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Parallel Compression
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And Yet Another Article About Compression?

And Yet Another Article About Compression?

Compression seems like an obsession in the audio world. How many times have you heard “for the vocal I used a bit of corrective equalization, and some compression to taste”, et cetera? It’s everywhere, it’s used and abused and has often played a big part in the sound of a decade. A Fairchild pumping in the 60s, the aggression of an 1176 in the 70s, chip based VCA compression in the 80s, and nowadays digital compression and limiting (yet another subject). This explains why there are countless articles and videos about compression in the first place, often very well detailed and insightful. And it’s also why I want to do something slightly different with this article. You can study compression as much as you want, but you also need to master it through real life application. That’s what I’m going to talk to you about here, by displaying a few real life examples.

Longer release times, Why?

When you’re starting out with compression, you might be tempted to overuse it (especially with plug-ins). Or tempted to only use slower attack and faster release times. How often have you already heard or seen this combo somewhere? Slow attack and fast release? It seemed to me, when I first started, to be the magic combo for compression. I used it almost all the time. The results? Everything was enhanced to have punchier transients, and therefore nothing really stood out of the mix. This is a big reason why longer release times can be useful. Even if not by purpose, you’d be surprised how often you’re using slower release times without realizing it. An LA-2A for example is entirely program dependent. But its release time can reach five second for full release! That is super slow, and can happen when you are really pushing the compressor while processing steady bass notes, for example (constant 1/8 notes). I find myself reaching for slower release times during a number of scenarios :

  • To tame a harsh sound, or overly trebly instrument. Yes, slow release can do that (often combined with quicker attack times). And I love using clean compression for this to really shape the sound without any unwanted color (compared to very colorful, darker compressors). Hear for yourself: 

TAMING HARSH SOUND OFF

TAMING HARSH SOUND ON

TAMING HARSH SOUND EVEN MORE ON (darker compressor)

Can you hear the difference in the high end? Subtle, but pretty sweet, right? This could partly be explained by the Fourier Theorem. It also comes down to the fact that high frequency waves have higher energy (faster moving, shorter waves) in comparison to lower frequencies. They will quickly hit a peak while lower frequencies would still be on the upslope (this is also linked to the aperture size). So if you combine quicker attack times and slower release times, you will reduce the peaks and be able to rebalance the high frequency peaks to a similar level as the lower frequency information.

  • To even out complex material and create a sense of “unity”. Often combined with slower attack times, the impact is much more obvious on the mix bus. Hear for yourself :

Slow A. Fast R.

Again, the difference is subtle but you can hear how the slow attack/fast release created a different movement that, in my opinion, is adding forwardness to the sound but less sense of “glue”. It makes the song a bit more “awkward” and uncontrolled. Whereas slow attack/release gave a greater sense of cohesion, while at the same time reducing a bit of overall reverb and being less “impactful” than slower attack/faster release times.

Not every song has to be punchy and forward. Sometimes you want it to be soft, easy-going and “united”. Using the classic slow attack/fast release will go against that feeling and will do you a small disservice.

The strategy behind faster attack times.

As we already heard, fast attack times will reduce the peaks. But there is a further strategy behind using faster attack times. It is a lot more than just taming peaks. Faster attack times combined with faster release times can help bring out the sustain of a sound, as you can hear :

FAST ATTACK OFF

MORE SUSTAIN ON

But there is also something else I want to mention. Not every fast attack setting is equal, as you can also hear:

FAST ATTACK OFF

FAST ATTACK A

FAST ATTACK B

FAST ATTACK C

When using analog compression (emulation or real hardware), fast attack times can sometimes enhance the very first peak(s) as the compressor is often too slow to catch the first milliseconds of an input (that is where look-ahead features come into play). Combine this with the different levels of THD each compressor may contribute (faster times generally increase THD), and you will yield totally different results from one compressor to the next. Because of this it’s important to grab the right compressor for a specific task. In a mixing scenario, combining faster attack times with an instrument that has a slow attack time (and a cleaner compressor) can completely re-balance everything and change the focus and energy of a song. Here is a very basic example:

REB. BASS SLOW Attack

REB. BASS FAST ATTACK

You can hear the bass distorting a bit more with faster attack times. And you can also hear how different both examples are and how one can feel a lot better than the other. This is by simply altering the attack/release times of the compressors on both audio tracks.

The trap behind parallel compression

Aaaah parallel compression… that big thing, the “secret to pro mixes” as it is advertised by seemingly everyone. But like all good things, there must be some shortcomings to it.

Parallel compression is a smart way to make a sound more intense, dense, and/or snappy:

FAST ATTACK OFF

PARALLEL COMP SNAP

PARLLEL COMP SUSTAIN

You can increase either the sustain or the initial attack of a sound as shown above. Although, parallel compression can also be a source of confusion.

FAST ATTACK OFF

PARALLEL COMP CONFUSION ON

Seems better when it is on right ? Well not really, it is just louder. Let’s do the same comparison, but this time, instead of muting the aux where the parallel compressor is, we are going to mute the insert on that aux.

FAST ATTACK OFF

PARALLEL COMP CONFUSION ON

PARALLEL COMP CONFUSION OFF

The benefits are much less evident now, right? It almost brings more of the mic bleed than any real noticeable benefits. In this example, to my ears it sounds like a +50% bleed increase for a +10% overall enhancement. Which means that the compressor/attack/release settings aren’t right for the source. Especially since I showed you everything in solo. In the context of a mix, it can create a sense of confusion, and no real practical improvement… imagine this on your whole drum bus! Bringing up all that cymbal bleed while barely helping the kick and snare cut through.

This is the hidden trap behind parallel compression! You can easily get fooled by the volume increase, which is the case when auditioning anything at differing volumes. And level matching with a dry/wet knob can be quite complicated at times. So it becomes hard to judge if a decision really benefits the mix or not. My advice: if you use parallel compression on an aux, always A/B by bypassing the insert (plugin or hardware) instead of the whole aux track. To ensure that levels are matched more precisely.

CONCLUSION

To wrap things up, I will share a bit of my personal opinion on compression. But first, to sum up this article, I would say that compression is something that can drastically change a sound (#captainobvious) and the balance of a mix.

It is not something to use in a casual or uninformed way, it needs to have a purpose and satisfy a vision… in my humble opinion. Because compression can also have impacts that may be undesirable. This is when parallel compression can become especially useful. But, as we saw earlier, this can also act as an additional source of confusion. So how to use compression properly? When? Which compressor and attack/release times to choose? Which ratio? Knee? Well, I hope this article is helpful to you in finding an answer to these questions, or at least gets you started in the right direction. Being able to answer all of this, in every situation, takes time! Yes, I am sorry to say it: time, experience, trial and error, discussion, etc. There are no shortcuts to knowledge and no shortcut to technical abilities and awareness on how/when to use that knowledge in a real-life scenario.

Now my opinion about compression. When I first began, it was a love/hate/fear relationship. At first I thought “woooow punchy, louder, saturaaaation”. And then I realized that plugins induce artifacts (aliasing, weird behaviors etc.) in addition to the compression’s artifacts. So I went the opposite “Al Schmitt way”: Using as little compression as possible to keep the integrity of the source. But this resulted in my mixes often sounding a bit dead and not exciting enough. Like a nice demo. So where am I now? Currently, when it comes to compression, “it depends” (the classic audio engineer answer haha). If you are mixing a song that is supposed to sound natural, lively, and “organic” (folk music, songs without a lot of percussion or percussive elements, etc), I urge you to start working with volume automation instead of compression. If you can balance the whole mix with just automation instead of EQ or compression, then that is pretty amazing and speaks volumes about the recording as well! And yes, even on the vocal! Compressing a vocal seems to almost be an auto-pilot thing nowadays. But it does not always need to be compressed, especially if your automation work is bold and precise.

You just received a song with 135 tracks of different plucky synths, funk guitars, vocal harmonies, percussion instruments, etc… if you don’t want to use compression it is going to be a lot harder and longer to make everything work together. You will need to compress elements so they all don’t stand out in the mix and fight with the main elements of the song (lead, kick, and snare for example). And that is also when you can revisit this article to remind yourself of some ways to balance the mix with different compression times, and of the other techniques we touched on. So don’t be afraid of compression, but please, for the love of music, don’t do it on auto-pilot. Always question what you read (this article to start with!), what you see, and what you hear. Be curious about everything you can if you want to seriously pursue this craft. There are plenty of engineers/producers. But you can still stand out of the crowd if you are not afraid to learn, to try, and to avoid lazy shortcuts in order to have a precise thought behind everything you do. Have fun mixing and tweaking!

Written By Wheeliemix

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3 thoughts on “And Yet Another Article About Compression?”

  1. Could you explain a bit more about bypassing the input to the parallel compressor please, (I don’t understand what this does differently to muting the aux track). Thanks for this article it was informative, though most of the audio examples were grayed out and couldn’t be played . Regards, Chris

    1. The idea behind bypassing the plugin is that you still get sound through the Aux track so you still make the audio louder in the mix but without enhancing it with the compressor. Basically because the audio gets doubled. On the other hand if you mute the Aux track itself the audio doesn’t get louder in any way.

    2. Hey Chris, just now seeing your post. Like what Carlos said, basically what the article is describing is a method to make sure that your opinion is not being swayed just because the track is louder. Psychologically we tend to prefer louder tracks just because they are louder, even if something is having a negative impact on the track. I have seen some beginner mastering engineers fall for this, and send over a master that actually trashes the mix in some way (distortion, overly crushed with limiting, lower bit depth, etc), but both them and the artist thumb it up at first because that increased loudness is hard to hear past subjectively. So in the case of this article, you are keeping the aux track about as loud both with and without compression while you audition the parallel processing with this technique. This gives you a fair comparison of processed vs not processed.

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