The Science Of Art: Parallel Compression

Following on from the last post on Serial Compression (back in 1872), I thought it would be good to post a guide on Parallel Compression. I was actually writing a post on mix bus (aka master bus) compression and thought it’d be a good idea to include this topic first as I might refer to it a bit in the next post. Click here for a handy overview of all 5 previous parts of the series on compression.

Random picture of some DBX compressors @ KONK Studios (London) so that you don’t glaze over from looking at all this text

Let’s get right into it: parallel compression is when you blend a compressed version of a track with the original track. That’s literally all there is to it, don’t let anybody scare you into thinking it’s more difficult or complex than that.

It’s sometimes called ‘New York style’ compression by people who want to make it seem like they are more elite than you and have top secret references and knowledge that you simply don’t understand.

It allows you to use to extreme compression settings without completely destroying the transients (aka the peaky out-y bits) of your source audio - that’s why it’s often used on drums, you can use it to bring out the room sound of the drums and the sustain of the cymbals - without absolutely trashing those spiky transients, which help give the ‘punch’. But you can use it on any source you’d like, of course (including the mix bus…). Simple, but cool.

Wet/Dry Blend Knob

Nowadays, most plugins have a mix knob or a way to blend the dry/wet levels (dry being the uncompressed or unaffected signal, and wet being the compressed signal), so you can achieve parallel compression just by tweaking this mix knob - you’re probably already doing it.

If you’re using a hardware compressor alongside your computer, you can use an I/O insert plugin to insert the compressor/FX, then there’s usually a mix slider on the plugin. Just be sure to hit the ‘ping’ button (other DAWs will have something similar), which will compensate for the latency introduced by the round trip out of your sound card and back.

There are a couple of other ways to achieve parallels compression that gives you a lot more flexibility: by ‘multing', and using sends.

Multing

Another way to achieve the same effect is to simply copy your track, compress the crap out of it, turn it down, then bring it up to blend it with the unaffected track. This is also sometimes called ‘multing' - e.g. splitting a guitar into compressed and uncompressed by multing the same guitar recording and sending one to a compressor blending the two sounds. And you don’t need to only use compression, you can EQ it, add FX etc, then blend it in with the original track.

Some people even ‘mult’ a vocal and split it into three using EQ - low end, mids and highs, treating them all differently and blending them all back together - but those people are usually mad.

This technique is cool as you can automate and add a bunch of EQ and other effects to the ‘multed’ track.

Send It / Go Full Send / Other Word Play

You can also use a ‘send’ to send the audio to a bus, and then compress that bus - you’ve probably already done this with reverb. For example, you could make a ‘smash bus’, that you send the kick and snare to, and blend that in a tiny bit with your original kick and snare. Or just the drum room mics for a section of the song. You can even gate the input, if you want. Go wild, it’s your party.

It’s a reference to Lost In Space, incase you were wondering

DANGER WILL ROBINSON

One thing to watch out for when using the last two methods: don’t get tricked into thinking it sounds better just because you’re added more ‘stuff’ to the original signal. Obviously if you take the original sound, duplicate it, compress the crap out of it and then blend it in with the original, it will sound louder because more is more. But you’re too smart to fall for that, I believe in you.

Adding a low or high pass filter can make a huge difference to the sound of the compressed track and can enable you to go way more extreme with the compression (or distortion, at this point). Remember that you can EQ the signal going into the parallel compressor, OR after the parallel compressor. Try chopping a load of low end off before it hits the compressor and compress really hard, then blend back in with the original…

Don’t feel the need to use loads of the compressed/crushed signal.

Finally, if you’re trying to use a tape machine or tape machine plugin to get tape compression, parallel compression might not work due to wow and flutter (when using a plugin, you might be able to turn this off) - but it will probably sound like a cool phase/flanger effect!

When Do I Really Use It Though

I tend to use it more with extreme distortion levels of compression (or just distortion/saturation full stop) or when the compressor or effect adds a bit of ‘colour’ - but I don’t want too much. I automate the effect in/out of sections a LOT.

In terms of pure compression, I use it when I ‘kinda like’ what the compressor is doing but know that deep down it’s detracting from the original source. So I’ll try to turn down the mix knob and see if I can have the best of both worlds.

Try It Backwards

Something I often try towards the end of a mix: if things are sounding a bit ‘squashed’ or I want more of e.g. a drum element, I’ll send some of the ‘dry’ drum - e.g. a kick and snare direct track - directly to a the master bus, bypassing the drum bus compressor. Because it’s hitting the mix bus and bypassing the drum bus compression and effects, it gives a completely different sound that can be really cool.

If you think about it, it’s a bit like the inverse of parallel compression - I’m adding more of the original signal on top of the compressed version. You can do this e.g. for just the choruses when everything kicks off once the guitars kick in and the snare gets a bit lost - you might need the snare to poke out more when the mix bus compressor is clamping down on the whole mix. You could automate up the ‘extra’ snare just on the chorus for a bit of extra impact.

Alright, this is getting a bit complicated now.

So anyway: parallel compression is when you blend a bit a compressed signal with the original signal and that’s it, go experiment and have fun with it.

Next up, mix bus compression.

With love,

Ed ❤️🎚🎛

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: 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: Understanding Compression - Part II

Continuing from Part I where we discussed the Threshold, Ratio, Attack, and Release, this post is mainly about the Knee. It's a bit of a weird one, really - it's not a setting on all compressors and people can get it confused with its relationship to the Attack time. We'll also look at Make Up Gain. To start, here is a nice picture of a compressor:

I changed the picture to the white SSL clone compressor in Logic X and made it into an animated gif because I was worried that simply posting factual information would be too bland for the general public to consume. Needed to make it more flash to attract the moths. The barracudas.

So what the hell is the Knee and how can it be 'hard' or soft'?? Let's discuss:

5. Knee: This is how quickly the compressor ramps up to the full compression ratio.

With a hard-knee compressor, the signal is completely unaffected until it goes over the Threshold; from the Threshold on up, the signal is compressed according to the Ratio, and the full amount of gain reduction is applied as fast as the Attack time will let it.

A soft-knee means that the compressor will slowly ramp up the compression Ratio as the signal approaches the Threshold. Another way to think of it is that the Threshold is ‘spread out’ over a wide range and it gradually compresses more and more as the signal gets ‘hotter’. With a soft-knee compressor, once the signal passes the Threshold, the full Ratio that you set is applied, but because some compression is applied to signal as it's approaching the Threshold, the transition from no gain reduction to full gain reduction is smoother. The result is more transparent, less obvious compression (so, it can also seem harder to tell when the compressor is engaged and when it isn’t).

Check out the animation up on the right. This picture shows the settings on a compressor - the vertical axis represents the volume in dB - the horizontal axis represents the Threshold. On the horizontal axis, you can see that the threshold is set to around -21dB (so the compressor will kick in once the signal goes over -21dB). In one picture, there's a sharp fall off in gain, but on the other, there's a gentle curve, more of a transition. All that's happening here is that I'm changing the knee from hard (sharp transition), to soft knee, so there's a more gradual ramping up of the compression. You can see that in the 'soft knee' example, the curve actually starts before the threshold of 21dB, so you'll get some compression happening before -21dB on the meters! However, I didn't touch the Threshold setting when making this picture.

Some compressors give you the option of varying the Knee setting, and some don’t – in any case, experiment with what sounds good to your ears!

I find that a soft knee is nice on 'slower' instruments, so some bass, vocals, piano. Hard knee is great for things like drums or more percussive guitar, rap vox etc. But there are no results - I've used soft knee on drums and hard knee settings on vocals all the time. just mess with it a bit, see if you can hear a difference, and leave it where you think it sounds best. That's it.

A compressor I absolutely love is the DBX 160XT - this compressor doesn't give you any Attack and Release controls (partly why I love it - two less things to think about) but it DOES give you a 'hard knee' (the default) and a 'soft knee' setting (called 'Overeasy' mode) to give you a little control over how 'aggressive' the compression is. But does that mean that the a soft knee is the same as a slower attack? NAH MATE.

So how is the Knee different from the Attack Time?

Remember - the Knee has nothing to do with Attack or compressor timing (if the compressor’s Attack is set to 20ms, it will always be 20ms), the Knee has to do with varying the compression Ratio before the Threshold.

To illustrate, think of a compressor set with a 4:1 ratio, using a soft knee, with a threshold set to -10dB. So, when the signal reaches a level of -10dB, the compressor will be operating at a ratio of 4:1. But before the signal gets to -10dB, the Ratio will slowly increase. So, the compressor may behave something like this:

    •    When the audio signal's at -14dB, the compression ratio is 2:1
    •    When the audio signal's at -12dB, the compression ratio is 3:1
    •    When the audio signal's at -10dB or higher, the compression ratio is 4:1

At -10dB or higher, the full compression Ratio is applied. Of course, in reality, the Ratio wouldn’t jump up in such large amounts, but would be a gradual ramping up to 4:1.

If a hard-knee compressor were being used, there simply wouldn’t be any compression occurring at all until the audio had gone over the Threshold. With the soft-knee enabled, the compressor starts compressing as the signal approaches the Threshold.

So whatever the Knee setting or the current compression Ratio, the compression is still applied after how however long the attack time is set to!

Next up - once you've compressed the signal, it's really quiet. How do you get it back up to the volume it was at? Simple...

6. Make Up Gain: This is used to ‘make up’ the volume of the audio after the peaks have been compressed. Be careful not to be fooled by volume – we always think louder is better. Make sure to always check the real difference that the compression makes by setting the make-up gain so that the peak volume of the audio stays the same when you bypass the compressor. Bypass the compressor and switch back and forth between the compressed and uncompressed audio and listen for the difference, and decide which you prefer. You might be surprised that you prefer the original signal!

Q: If I’m getting 8dB of Gain Reduction and I use 8dB of makeup gain, why doesn’t the output level always match the input level – why is the output louder?

If you’re compressing a signal with sharp transients, and attack time is greater than 0ms, you’re letting the peak transients through and then adding the compressed tail and make up gain on top of that! You can’t always simply add 8dB of make up gain if you’re getting 8dB of gain reduction. Just use your ears, and check the meters too.

If you have any questions at all about any of this, or want to inquire about me mixing/mastering some of your music - just shoot me a email! We can even do a Skype/FaceTime Lesson to talk about this stuff if you like, it's all good fun.

OK, until next time, where we'll look at Side-Chaining and Peak/RMS metering...

With love,

Ed 🎚🎛❤️