compression. Feedback compression will always be "inferior" at squashing peaks, but this is not the main issue. As I said, that ratio control only means that you're lowering everything over the threshold (and also below if the release stage is still active) by 4:1. And you have an attack which is non-zero. That means that peaks *will* get through, and even when the compressor is fully active (after the x ms of the attack stage) the compressor will only be lowering the volume by a certain ratio which is not infinite. So that's why you need a limiter. But really, you only *need* a limiter at the master bus, also called the mixbus. The mix should never clip. Anything before the master bus may well "clip" (it doesn't, in any modern DAW). You may still use a limiter on single tracks if you like the effect.

[jamcat]

Anything that happens between triggering the threshold and the compressor kicking in after the specified attack time is going to get through uncompressed. And then, once compression kicks in, it reduces the volume only above the threshold, and only by the chosen ratio starting at the threshold. Then, when the input drops below the threshold, the process starts again.

So if you have it set to 3:1, a 6dB jump in volume above the threshold will still jump 2dB above the threshold, after the compressor kicks in. A limiter is also just a compressor, but the attack time is non-existent (usually aided by looking ahead), and the ratio in very high, typically 20:1 or greater, to the point where it is effectively ထ:1.

So if you have to resort to using a limiter to get the results you want, that just means your compressor wasn't set steep and/or fast enough.

But also, you should really be asking yourself at that point why you want that much compression. It's a common mistake made by beginners to rely on squashing everything rather than setting proper mix levels and balancing the dynamic performance of a song. A song where everything is flattened and equally loud at all times doesn't age well.

[isuckatproducing]

I've seen a lot of producers doing this, the issue is that some synths might be "unstable" and gain much volume at certain key, if that makes sense. Or some synths might generate some weird "click" or something.

[jamcat]

Yeah, what you're talking about is transients that are probably the product of resonant peaks. There's not much you can do about that under normal compression since they come on so hard and fast.

In those cases using a limiter in conjunction with a compressor is really common. It's done a lot on drums and guitars, too. The standard trick is to use an 1176 in front of an LA-2A. The 1176 is set to limit (fastest attack, 20:1 ratio), but the threshold is quite high so it's only grabbing the peaks that really jump out. Then it hits the LA-2A with gentle to moderate compression, and it's not working too hard because the sharp transients that would otherwise send it into over-compression have already been killed.

It sounds like that's probably what you need to do, and what you are effectively doing already by engaging the limiter.

[roman.i]

Hi,

So I'm using a Logic's compressor on let's say a bassline, and even with aggressive settings there are still sometimes some peaks in volume. The only way I can combat it is to turn on the limiter knob inside the compressor.

But isn't compressor supposed to squash these peaks in the first place?

This means the attack is not fast enough.

[isuckatproducing]

Or should I just slap a limiter instead?
I also just got a UAD DBX 160 compressor but I suppose it's for different type of stuff?

Damn I was always scared of compressors/limiters because it's easy to think you did it well while in fact you mess up the signal!

Always have an issue with finding proper attack/release for multiple sounds, hard to do by ear. (for me).

[roman.i]

You should first listen, then identify a problem, and think of a tool that can fix the problem.
Don't just slap the compressor for no reason.

Limiter is a better option than a compressor if you just need to chop some peaks.
In drums maybe a transient shaper (Logic's envelope shaper)

[isuckatproducing]

You should first listen, then identify a problem, and think of a tool that can fix the problem.
Don't just slap the compressor for no reason.

Limiter is a better option than a compressor if you just need to chop some peaks.
In drums maybe a transient shaper (Logic's envelope shaper)

I'm not sure how env shaper is supposed to handle random "pops" in volume? I've struggled with them especially with ES2 synth, where it would sound stable and then suddenly boom +4DB peak.

[roman.i]

You should first listen, then identify a problem, and think of a tool that can fix the problem.
Don't just slap the compressor for no reason.

Limiter is a better option than a compressor if you just need to chop some peaks.
In drums maybe a transient shaper (Logic's envelope shaper)

I'm not sure how env shaper is supposed to handle random "pops" in volume? I've struggled with them especially with ES2 synth, where it would sound stable and then suddenly boom +4DB peak.

Why it has pops in the first place? It shouldn't.
Try increasing buffer size in audio settings.
If this is the sound, then limiter is the better solution.

[isuckatproducing]

You should first listen, then identify a problem, and think of a tool that can fix the problem.
Don't just slap the compressor for no reason.

Limiter is a better option than a compressor if you just need to chop some peaks.
In drums maybe a transient shaper (Logic's envelope shaper)

I'm not sure how env shaper is supposed to handle random "pops" in volume? I've struggled with them especially with ES2 synth, where it would sound stable and then suddenly boom +4DB peak.

Why it has pops in the first place? It shouldn't.
Try increasing buffer size in audio settings.
If this is the sound, then limiter is the better solution.

Don't remember as I'm not touching ES2 anymore.
Thanks for reminding me of "Logic's envelope shaper", I had plugins doing same thing which I just trashed, less is more.

Which limiter would you suggest for basses and similar synths, Adaptive Limiter or normal one?
Also I know every sound is different, but any starting point settings and what to look for?

I'm doing Techno so taming these peaks I believe is important to get a louder mix in the end.

[jamcat]

Try switching to classical or jazz for a smoother sound.

[aciddose]

This is probably a misunderstanding about the definition or proper way of thinking about a "compressor".

Imagine your audio waveform is an inflatable boat. It's only half-full, so sitting a bowling ball in it will pinch it flat in that spot with maybe only a centimeter of air under the ball. A compressor is acting like placing differently weighted balls in this inflatable boat you call your audio track. If you place a ball of yarn, it barely compresses at all, this is a "low ratio", while a lead weight crushes it nearly flat "high ratio".

(In this example, the ratio would be air pressure vs. weight of the added mass.)

A compressor is defined as "low ratio" and a limiter is defined as "high ratio" essentially. They're both in essence the same thing just with different parameters. There are many different variations of techniques (envelopes, look-ahead, multi-phase rectifiers, filters, nonlinearities and others) that can create different types of compressor/limiters.

If you're using a 1/2 ratio compressor, no matter what you do even in absolutely ideal circumstances the peak level "attack" of your waveform will only be reduced by strictly less than 50%. You might get numbers like 72% or such depending upon frequency, hysteresis and other properties of the compressor and input waveform.

I personally prefer to distinguish compressor/limiter not strictly based upon ratio but rather design: To me, a compressor uses something like 1-x (common analog design), whereas a limiter uses 1/x (common digital design.) The compressor is taking the envelope and reference volume/threshold and applying a linear subtraction step. The limiter would be applying a non-linear division. Since the application of the result is generally a multiplication the effect of using subtraction produces a non-linear effect on the dynamics curve (soft curves) and using division produces a linear effect (straight lines.)

This is a bit hard to explain clearly, but, addition/subtraction and multiplication/division are in essence the same operations in inverse. One "undoes" the other, they're both reversible by the other. This is basic middle-school level algebra. For whatever reason such a mathematical distinction wasn't made when these terms were invented and we often will run into the distinction interpreted as referring to ratio instead.

If we do go by the common meaning of compressor/limiter, they're essentially the same thing just as addition/subtraction or multiplication/division are!

https://en.wikipedia.org/wiki/Dynamic_range_compression
From the wikipedia article:

Compression and limiting are identical in process but different in degree and perceived effect. A limiter is a compressor with a high ratio and, generally, a short attack time.

[aciddose]

Somewhat incidentally,

the LA-2A compressor uses a "limit" switch which influences the ratio between feed-forward and feed-back signals used to generate the envelope.