Overview: Simple Guide To Understanding Compression

Random picture of some compressors that I took at Konk Studios in North London. I put these pictures in so people don’t get scared at the idea of reading all that text. Reading stuff is old school, analog, I like it. Before you ask: 1176 Rev F/G, EL8 Distressors, and DBX 160s.

Oh hello there! I do hope you are keeping well. Given that a lot of us may well have a bunch of spare time on our hands at the moment, I thought I’d post up an overview of my ‘Science of Art - Guide To Compression’ series. If you’re home struggling to fill your time and are trying to demo some stuff or produce your own music, I thought it might be useful. I’ll be adding to it over the next few days/weeks.

If you’re a complete beginner, I should preface this guide with what a compressor actually does, which can be simplified into two main points:

• It turns the loud bits of the audio down and the quiet bits up so that part is more 'even' in dynamics. This makes things sound more 'upfront' and less in the background (in the context of a mix).

• Compressors often add some pleasant distortion/harmonics, so they colour the sound - often in a cool or dramatic way.

…and you can use them for either or both reasons. That's why people get can obsessed with different compressors - they can sound very different to each other and have their own personalities and signature sounds.

Onwards - here are the five parts that are currently available, along what they cover:

• Part 1 - We cover the first of the basic controls of a compressor: the Threshold, Ratio, Attack and Release.

• Part 2 - The Knee control (and how it’s different from the Attack Time), Gain Reduction and Make Up Gain.

• Part 3 - Side-Chain Compression, the Side-Chain Input, and Compression Metering (Peak vs. RMS)

• Part 4 - Find the ‘perfect’ compressor settings - every time. It's a method I was shown years ago and it's pretty cool.

• Part 5 - Serial Compression - exactly what’s going on, and why you shouldn’t be too scared of using multiple compressors in series (one after another).

In the future, I’m going to add posts on other subjects: ‘parallel’ compression, ‘master bus’ compression, the difference between using a compressor on single/instrument tracks vs, the master bus and during mastering, the difference between various compressor types (optical, FET, etc), the settings on famous compressors and their common uses: the 1176, LA2A, LA3A, DBX 160, the SSL Channel Compressor and the venerable, SSL Bus Compressor. And other stuff too.

That's all for now. If you need any clarification on any particular aspect, or have a topic that you’d like me to do a post about, just get in touch and ask. I love talking about this stuff.

With love as always - stay home and be safe.

Ed ❤️🎚🎛

The Science Of Art: Serial Compression

Ahoy - this time we’re talking about serial compression - exactly what’s going on, and why you shouldn’t be too scared of using multiple compressors in series.

Serial compression can be very straightforward: it’s simply 2 or more compressors in series, one after another, with each compressor carrying a little (or a lot) of the workload. It can be used on individual tracks, on the master, or on any busses - in fact it would be rare that any song released these days wasn’t run through a few compressors in series, during mastering.

Essentially, the reason to be aware of/understand serial compression is because you can achieve results with it that you just can't get with a single compressor.

For example, when mixing individual tracks, I’ll often use a fast-reacting compressor with a higher ratio first to catch the higher transient peaks and increase the ‘short-term consistency’ of the audio. Then I’ll follow it up with a slower compressor at a lower ratio to deal with more long-term level variations. This way, the second compressor has a smoother, more balanced signal to work on and won't ‘pump’ or ‘breathe’ due to a sudden burst of energy on signals with occasional loud peaks. I find it really helps with dynamic vocals and inconsistent bass guitar. The classic chain for this kind of thing is an 1176 into an LA2A.

This can often result in a more transparent, natural sounding compression, as well as reduce potential negative artefacts caused by heavy compression, such as treble loss, and/or plugin aliasing - some plugins can sound okay when doing gentle compression but kind of ‘fall apart’ when being pushed. You can also benefit from the colouration or ‘character’ that both compressors will impart on the sound.

However, using two or more compressors means it’s quite easy to over-compress…

Multiplicative Ratios!

Consider a vocal that’s been recorded through a hardware compressor using a 12:1 ratio, followed by two more compressors used in serial during mixing, with a ratio of 8:1 and 2:1. Now let’s say there’s also an SSL bus compressor on the master bus applying a 4:1 ratio (which is a totally reasonable scenario for a mix I might do). What’s the full potential compression ratio that this vocal track goes through?

The answer is…

768:1 (!)

The reason: Compression ratios are multiplicative when over the threshold: 12 x 8 x 2 x 4 = 768

Given that any ratio above 10:1 is considered limiting, 768:1 seems a ‘little extreme’, and that’s before mastering with more compression and limiting. Even with no compressor used during tracking, there’s still potentially a 64:1 compression ratio being applied to the vocal. So yeah… it’s easy to over-compress using serial compression.

To break it down and really help us understand it: imagine two compressors in series, both set at a threshold of -10dB, and both with a ratio of 4:1. Theoretically, this should result in a potential 16:1 ratio using serial compression.

So, if we imagine the audio peaks at -2dB (8dB over the threshold) enters the compressor:

    •    After 4:1 compression the signal is now only 2dB above threshold
    •    Compress again with 4:1 ratio and signal only goes 0.5dB above threshold

So yeah, going from 8dB (initial signal above threshold) to 0.5 gives a 16:1 ratio (because 8 divided by 0.5 is 16).

Real World Usage

But these figures don’t tell the whole story as, in reality, serial compression is rarely (if ever) done by setting the thresholds of the two compressors identically, so the aggregate ratio of compression is much more ‘fluid’. Additionally, both compressors probably wouldn’t have the same attack and release times, the same knee, and so on, so they wouldn’t always be acting on the same part of the signal.

I’ve never even used a Fairchild on a track that ended up getting released, yet here they are, in a picture, on my website.

Some of the signal maybe be uncompressed, some parts compressed by only one compressor, and some by both. Often the second one is releasing while the other is holding, sometimes one can be attacking while the other is attacking or releasing, so the interplay becomes quite complex.

So, the result of two compressors in series and both set to 4:1 - while theoretically identical to one compressor doing 16:1 - is usually an extremely non-linear form of compression, and one that could never be achieved by a single compressor set to 16:1.

Sonically, serial compression tends to be more transparent because the attack of the second compressor is often masked by the simultaneous movement of the first - and because the compression thresholds aren’t the same, the multiplied-ratio compression is performed on a smaller part of the signal than it would be if a single compressor were doing all the work. Read that again and you’ll see that it does make sense!

Obviously, there are no rules – you can place the slower compressor first, letting transients slip though, and then deal with them with a second, faster compressor! I do this all the time when tracking in my own studio, using a DBX 160XT (in over-easy mode) first as an insert, followed by an 1176. Or use two fast compressors, two slow ones, whatever. Take care not to over compress using this technique, just experiment and have fun.

As a parting bonus: you might find that when using serial compression on a vocal requires more de-essing than you’re used to applying. But that’s okay! It doesn’t necessarily mean you’ve ‘over-compressed’ if that’s what sounds good to you, and you want a really upfront sound. Just use the method described here to go in and turn down the sibilant parts - and you might even find that you need to use a de-esser somewhere towards the end of your plugin chain, as well. Don’t worry, if you think it sounds cool, then it’s all good.

With love,

Ed 🎚🎛❤️

The Science of Art: Finding the ‘Perfect’ Compressor Settings – Every Time

Yes, I do realise that it's been a while since I posted, but I've been very busy recording an album. Isn't that nice?

Anyway, when it comes to compression, the truth is that even some experienced engineers and producers can feel frustrated when trying to set a compressor – especially the attack and release times. A technique popularised by Michael Paul Stavrou in his book Mixing with your Mind (a very expensive but highly recommended book!) helps to overcome this.

The method is simple: using extreme threshold and ratio settings makes it easier to hear the effect of changing the attack and release times. The key step is to first apply the following settings to your compressor:

    •    Attack to minimum
    •    Release to minimum
    •    Ratio to maximum
    •    Threshold giving at least 15dB of gain reduction – preferably more

Loop up a piece of audio, such as a snare sample or drum loop you’re familiar with, and start to adjust the attack time until you can hear the transients poking through, and really understand and get a feel for the way that the attack works on the particular compressor you're using. Try to ignore the distortion and extreme compression and just focus on the attack transients; pay attention to when there's too much 'clamping down' on the transient.

Random picture of a compressor I took at KONK Studios

I was going to included a screen capture video of myself, following the process with the built-in Logic X compressor, to show you how quickly it can be done - then I thought, you know what? Nah - you do it. You know? Okay, PERHAPS I recorded it several times, only to realise it wasn’t capturing the screen audio and would be useless to everyone, but let’s pretend that this is a lesson in tough love and DIY ethic.

Anyway, once you have the attack set to your taste, you can move onto the release. Listen for when it’s too fast and there’s too much distortion, or when extreme pumping occurs. Once the release is set move onto the ratio, and finally back the threshold down to give a more reasonable amount of gain reduction, and then set the make-up gain. How does it sound?

This is a great trick to try when you’re using a new compressor for the first time, and want to get to grips with it learning how it sounds and behaves. Be sure to adjust the settings in the following order:

Attack -> Release -> Ratio -> Threshold

According to Stavrou, you shouldn’t ever really need to go back and change the initial settings you chose, unless you decide to go for a completely different aesthetic. It’s a great technique, so give it a try! Bear in mind that different compressors sound… different! Some of them will behave in quirky, non-linear ways that you may or may not like…

You could do all that, of course -  or you could just get me to mix it for you, which will, of course, sound quite wonderful. 😎

Next up, we’ll talk about serial compression - chaining these lovely things together in a row for further awesomeness and sonic beautification.

With love,

Ed 🎚🎛❤️

The Science of Art: Understanding Compression - Part III

OK, we're going to be talking about Side-Chain Compression. It sounds confusing but it's not at all. It's a relatively long post, but just imagine it's the olden days, when people read books and listened to vinyl and stuff. Everyone's obsessed with tape and vintage gear, but nobody wants to read an article full of lovely, free information? Come come now, you know your brain and music will thank you for it later.

Erm, anyway. Grab a coffee. Let's discuss.

Setting up side chain compression in Logic and selecting the kick as the input signal to turn down the bass guitar - but only when the kick hits

7. Side-Chain Input: So, if we're using a standard compressor (as discussed so far) the level of the audio going into the compressor is used to control the amount of compression; the compressor detects the ‘volume’ of the incoming audio, decides if it’s over the threshold or not, reduces the gain of that audio, and then outputs it. OK, easy, we're on the same page.

Side-chain compression works similarly, but the compressor has two inputs: one is the signal to be compressed and the other signal is used to control the amount compression. The "side-chain" of the compressor is the part of the circuitry that listens to the incoming signal to see if it should tell the compressor to... compress.

This can help to create the 'famous ducking effect’ or pumping sound used in electronic music – the kick is used as the side chain input, acting on the bass to ‘duck’ the bass sound (or perhaps all the instruments, if you want) while the kick hits, and then the music comes back in after the kick, helping create rhythm and groove (if the release is set correctly).

This can be used to... ahem, artistic effect as above, or it can be used simply to create more headroom and allow instruments to 'get out of the way of each other' – for example, if the bass and rhythm guitars are playing during a busy section in a mix and masking the kick and the snare, they can be ‘ducked’ a little in order to allow the kick or snare to bang through the mix a little more easily, as well as creating a little more headroom on the master bus (bonus!).

A cool and slightly advanced trick is to 'duck out' the rhythm guitars (or anything playing at the same time as the vocals) so that they dip out when the singer starts to sing. Go wild - you can even try using side-chain compression with a multi-band compressor and only compress the mid-range of the rhythm guitars when the vocals kick in! You only need a few dB for it to be worth it.

Additionally, using the side-chain gives you another important tool - it allows you to filter the input signal separately, before it is fed to the compressor. Using hi-pass and low-pass filters (see attached pic of Logic X compressor) you can compress the input signal, but only when the threshold is exceeded in the range of, for example, 10Hz - 100Hz. This way, when the signal has contains transients outside this frequency range, the compressor doesn't react. Get it?

Obviously, the settings you have on the compressor (Attack, Release, Ratio, Threshold etc.) will affect the character of the 'ducking'. The Release time might be the most important one here, as that will control the 'breathing' effect. Experiment. Stick it on 4:1, set the Threshold to give you -10dB of compression (i.e. enough so that you can hear it) and then experiment with the Attack/Release. You might like the Attack at the fastest setting.

Some compressors have a side-chain listen button that allows you to check which frequencies you're using as side-chain input (see the above GIF). If you push this, you send the side-chain signal straight to the output. Listening to this can really help you understand what the hell is going on.

Here is a picture of some compressors that I took at a session at Real World. It's just here to spice things up a bit, you know? Otherwise it's just a lot of text and people don't wanna read stuff these days. We need distractions. Plus, I think it looks better. Spruces the place up, like a nice throw, some cushions, or a nice lamp.

8. Compressor  Metering - PEAK vs. RMS: OK, so we know that each compressor uses a side-chain circuit to measure the incoming signal, so that it knows when it needs compressing – it asks: ‘is the signal at the threshold, yet?’. But the important part to remember is that the compressor will behave differently, depending on whether the side chain detector responds to the average level of the input signal, or to the max/peak signal level of the input. What?

Well, some compressors can switch between Peak Mode and RMS Mode operations (don't panic, don't close the browser) – in Peak mode, the compressor responds more accurately to brief peaks in the audio - this ensures transients are more accurately controlled, but also introduces a risk that the output will be overly compressed if there’s a sudden loud, sharp transient sound. So Peak metering is usually used on drum and percussion sounds.

Most compressors use an RMS mode. RMS stands for Root Mean Square... which is *clears throat*.... "a mathematical means of determining average signal levels, which is designed to respond similarly to the human ear". Using a compressor in RMS mode means that the compression can sound more natural, but sharp transient sounds may pass through at a higher level than you expect, even with a short attack time. A great tip when working with RMS mode compressors is to use a limiter after the compressor to catch the transients, but be careful not to squash too much of the dynamics!

In the picture at the top (the Logic compressor) the options are 'MAX' and 'SUM' - which is the same as 'Peak' and 'RMS' respectively.

That's all for now. If you need any clarification on anything, just get in touch and ask. I love talking about this stuff. Next time, we'll talk about how to find the ‘perfect’ compressor settings - every time. I don't mean that in a spammy, click-bait way, it's a method I was shown years ago and it's pretty cool.

With love,

Ed 🎚🎛❤️

The Science Of Art: Tip #0001 - Side-chaining

Tip 1.) Side chaining: not just for crazy electro kids with the UNF UNF UNF UNF and the donks. Use it to knock a couple of dBs off your bass line when the kick hits, helping it cut through and keep your master bus from exploding. Used subtly it won’t really be noticeable, and you could even use it so that you can make your track louder overall - but I am hoping that you use these tips for good and not evil.

It doesn't have to be much:

With Love,

Ed 🎛🎚❤️