Mixing with 2-bus processing

Mixing with 2-bus processing – for

As you already mentioned, mixing with bus processing allows you to work towards your “final sound” in one go. This is particularly useful when 2-bus processing is used for more than mastering (preparing a mix for a distribution format/medium). The best-known example is pumping compression. It’s not so easy to put together a mix where pumping 2-bus compression is a feature element if you’re not actually hearing it when you’re mixing! 

On the more extreme end, other processing tools are appropriate for inserting on the 2-bus while mixing. Personally, I’ve used things like buffer stutter effects, stereo width manipulation, filters, and even distortion. Mind you, these (even the stereo width manipulation) were not for mastering – they were “effects”. They were usually automated, and only enabled for specific sections of a song. 

On the more subtle end, I’ve heard of mix engineers “mixing into” a 2-bus compressor. Not necessarily to get an obvious “pumping” effect, but to gel the mix together. Apparently doing this allows the mixer to get away with using less channel compression. 


Mixing with 2-bus processing – against

One of the important reason not to mix into a 2-bus compressor is that it can be easy to start chasing your tail in circles. It can make mixing difficult because adjusting one instrument can radically change the behaviour of the other instruments. In the simplest case, turning an instrument up will subsequently cause other instruments to drop in level when that instrument in playing. If you’re not watching for it, you might later try to turn those other instruments up and wonder why the rest of the mix is dramatically rearranging itself with your every move. It can also make it difficult to compensate for (or keep) complex relationships between instruments. 

Another trap is using 2-bus processing to compensate for mix problems, when a more appropriate tool would be processing on individual channels. The obvious example is EQ. If there’s not enough bass (for example) in your mix, you might adjust the EQ on the 2-bus as a shortcut to adjusting the kick and bassline individually. By taking the shortcut, you’re adjusting the frequency spectrum of the kick and bassline in the same way, by the same amount (when it might be better to make more tailored adjustments). You’d also be boosting the bass of every other instrument in the mix. Unintended consequences may apprear later, and you’ll be scratching your head. 

Yet another trap is that 2-bus processing can be confusing. Again with the EQ example – if you’ve boosted the bass, you might be working on a background part and be wondering why the frequency balance is skewed, when you might not have any EQ (or even different EQ) on the channel itself. With 2-bus compression, instruments will sound different when solo’d to when they’re in the mix – sometimes radically so. 

The other issue is the confusion between 2-bus processing and mastering. As I’ve mentioned before, 2-bus processing is what happens when you insert plugins on the stereo pair that goes out to your speakers. Mastering is what happens when you prepare a stereo mixdown for a distribution format or medium. If you’re inexperienced, it can be easy to try to do both at once, when they really are completely different tasks (that happen to use similar tools). In short – mixing is the process of making the individual tracks work well together, and mastering is the process of making the overall sound work well in context (often next to other songs). By using mastering tools like EQ or compression on the 2-bus while mixing, it can be easy to fall into the trap of making mastering adjustments before the mix is finished. Of course, these mastering adjustments are undermined when you go back and change a mix element, which means you have to go back and change the mastering adjustments, and so on and so on. 


Mixing without 2-bus processing – for

This is the “traditional” approach. Without 2-bus processing, the mix is much more controllable, and allows much more precision in making mix decisions. You hear the individual tracks as they are. The EQ and compression settings on each track actually reflect what you hear. Adjusting the levels or EQ of a single instrument doesn’t magically adjust the levels or EQ of other instruments. You don’t have to worry about mastering taking your focus away from getting a good mix. You can master when the mix is done without worry about later mix decisions messing up your mastering adjustments. Soloing instruments is a good way to “zoom in” on a sound, while still having the confidence that the sound won’t change when the other instruments are brought in. 


Mixing without 2-bus processing – against

Of course, the downside to mixing without 2-bus processing is that you can’t hear the effect of any processing you might be planning to use. As I wrote earlier, this is particularly important where 2-bus processing (such as pumping compression) is a significant part of the character of the overall sound. Unless you’re quite experienced, it can be difficult to balance the instruments to hit the compressor in just the right way. It’s even more difficult if you can’t even hear the compression because it’s not plugged in! Regarding EQ, sometimes drastic EQ adjustments in mastering can reveal unintended sound elements. Mixing without such eq, it can be difficult to predict what mastering might bring out (or suppress). Arguably though, this can be mitigated somewhat by targeting your mix to be close to your target frequency spectrum. Close enough only – don’t get surgical – leave that for mastering! 


What I do

As a general rule, I mix without any EQ or compression on the 2-bus. Pumping 2-bus compression is not something I’m particularly fond of (for my own work). I prefer dense multilayered productions, which end up with very subtle and precarious balances between instruments. Mixing into a compressor would make this almost impossible for me. Similarly, with EQ I try to mix as close to the final spectral balance as I can in the first place without resorting to global EQ. EQ fine tuning is done during mastering, and I very rarely need to make an adjustment greater than +/-6dB. 

On the other hand, I don’t shy away from using 2-bus processing for “special effects”. I’ve used filters, stereo width manipulation, buffer stutter effects, even distortion and bitcrushing. These are “special” though, and usually only engaged for specific sections of a song. They’re usually automated too, for extra fun.

-Kim.

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  1. June 10th, 2009
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