Bus Compression 3

Back in October last year I wrote a post about bus compression, and what at that time was my default effects chain for master bus compression. Some time’s passed since then, and my standard master bus effects chain has evolved further, and using this chain and new techniques I’m now able get pretty significant level increases (5-6dB) whilst still maintaining a reasonable transparency and general mix clarity.

New Plugin

The biggest change to the setup is the final limiter plugin. Previously I was using Waves L1 for this, and whilst it’s a useful tool, and definitely very good for transparent limiting on individual sounds, it’s also getting pretty old (not sure exactly when it was released, but it was more than 12 years ago), and I find that across a whole mix, it tends to add artefact, and lose some transparency when more than around 3-4dB of gain reduction is applied. After looking at a couple of different options as a replacement, I bought the T-RackS Stealth Limiter after reading a couple of favourable reviews. I have absolutely no regrets about this… the amount of gain reduction it can provide without any adverse artefact is quite amazing (this was one of the reviews that convinced me incase you’re interested).

Effect Chain

I’ll go through the exact effect chain and settings I used on Cantana 2. In the previous post I discussed using Waves L1 as the first step in the chain, to even out transients and allow subsequent compressors to work more easily… and this aspect hasn’t changed. In Cantana 2, I used threshold of -3.5dB, with the fastest release setting, just to catch and even out the really fast peaks…

bus-compression-3-1

Another significant change is that I now tend to use two instances of Cytomic’s ‘The Glue’ in series. The main difference between these two instances is in the attack and release settings… the first tends to use quicker settings in order to further (but more gently) even out peaks, whereas the second uses slower attack and release to provide a smoother, more general gain reduction.

For the last couple of tracks, I’ve used parallel compression in the first Glue instance… using a high ratio and low threshold to really squash the sound, and then using the dry/wet control to blend it back with the original signal. The settings used for Cantana 2 are shown below…

bus-compression-3-2
Threshold: -17.8dB
Makeup: 3.8dB
Mix: 12%

One thing I’ve found with parallel compressing in this way, is that it’s easy to either compress the wet signal too much, or blend too much of it back, and adversely change the level balance of different instruments in the mix. I had this problem with Cantana 2 initially, where the snare/clap sound in the original mix was still quite dynamic and peaky… this meant that the low threshold / high ratio settings tending to really squash the snare and introduce ‘unmusical’ pumping. When blended back with the original signal, the net effect was that the level of the snare dropped in the mix (sounded very similar to dropping the snare level by 1-2dB in the original). I fixed this by going back to the original mix project, and adding a bit more compression to just the snare track… this reduced the peakiness, and allowed The Glue to compress the whole mix more smoothly. Still I was surprised that the difference between what I considered the ‘right’ setting for the threshold, and having too much compression was only roughly a couple of dB, as the two clips below show (in these, the first Glue instance is set 100% wet for demonstration… 12% of this was mixed  back with the original signal in the final settings)…

Threshold: -17.8dB

Threshold: -19.8dB, Makeup gain increased to level-match. Notice the drop in level/clarity of the clap/snare, and pumping effect on the piano part.

The second instance of The Glue used a lower ratio, and slower attack and release (release set to the ‘Auto’ setting). This created a kind-of ‘continual’, general compression over the mix, to give a couple of extra dB of gain reduction…

bus-compression-3-3
Threshold: -14.2dB
Makeup: 3.2dB

One interesting comparison between the instances of The Glue, was the movement of the virtual ‘compression’ needle in the UI. The needle in the first tended to move quite quickly in response to the dynamics and rhythm of the track, whereas the second tended to stay around the 3-4dB mark with little movement. Before buying The Glue I hadn’t used a hardware compressor (nor plugin) which had a needle to show the amount of gain reduction… but I’ve found it’s a really useful supplement to know what the compressor is doing, and understand whether it’s imparting the effect you want.

The final link in the chain is the T-RackS Stealth Limiter, and for Cantana 2, I used the following settings…

bus-compression-3-4

This was quite a lot of limiting, and to be honest more than I would like to use, but necessary to be competitive with other tracks in the same style. The nice thing was that the progressive application of compression through the whole effect chain meant that I could use such aggressive settings in the Stealth Limiter whilst still maintaining reasonable clarity and transparency.

I find that applying compression like this to the master bus can sometimes cause a loss of high end, and in the case of Cantana 2 I used an EQ with a very slight high shelf boost to compensate for this (placed before the Stealth Limiter)…

bus-compression-3-5

Anticipating the Effects of Compression

I touched on this briefly in my last post… obviously introducing compression (and especially significant amounts of compression) is going to alter the level balance of different elements in a track… and I’ve found it can be beneficial to anticipate these changes and compensate for them in your original mix accordingly. The case I discussed in the last post related to reverb… reducing the dynamic range of the sound brings the level of quieter parts (like reverb effects) closer to the main sounds in a track, so in Cantana 2 I dropped the level of the overall reverb sends by a couple of dB in the original mix, and then re-rendered it for bus compression. I did a similar thing for some of the low-level background/atmospheric incidental and percussive sounds in the track too… without dropping the level to compensate for the compression, the final compressed mix turned out a bit ‘muddier’ than the original. Another useful tip is to render small, key parts of the original track (rather than the entire track) when auditioning these level changes. I’m using a fairly old PC, so the mix project (with stacks of plugins and including multiple CPU-intensive reverbs) only renders in slightly better than realtime… it’s much more efficient to try dropping the levels of the quiet parts by a certain amount, and then just rendering short clips of the key sections of the track. These short clips can then be imported into the bus compression project, and the changes auditioned without having to wait for the entire track to render.

Results

The net result of this new approach is I’m able get more competitive levels, and still maintain a more clean/transparent mix than before. It again reiterates my belief in a progressive/layered approach to compression that I discussed in my first bus compression post. The less work a compressor has to do, the more easily and transparently it can do it, so using multiple, staged applications of compression for different specific purposes seems to make sense. Following this idea over the last 12 months has also made me have a greater consciousness of compression and evenness of levels during the writing and mixing phases of a track… so my mixdowns prior to bus compression tend to have a lot smoother and more even levels to begin with. You can see this by just visually comparing the pre-bus compression render of an earlier track (The Yellow Room) against Cantana 2…

bus-compression-3-6
‘The Yellow Room’ pre-bus compression waveform
bus-compression-3-7
‘Cantana 2’ pre-bus compression waveform

If you’re writing in a style where competitive levels are important, the more you even out the levels in the early stages of writing and mixing, and the more progressive approach you take to master bus compression, the more easily your final limiter will be able to get to the required competitive level.

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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.