Adjusting Effect Levels for Mix/Bus Compression

I spent a few hours yesterday doing final bus compression for the track I’m currently working on. Approaches to and techniques for bus compression were one of the things I learnt most about during 2016, and yesterday I had a kind-of ‘lightbulb’ moment, which will hopefully lead to better results in this area going forward.

I’m a ‘reluctant participant’ in the whole competitive levels/loudness wars thing. Fundamentally I like the groove, emotion, impact, etc which a decent dynamic range can impart on a track. But at the same time I understand the need to achieve an overall loudness level that’s similar to other tracks in the same genre (especially because not doing so simply makes your music difficult for DJs to mix).

In the past, I’d always equated greater amounts of bus compression to a loss in clarity. To some extent this is true, as compression will narrow the dynamic range of the sound and hence simply reduce the ‘depth’ of volume variation available. However I’d always found that compressing the entire mix necessitated a compromise of getting closer to competitive levels while sacrificing some detail and clarity.

About halfway through last year I had a mini breakthrough of sorts, when I realised certain settings on bus compressor plugins can have a big effect on the quality of the resulting audio. Specifically I usually use Cytomic’s ‘The Glue’ as the first stage in the bus compression chain, and I found that simply setting the oversampling rate to the recommended or higher levels (4x or more when auditioning) gave far clearer audio quality than the default lower settings.

For my current track I had spent a bit longer than usual honing the reverb plugin settings, and fine tuning the reverb send levels. After this I was really happy with the result… it had a nice balance of having a good depth/space with sounding too ‘washed out’, and seemed to translate well to several different sets of speakers and headphones. But yesterday it was a bit disappointing to have some of this clarity and balance lost when I started pushing the final mix through bus compression. When I listened closely it wasn’t so much a by-product of compression, but more that the levels of the reverbs and delay effects were stronger. When I thought about it, the reasoning was obvious… I’d squashed down the top 3-6 dB of the volume range, so obviously sounds down at -15 to -20dB (like the reverb layer) had been effectively pushed up by a similar amount.

I usually do final bus compression in a separate Reaper project to the mixing, using just the final stereo mixdown as a source track (my aging PC can’t handle multiple reverb plugins and CPU hungry bus compression at the same time). So I went back to the mix project and rendered another version of the stereo mix with reverbs and main delays turned down around 1.5dB. Running this new version through the same compression chain resulted in a much clearer mix… it sounded a lot more like the former original stereo mixdown… just louder (which is exactly what I was trying to achieve).

Anyway, in hindsight I’m a bit surprised it’s taken me this long to figure out this technique (the basic point of compression after all is to reduce dynamic range), but I’m going to experiment a bit more, and hopefully end up with a lot cleaner, clearer final mix than for past tracks.

Another way to potentially prevent the issue could be to ‘mix into’ a compressor or limiter during writing/sequencing/mixing. This is a bit unorthodox technique historically, but seems to have gained popularity in the last few years (I seem to have read a lot of articles recently where people discuss working this way). The idea is to put a limiter/compressor on the master bus right from the early stages of writing (using generic/default settings close to what you’d usually use for final bus compression). This way you’re always evaluating level balance with compression already ‘baked in’. I don’t usually use this technique because for some reason I like to keep a clear separation between the mixing and final ‘mastering’ stages… but based on yesterday’s experience I can definitely see the merits, so may try it in a future track.

Mix Issues – Prevention Rather than Cure

Thanks to the rapid development of DAWs and plug-ins over the last 5-10 years, as producers we have close to unlimited flexibility in terms of audio processing.  Even my very old (7+ years) music PC is capable of running 10’s to 100’s of simultaneous plugins in a track’s project.  Added to this, the internal digital routing in a DAW, and the ever-increasing quality of plugins, means chains of 10’s of plugins are not only a reality but often the norm in putting together a track.

But with this flexibility can come a complacence to ‘fix problems later’ with plugins, rather than dealing with them at the source.  I’ve read numerous interviews with pro producers who emphasise the importance of getting sound right in the first instance… particularly with things like tracking… finding good sound through good mic selection and placement, rather than fixing it with EQ in the mix.  Yet, it can be easy to forget or ignore this advice given how simple it is to throw extra plugins in an effect chain.

While writing ‘Dystopia‘, I came into this kind of situation… a problem which could have been fixed by additional tweaking, or extra layers of compression… but which actually had a simple, and probably ultimately better sounding solution at the source.

The track has the following background percussion pattern in various sections…

Within an 8 beat phrase, the first percussion ‘hit’ occurs on the third 16th beat, and has a quieter and lower pitched ‘grace note’ a 16th before that.  The below screen shot shows the MIDI sequence for the pattern, with the grace notes highlighted…


At the point of final mixdown and applying bus compression, I noticed that there were occasional waveform spikes at the points of these grace notes… the highlighted peaks on the below waveform show an example…


These spikes were not only quite strong (almost hitting 0dB), but occurred on a rhythmically odd (syncopated) beat of the bar… i.e. the second 8th beat of the bar… at the same point as the offbeat hi-hat sound.  When I was trying to apply compression, the strength and syncopation of these spikes were causing the same type of uneven, pumping compression I mentioned in my second bus compression article.  The problem could have been cured at the final mix stage by potentially applying a limiter or a fast acting compressor at the start of the effect chain.  But instead, I went back to the MIDI sequencing and took at look at the part itself.  Considering the note at the second 8th beat was just a grace note, and that it occurred on the same beat as a rhythmically far more important part (i.e. the offbeat hi-hat), the MIDI velocity of that note seemed quite high (at around 81).  Hence, I tried simply reducing the velocity of the grace note to about 70 as per the below screen shot…


…and this simple change benefited the mix in 3 ways…

  • It left more room for the offbeat hi-hat, and hence made the hi-hat clearer.
  • It wasn’t in any way detrimental to the in-context sound of the percussion part (actually, I think it sounded better after the change).
  • It had the effect of removing those waveform peaks, and hence let the compressor work more smoothly and musically (see the ‘after’ waveform below)…


Ultimately, a simple changing of MIDI velocity fixed the problem, and was far easier to implement than extra layers of limiting and compression would have been (and also avoided the additional side-effects that limiting and compression could have introduced).

Clips of the ‘before’ and ‘after’ full mix are below…



The interesting take-home from this experience, was to always think a bit ‘out of the box’ with regard to mix problems… to consider whether there’s a simple preventative measure that could avoid or correct the problem in the first instance.  In 99% of cases, as the pro producers advise, such a prevention is probably going to be easier and more effective than the equivalent cure.

Bus Compression 2

my experience in this process was one which helped me discover, and then cement the approach of progressive compression

This is my second instalment on bus compression, and the story of how I discovered what has since become my default effects chain for master bus compression.

I discussed in my last post on this topic the importance of applying compression in a staged and progressive manner through the entire sequencing and mixing process, rather than leaving all the work to a couple of plugins at the point of final ‘mastering’.  My experience in this process was one which helped me discover, and then cement this approach of progressive compression.

It centered around my track ‘Push On‘… when I’d completed mixing of this track, I was really happy with the sound… the bass line was strong and solid, and the snare and synth ‘stab’ sounds both had a nice punchy and aggressive dynamic.  What I basically wanted to achieve with bus compression was to maintain the general sound and dynamic as much as possible, while making the overall level more ‘competitive’.

My ‘goto’ compressor for bus compression is Cytomic’s ‘The Glue’, so first step was to insert an instance of this over the master mix.  Initially I used a slowish attack setting of 0.3ms, but I was finding a lot of transients were slipping through and causing digital clipping when the level was raised.  If I moved the attack back to 0.01ms, it caught all the transients, but also resulted in a fairly un-musical pumping effect.  The clips below contain 1. the track directly after mixing, and 2. the same track plus ‘The Glue’ with similar fast attack settings to what I used originally used…

Original track:

The Glue with fast attack:

The pumping of the compressor is evident from the uneven level of the offbeat open hi-hats.  While originally working on this I also noticed that the virtual ‘needle’ in The Glue jumped around unevenly, not moving with the rhythm of the track.  (From further experience since this,  I’ve come to learn that un-rhythmic movement of the gain reduction needle like this usually always results in uneven, pumping compression).

I bounced the uncompressed track to an audio file so I could get a look at the waveform (see below)…


Notice the highlighted uneven peaks caused by the synth stab sounds (red) and snare hits (blue).  The synth stab used a fairly heavy chorus effect which caused the individual notes to peak at varying levels in the waveform.  My assumption was that at fast attack settings, the uneven peaks of both instruments were causing the compressor to trigger inconsistent amounts of gain reduction.  Coupled with the fact they were on syncopated beats of the bar (especially the synth stab which was on the 3rd 8th note), this was likely what was causing the un-rhythmic pumping of the compressor.

I used a combination of techniques to ultimately correct this, but the one which had the biggest impact was to put a limiter (Waves L1) in the signal chain before the compressor. This had the effect of evening out the transient peaks, and allowing the compressor to operate much more consistently, aswell as permitting the use of a slower compressor attack setting.  This resulted in a much more transparent compression.  The clip below demonstrates a recreation of the same signal chain…

…notice that the sound generally is much smoother, and the consistent levels of the hi hats in the original version have been maintained.

The end result was a considerable amount of compression was applied by The Glue, but it remained relatively transparent.  The final step was to use another instance of the L1 limiter at the end of the chain to bring the track up to competitive levels.  The final chain and settings were as follows…




I mentioned that ultimately I used several techniques in addition to the above signal chain to achieve the result in the published version, and this included actually going back to the mix project, and applying more compression, and some limiting to the individual snare and synth stab tracks in that project (supporting my earlier comments about a ‘progressive approach’ to compression).  That meant that the first L1 instance in the master bus chain had even less work to do, and again produced an overall more transparent result.

The whole process was a really good learning experience, and the L1 > Glue > L1 effect chain has become my default for master bus compression.  If you struggle to get clean but loud results with your own master bus processing,  I hope sharing my experiences will be useful.