When I first started mixing, I didn't do any processing on the mix bus. Now I don't mix without my favorite plugins pre-installed on the session. After leveling the different instruments with my pre-set plugins, my mixes have a respectable low end and a nice touch of brightness – and all this before I have even touched the individual instrument tracks!
So what mix bus processing is best for mixing music? The Mix bus chain processing can be broken down into these areas:
Standard DAW plugins are usually more than up-to-the-job. However, a multitude of other plugins that can be used in the chain.
Different music styles demand different kinds of processing, but from my own experience, the mix bus always starts off and stays the same, with minimal tweaking. Mixes using the processing above give my music an excellent low-end, an appealing bright sounding top end, a pleasant stereo image, and a warm sonic character.
Insert plugins on your mix bus in this order:
The first insert on the mix bus is compression. Use the mix bus compressor to glue your mix together - or to pump if that’s your thing!
To Glue: Use a ratio of about 1.5 to 1 (do not exceed 2 to 1). Use a slow attack and slow release. Set the threshold, so the gain reduction is no more than 3dB - for most of the time anyway. Add about 2dB of makeup gain.
To Pump: Use a higher ratio, faster attack, and faster release. For pumping your mix gain reduction of about 7 or 8dB is okay.
Sidechain: For added control, optionally feed a sidechain signal into your compressor. Use the signal that feeds the mix bus and apply an HPF, filtering out the low frequencies, so the compressor doesn't react as much to bass guitar and kick drum.
Add some coloration to the mix with a tape, valve or transformer emulation plugin. There are a lot of choices out there but remember to apply this effect in moderation. As with a lot of processing in mixing, less is more.
Use a mid-side EQ to add a high shelf filter of 1.2dB to 1.4dB at 8kHz to the side of your mix. This filter will apply to the right and left channels and will provide some pleasant air and space for your mix.
Attenuate 1db at 300Hz with a broad Q, to the mid-channel only. Boost 1dB of 60Hz with an equally broad Q to the mid-channel.
The EQs acts as a preset tone control which, in most cases, adds instant low-end and brightness to recorded material. The EQs apply to all your tracks, so you shouldn't need to add much more processing to the individual tracks.
Aim to take the stereo image out another 20% each side from the hard panned position. Stereo width is principally achieved by duplicating a copy of a signal from one stereo channel and mixing it back into the other. There is often a little processing ‘magic’ that can occur too, for example, reversing the polarity of the combined signal or delaying it slightly to widen the sound. There are numerous plugins available for stereo widening.
At the time of writing, Izotope provides their Ozone Imager for free, which is highly recommended. Paid alternatives are Soundtoys’ Panman or Microshift, Waves Reel ADT or Imager and, Eventide's Ultra Channel.
Figure 1: Izotope Ozone Elements Stereo Imager
Also knows as the smiley face EQ, this stereo processing applies a low end and high end to both channels. Apply 3db at 100Hz and 4db at 10Hz. Use a very open Q.
Figure 2: Waves PuigTec EQP-1A Smiley Face EQ
In the digital world, we suffer from perfection. Perfect sound can be recorded, perfect images can be created, and digital machines and software are made to manipulate our digital data. The problem is that, as humans, we prefer imperfections. I don’t mean huge flaws but subtle ones.
When Pixar, the makers of Toy Story first created Woody and Buzz Lightyear the animators made the characters skin tone and color perfectly smooth and consistent. The light and shadow created by the animation were programmed to change the skin color based on their advanced rendering algorithm. When the team of animators saw the rendering for the first time, they were stunned!
The characters that had looked so good on the storyboards looked, well, weird! The faces and hands were too perfect. They soon realized that the lack of imperfections on the skin was causing this problem. So they set about adding flaws to the digital skin, and the results were more realistic looking characters. As humans, we have a natural bond with imperfection.
In the same way, when we record audio in the digital world, we capture an almost faultless version of the sound. And when we play it back through our digital workstation, we get a similar result to Pixar, music that is too perfect, that lacks color, character, and warmth. In the analog world, the imperfections are added with the machines and hardware that are used to record and mix.
Adding imperfections to recordings is done with Harmonic Distortion. Noise is added at frequencies that are ‘related’ to the original source. This is a complex subject in itself and better left for another article. For now, let's just take a look at the 3 main types of distortion that could be considered for you on the mix bus.
Figure 3: Waves Kramer Tape
What is the best mix bus chain for mixing drums? After double checking any phase issues from the source material and fixing any substantial performance issues send all of your mono and stereo drum tracks to a drum bus. Send one copy of the bus through an aux track with your favorite room reverb and send that output to a master drum channel. Create a second auxiliary track and send the drum bus to that too. This will be for parallel compression. Compress this signal to taste, but you can really crush it here, and blend the sound of the original tracks with the reverb and parallel compression track. Try scooping out about 5dB of 470Hz on the master drum channel to remove room resonance.
What level should I mix in the mix bus? Mix at the K-20 standard. 20db gives more than enough headroom for the mastering engineer to produce a great sounding master. The K-20 system provides a sufficient amount of headroom (20dB), so you won’t need to be worrying too much about levels creeping up while you are mixing. Just make sure you keep an eye on the signal going into the mix bus compressor, you may need to adjust the threshold occasionally or set up a master fader to ‘feed’ the mix bus – alternatively, try adding an ‘empty’ aux track in the chain to act as a meter. If your recorded tracks are too hot for the K-20 metering, trim them down individually with a trim plugin or reduce the gain in each clip.
What other mix bus plugins sound good? Standalone plugins are made by many of the market leaders. Izotope have a suite of plugins under the Ozone brand that provides some elegant and user-friendly tools for the mix bus chain. Waves offer their, Abbey Road modeled, EMI TG12410, which includes mid and side processing, compression and limiting. Softubes Drawmer S73 is a highly regarded multiband FET styled stereo compressor for use on the mix bus – this plugin comes free in the ‘Time and Tone bundle’ if you have a Focusrite USB Audio Interface. The Sonnox Oxford Inflator is designed to increase loudness without any artifacts and works particularly well at the end of a mix bus chain.