Difference between Compressors

[Negoba]

I have heard people say different compressors have different sounds or characteristics. I understand the basics of compression but I don't get how they sound different. Threshold is threshold, ratio is ratio, makeup gain is makeup gain. What am I missing?

And I guess then what are good free and pay examples of the different types / sounds of compressors that might help a newbie understand?

[HOTF]

I think you're perspective comes from the digital world. different types of compressors used different technologies to process the sound each technology had it's characteristics.


Tube Compressors: Also known as Variable-Mu or Vari-Mu compressors, these are the oldest types of compressors. They use tube technology, which imparts unique, saturated sonic characteristics to any signal that you put into it.

Optical Compressors: Sometimes referred to as ‘opto’ compressors, they convert audio into light, applying compression whenever it hits a light-sensitive resistor. They’re slower compared to other types of analog compression.

Field Effect Transistor (FET) Compressors: These came about when audio units started replacing large tubes with smaller transistors. FET compressors’ slowest attack time tends to be faster than other compressors, such as a Variable Mu.

Voltage Controlled Amplifier (VCA) Compressors: These offer the most aggressive gain reduction, making them a good choice if you’re trying to keep in check any loud transients or spikes in volume. VCAs are generally suited to your workflow if you’re trying to tame any intense peaks in your track due to its snappy response

Some plugins try to emulate those characteristics and other embrace the clean and transparent behaviour of digital.

[stoopicus]

Yep, what HOTF just said. Nothing really to add to that. You can easily tell the difference in hardware, and the software compressors emulate that.

[saint_william]

I have also been wondering about this, and different EQs, how they can be different.

May I ask what a good free examples of each would be to do some side by sides. Compressors and EQs if you’re feeling generous.

I know this topic has been covered a million times - and I watched a million videos just looking for a clean way to test it out for myself with some guidance.

Thanks

[Scrubbing Monkeys]

In addition to the above ....place a scope after the compressor. Start with a one loop of a snare hit. Watch what happens as you adjust the controls. Then try a full beat....then a bass groove. Notice how the transient attack activates the compressor and how it holds down the signal through the release time. Just a way to get a visual idea.

[stoopicus]

May I ask what a good free examples of each would be to do some side by sides. Compressors and EQs if you’re feeling generous.

One free example that I can think of that is both aggressive like a FET and also (to me) sounds like it adds some saturation (like a tube) is d16's Frontier limiter. It automatically adds makeup gain for you so the Threshold control can be pretty aggressive in tonal changes.

They claim it can be used as a transparent limiter but in practice I think it definitely adds a bit of color at anything but minimal settings. YMMV though.

If you are looking for specific examples, there's a number out there that emulate very famous compressors/limiters like the 1176 and LA-2A.

[Negoba]

So it looks like the usual digital compressors basically work in the same way as VCAs.

Opticals have an inherent attack parameter in their design.

Tube adds saturation and perhaps some low end.

Still trying to wrap my head around what makes something more aggressive or not.

[stoopicus]

Still trying to wrap my head around what makes something more aggressive or not.

Short attack with high makeup gain would be how I think of it.

[swilow11]

So it looks like the usual digital compressors basically work in the same way as VCAs.

Opticals have an inherent attack parameter in their design.

Tube adds saturation and perhaps some low end.

Still trying to wrap my head around what makes something more aggressive or not.

Short attack and short release, low threshold and high ratio. Dynamic range gets squashed and the waveform takes on characteristic similar to distortion/saturation. In fact, listening to the effects of distortion and saturation on drum loops is a good way to understand what compression can sound like (obviously minus the added harmonics).

I studied audio engineering years ago, and one thing I took on was the idea of setting the compressor to basically mirror the 'real world' envelope of a sound. For a pad, slow attack, slow release, for drums quick attack and quick release. This creates more transparent compression, at reasonable ratios at least. It wasnt until I started seeing what happens at more extreme settings, and inserted after thins like reverbs or delays that I really came to understand how compression can also be a sound design tool. Although in general, I prefer to use them as a standard volume automation device.

[imrae]

I have heard people say different compressors have different sounds or characteristics. I understand the basics of compression but I don't get how they sound different. Threshold is threshold, ratio is ratio, makeup gain is makeup gain. What am I missing?

Most of the other key controls

Attack, release, and knee are much less well-defined. They can have different shapes and ranges. "Auto" release may be a consequence of the hardware physics but can also be implemented by combining multiple gain-control signals. Another interesting shape parameter is a GR limit; somewhere above threshold the transfer curve may return to a 1:1 ratio.

Kotelnikov is a great free compressor for exploring how program-dependent release can work; it gives a lot of control over this without too many knobs. Then the paid upgrade to Kotelnikov GE adds GR limiting and some more exotic stuff; have a look at the user manual!

[roman.i]

I have heard people say different compressors have different sounds or characteristics. I understand the basics of compression but I don't get how they sound different. Threshold is threshold, ratio is ratio, makeup gain is makeup gain. What am I missing?

And I guess then what are good free and pay examples of the different types / sounds of compressors that might help a newbie understand?

You are missing curves - attack, release, compression curves, and other analog component behavior.
In digital compressors they are usually linear or logarithmic.
Analog compressors may have unexpected behavior, for example in 4:1 ratio it may start compressing with 4:1 but after few db of reduction compress 2:1, which may work really good on some material.
Ex. Over the years, L2A proven to work on vocal and if that is what you need then you can use an emulation of L2A, instead of the "boring" standard compressor.

[Negoba]

Thanks folks. I assumed attack and release was just in ms and that was it. I also assumed ratio was a constant. I learned on the protools stock compressor with the usual video representation of the response and assumed that everything worked pretty much like that.

More learning to do. Appreciate the help.

[Uncle E]

Tube adds saturation and perhaps some low end.

Most of the sought after hardware compressors clip and saturate in some way, even the tube-less ones. It's the entire premise of the Distressor. Clipping short transients first allows the compressor to respond more smoothly and not be pushed as hard or as erratically.