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Mixing Theory: Why can’t I hear everything?

How do you think about a mix? In conversations with other musicians who don’t do much mixing I often find they think about mixes in a very linear fashion. Mixes are anything but linear in nature. This article presents a non-linear way to visualize a mix. The concept can be hard to grasp on first read but tuck it into the back of your mind as you do your mixes. Once you get a chance to match your experience with this concept you will find your mixes start to open up and become a bit more three dimensional.

Conventional Mix Visualization

It is quite natural to think of a mix laid out as a bunch of individual tracks. The mix is made up of individual tracks after all. Mixing boards go a long way toward perpetuating this school of thought because of their layout. You have a fader for guitar, a fader for bass, a fader for vocals, etc. Any one of these faders can be set at any point from bottom to top. As long as you are not at the bottom or top of the fader you are free to turn an individual track up or down.

This tends to result in us seeing a mix the same way a mixer does (see Figure 1). Each mix element has an apparent loudness that we can think of as a vertical bar. We say apparent loudness because our hearing a mix has much more to do with psychoacoustics than actual measurable volume. In short, our ears do not hear the same way our eyes do. We’re going to use Figure 1 as the target mix for this example.

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Figure 1: Easy mix visualization

Now we know what our mix target looks like in our ears, how can we get there? Our starting point will be Figure 2. The first thing our ears might notice is the keyboard. It is very hard to hear over the other instruments. The bass also sounds like it might be a bit low but we will start working on the keyboard because it needs the most help. How do we help it? Because our brain and eyes are working against our ears, the first impulse would be to increase the volume of the keyboard. Years of staring at mixing boards have taught us that is the answer. Grab that keyboard fader and push it on up a bit.

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Figure 2: Mix starting point

Something interesting just happened (see Figure 3). The keyboard did get louder. We have a problem though. All the other instruments got quieter. This might seem natural (increase one, all other seem to decrease) but that is not the interesting part. The unexpected result is not only did all other instruments seem to decrease in volume, but they changed their apparent loudness in relation to one another. Increasing the keyboard did not just make the vocals harder to hear. The guitar is now covering the vocals up more than it was before.

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Figure 3: Mix after adjusting keyboard fader

New mix visualization

This is due to psychoacoustics which we mentioned earlier. Psychoacoustics is a deep and complex field but I can sum it up in one sentence for you. What our conscious brain and eyes “hear” is not related to what our subconscious brain and ears hear. Restated: the way we think about sound has nothing to do with the way we hear it. A more effective way to think of a mix is like a pie (see Figure 4). The size of a piece of pie illustrates the apparent loudness of each mix element. This technique makes it easier to see how how we make the keyboard louder. Something else has to get a smaller piece of the pie.

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Figure 4: Better mix visualization

This is a very good way to think of your home studio mix (or pro studio mix!) because it gives a great sense of how adjusting one track affects other tracks. The even greater implication is a bit more subtle. Any mix has a finite amount of space it can take up. The mixer/track based mix visualization gives us the idea that we can just keep increasing volumes of individual tracks until it sounds right. The pie tells us a different story. A mix has a set amount of headroom that you can not ever go over. It is not possible to take Figure 3 and increase the vocal level, then increase guitar level, then turn up the bass, then turn up the vocal, then turn up the drums, then turn up the guitar, etc. because you will soon find every track clipping and your mix still sounds terrible. With the circle you can more easily realize it is not possible to go outside the extent of the mix. You can’t just make a bigger pie, you’ve got to divide up the one you’re given into appropriately sized pieces.

Coming of age as an audio engineer

This article has kept things fairly simplified by using volume as the only way to alter an instrument’s balance in the mix. In reality the interaction between instruments is much more complex. As an example, I relate a story of an early a-ha of my own.

The first mix I ever did with more than four tracks gave me lots of trouble. It took me months to mix it (and I still can’t stand to listen to it). I spent endless hours every day tweaking each and every track, getting frustrated my song didn’t sound like those of my favorite artists. One particularly troubling instrument was the snare drum. Snare drums on albums (at least the kind I like) jump out of the speakers and smack you in the head. I just could not get my snare drum track to do that. During one of my dozens of mixing sessions on this song I decided the hi-hat was just a bit too loud. I tried lowering the hi-hat track by one decibel. I was instantly surprised at what I heard. The hi-hat had not changed volume at all. What did happen was the snare drum suddenly jumped out of the speakers just a bit more. This experience was the beginning of developing this way of thinking about a mix.

Sometimes when you want to adjust your guitar, you actually have to adjust the keyboard. Sometimes if you want a louder vocal you need to change the drum overheads. There are no hard and fast rules about these sorts of things and only experience and hands-on mixing in your home studio can get you the intuition on how to approach it. Please also don’t take away the impression that volume is the only factor. You might need to change EQ, reverb, compression, volume, pan, etc. to change your instrumentation in the mix (and maybe not even on the track you’re trying to affect). To complicate matters, you might find adding reverb to the snare brings out the toms in one mix but hides them in another. Don’t back down! Just keep mixing and thinking about this and before long you are going to be cranking out pro sounding mixes to be proud of.

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