Caelum Audio Schlap Review

Caelum Audio have been a very well known name among producers looking for fantastic free plugins, and are responsible for free VSTs such as Tape Cassette 2 and FLUX Mini.

Back in 2021, they released a couple of new plugins in their range, this time for a price, including more features and greater depth. One of those plugins was Schlap – a compressor based on old analog hardware, with a new modern interface.

We've been generously given a copy of Schlap to review, and over the past couple days have been putting it to the test to see whether it's really worth your hard earned money.

In this Schlap review, we'll cover the compressor plugin in-depth, and offer our complete, honest opinion on whether we think it's worth it or not.

Schlap (Quicker Review)


Compression Sound, Aggression & Punch
Transient Transparency
Ease of Use
Compression Controls
Value for Money


Schlap is an outstanding re-creation of the dbx160. Incorporating a modern twist, Schlap retains the thickness & punch of the original unit, and includes beautiful, driven, warm and boomy compression, at a low price tag. This is a must have for producers looking for an analog sounding compressor, to add to their collection.


What is Schlap

Compatibility: Win, Mac, iOS, VST, AU, AUv3, AAX, 64-bit
Price: £14.99

Caelum Audio Schlap

Schlap is an aggressive VCA compression/expansion tool that's based on the old DBX160 compressor/limiter. It uses program dependent attack and release, and RMS detection to apply gain reduction, with all the features you'd expect like ratio, threshold, sidechain etc.

RMS detection gives Schlap a clean, slow reacting compression that doesn't destroy transients, and reduces gain on an average of the signal, rather than on the peaks of a signal.

This allows transients to come through the compressor, before gain reduction is applied, and therefore, provides doesn't destroy them, but applies aggressive, pumping compression.

Schlap can also be used as a compressor, expander, gate and limiter, due to the ratio modes available.

You can use upwards expansion with ratios between 0.1:1 – 0.9:1, downwards expansion (gating) with negative ratios, limiting with the inf:1 ratio, and everything in-between applies compression.

Schlap is especially good for drums, and parallel processing. The aggressive styled compression, allows you to really “Schlap” the compressor, giving presence, aggression and a nice room sound, while letting the transients through.

It's also useful on bass, due to the nature of the transient control. It let's the attack through, but clamps down on the bass.

What is RMS Compression?

We're putting an explanation in here, because it's related to how Sclap reacts to your signal, and applies gain reduction.

RMS compression is short for root means squared. RMS compression takes the average amplitude of a signal, and compresses it. This provides a slower compression, allowing transients to cut through.

The compressor only attenuates the signal, when the average of the incoming signal, goes above the threshold that has been set.

RMS compression is often used in limiting because of its transparency. It's also good for vocals due to their less transient nature.

If you want a more subtle compression, use RMS compression.

How Does it Sound?

Schlap sounds aggressive, thick, boomy, and gives a certain pump to sounds. It's especially good for use on bass, drums, guitar and vocals, because it allows transients to come through, then applies gain reduction.

This gives your audio signal a nice thickness, and consistency to it, while keeping all those beautiful, smacking transients.

  • Bass – lets the pluck come through, then pulls it in, giving a nice front and centre effect to it.
  • Drums lets the whack through, then levels it out, giving a boomy, loud and almost expansive sound.
  • Guitar – let's the pluck/pick through, then pulls the guitar in, with an nice front and centre, aggression.
  • Vocals – works well on vocals without too much dynamic range, adds aggression, and brings them front and centre, while levelling out the performance to sound cohesive.

We loved the sound of Schlap and, using it just adds a certain amount of whack to your audio signal. But we wanted a deeper, technical explanation, so we contacted Caelum Audio to find out how it works.

Caelum Audio logo

It takes inspiration from the “compressor/limiter” dbx 160. In this unit, attack times automatically decrease with more gain reduction while release times increase. This means the compressor has limiting properties during periods of high gain reduction as it will be responding quickly to the incoming signal.

It also uses RMS detection instead of the usual method of peak detection which allows any initial transients through the compressor, with less compression which helps them Schlap. 

There were characteristics of the dbx 160 that we didn't like as it can be overly “clicky” on transients so we tuned our algorithm to our taste to maintain the aggressive sound but to remove these unwanted artefacts that the original unit had. Other features such as sidechain filtering and gated ratio options further extend this functionality.


Caelum Audio

Sound Examples

We always think it's best you hear just how the plugins we review sound, so we've left some examples below on different instruments. There are before & afters on each, so take a listen and see what you think!

Schlap really beefs everything up!

Drums (before)

Guitar (before)

Bass (before)

Drums (after)

Guitar (after)

Bass (after)

What Features Do You Get in Schlap?

There's a lot you get with Schlap inside a small plugin, with a simple interface. We'll cover all the features here, and what their uses are. This will help you understand what Schlap is, and whether it's for you.

4 Dynamic Processors in 1

With Schlap you have the ability to change the ratio to alter the dynamic processing to your signal. This allows you to either use Schlap as a compression, limiting, expansion, or gating tool.

There are 4 different modes you can use Schlap in:

  • Upwards Expansion = negative ratio numbers like -10:1
    • This will increase the dynamic range between the high & low amplitude points of your signal above the threshold. Generally makes things sound louder, and more punchy.
  • Downwards Expansion (Gating) = 0.1 – 0.9:1
    • This acts as a smoother gate. It increases the dynamic range between the low and high amplitude points, below a certain threshold, therefore applying a gate-like effect.
  • Limiting = inf:1
    • Limits your signal to the threshold level set. -1 on the threshold will limit your signal at -1db. Schlap is great at transparent limiting.
  • Compression = positive ratio numbers like 10:1
    • Applies extremely transparent gain reduction, when the average of a signal reaches the threshold set.

The compression in general is extremely aggressive and provides a pumping sound. It can be used to add thickness, punch, and accentuate signals using expansion. It also works extremely well at gating drums that require a smoother sounding gate.

Gating was fun to play with on the drums because it gave an almost staccato groove, that would cut in and out, and could be awesome when used creatively on dance music breaks especially.

Program Dependent Attack & Release

(no attack or release on the controls)

An interesting feature of the original dbx160 was the program dependent attack & release. The engineer actually has no control over what these settings can be, rather it's controlled by the amount of gain reduction being applied to the signal.

  • More gain reduction = decreased attack times, while increasing release times
  • Less gain reduction = increased attack times, while decreasing release times

This functionality is what makes it sound so good in parallel, because when you begin to slam a signal, it adds that thick, almost boomy sound to your compression.

When mixed in with the original dry signal, on drums it adds thickness, boom and crunch, while retaining the transients, and tightness.

Exactly how you want most drums on Rock, Hip Hop, and many other genres to sound.

RMS Compression

Schlap uses RMS compression, instead of the more commonly used peak detection found in compression units.

This takes an average of the amplitude, and then applies gain reduction once that average hits the threshold you have, giving a slower response time on the compression's attack.

Using RMS compression gives Schlap the ability to allow transients to cut through before being clamped.

Therefore, it makes the compressor great for drums, bass, guitar, and anything where you want to preserve the transients, rather than control them. Peak compression will react to transients straight away, squashing them, and sometimes destroying them.

Not all peak compressors do this, and it entirely depends on which compressor you use for your mix.


schlap sidechain compression

In Schlap there are also options for sidechaining, and with it being an extremely aggressive pumping compressor, we'd recommend using it for sidechaining over your usual sidechain plugin, when you want a heavy pump.

The sidechain is useful because it also has a separate filtering module which can be used even without an input.

This allows you to filter compression, to affect certain frequencies, acting like a multiband minus the bands.

The filter becomes especially useful when you don't want to affect your kick drum. Schlap can make things very boomy, and sometimes it's a bit too much for a large, already sub heavy kick.

Fantastic Presets

Inside Schlap, you'll also get 18 fantastic presets that will each give you a good starting point depending on your signal.

The basic drum bus will absolutely “Schlap” your drums beyond belief.

There are also some great gating presets, that will help you clean up messy audio in a smooth way.

New Improvements From The Hardware

Finally, the team at Caelum Audio have altered the original dbx160 sound slightly, to remove the clicking artefacts you would get from the original.

This allows for the same style and aggression of the original unit, but takes away the nasty bits you wouldn't necessarily want.

They've also included new features such as the sidechaining, filtering options, and the ability to use Schlap as an expander, or gate – making it even more versatile.

The Technical Stuff

Below we'll talk about all the technicalities of Schlap – what you'll need to run it, how hard it is on the CPU and how the user interface is.

CPU Usage

Schlap is very easy on the CPU, and won't give you any problems when using it – even with the beautiful graphics for gain reduction provided.

It's a lightweight, easy-to-use compressor that will give you an aggressive sound in a matter of moments.

You can multiple instances of Schlap with no worry for your CPU!

User Interface (GUI)

The user interface is super simple, clean and easy to use. Everything is where you'd expect it to be, and it makes sense in terms of workflow.

You have input metering, and output metering, as well as a gain reduction meter in the middle of the plugin.

This is really easy to understand, and shows you exactly how the compressor is working, by displaying the amount of gain reduction in red, and the compressed signal in a grey/white colour.

The only qualm we have with the user-interface (and it's a really minor thing), is that the metering doesn't show when the plugin is clipping.

We understand that this is because Schlap will also limit the signal when it gets too hot, but it would be nice to see how much in the red you are, without having to use an extra metering plugin.

Other than that, for £14.99, you really can't complain. It's a great compression tool.

System Requirements

To run Schlap you will need:

  • A 64-bit DAW host
  • Windows 7 or higher
  • Mac OS 10.19 or higher
  • iOS 11 or higher

How Much Does Schlap Cost?

Schlap is exceptionally cheap for such a great-sounding, analog compression unit. It's £14.99 for a license. You can also try Schlap out, download the demo, before purchasing. We always recommend you try before you buy.

In terms of price, this compressor plugin is one of the cheapest we've seen around, and still has an incredible build & sound quality to it.

It provides warmth, aggression and drive, for almost half the price of a Waves plugin and a fraction of a UAD plugin.

The UAD dbx does have the edge on Schlap, but if you're in a toss up between the Waves and Caelum Audio version, the difference is negligible, so save yourself some cash and get Schlap.

Is Schlap Worth It?

Yes Schlap is worth it. It's a fantastic sounding, aggressive compressor, that will help you to beef up anything from drums, to synths, bass, guitar and vocals. It's best used as a parallel compressor for punch.

We would highly recommend getting Schlap if you're on a budget and want some analog-sounding gear.

It does a pretty great job of getting the sound of the dbx160 in a digital form. It's not 100% accurate, but then again, no “inspired by”, or “emulation” is.


Schlap (Quicker Review)


Compression Sound, Aggression & Punch
Transient Transparency
Ease of Use
Compression Controls
Value for Money


Schlap is an outstanding re-creation of the dbx160. Incorporating a modern twist, Schlap retains the thickness & punch of the original unit, and includes beautiful, driven, warm and boomy compression, at a low price tag. This is a must have for producers looking for an analog sounding compressor, to add to their collection.


Schlap is fantastic. It's great to use on drums, and the new additions to a classic unit are extremely welcome. It has a nice interface, a price that won't break the bank, and will give you incredible-sounding, punchy compression in moments.

Best used as a parallel aggressor, on drums, or on bass. However, you can use it on anything that needs something a little extra. We liked it so much, we even included it in our best compressor plugins list.

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