Anyone who has ever tried to mix recorded music knows that it can be a confusing process. You think your mix is sounding great, then the next day you play it in the car and it's totally whack. There are a lot of reasons for this, but I want to focus on one in particular that is extremely counter intuitive.
The main task of mixing recorded music is to balance the relative volume of the sounds in your mix. We all have the ability to perceive relative volume; it is simply ascertaining whether a given sound is "louder" or "quieter" relative to another. Mixing live music is also about adjusting the relative volume of the sounds or instruments in your mix. But, among others, there is a significant difference in a live mix. A live mix is also greatly concerned with the absolute volume of the mix elements.
As humans we have strong abilities to perceive relative volume and absolute in tandem. On the other hand, I don't think we have intuitive abilities to understand relative volume as an element of sound separately.
A simple example will illustrate. In a live mix (at a concert for example) when you turn up one mix element, let's say the lead vocal, it is perceived as both louder relative to the other sounds. On an absolute level, it's just plain louder! The mix is only listened to once (it's live) so what you hear is what you get.
To contrast, in a recorded mix you only have control over the relative volume of mix elements. This is because you have no control over how loud a listener will play the mix or in what type of acoustic environment.
This leads to some very counter intuitive results. Let's say you are mixing a recording with bass, drums, guitar, and voice (keep it old school here). As your working, you decide the voice just has to be louder. If you have other people in the room, they might all agree, "turn the vocal up!" As you are sitting at your mixer/workstation, if you push the fader up on the vocal it will indeed be louder on both absolute and relative terms. Since it is trivial to change the overall level of a mix at the last stage (the master fader), the concept of relative volume means that turning the vocal up is basically equivalent to turning the bass, drums, and guitar down! If your mix helpers say "turn the vocal up" and you turn to them and say "oh, you mean turn down the bass, drums, and guitar" the will almost certainly not agree that is what they want.
This is a very practical concern when mixing music with vocals. It is usually a concern to get the vocals loud enough to be understandable. At the same time, pop music often demands that accompaniment tracks sound "loud" as well. This is really hard to get your mind around. We just don't understand sound that way. Louder is louder in our minds and bodies.
This means that to become a skilled mixer of recorded music, you need to learn specific ways of understanding what it is that you are hearing as you mix, and how that relates to your final mix. It's harder than it looks:)
A fundamental aspect of this difference between mixing live vs recorded music is that in live mixing, you are really mixing sound. In recorded music you are manipulating data, the sound you hear from your monitors is just a tool to help you in that process.
Since I mostly work in the studio, this post is written more from that point of view. Live music mixing has plenty of counter intuitive and challenging aspects that distinguish it from recorded mixing! In future posts I will share some specific methods to help overcome the dilemma of having only relative volume to work with in a recorded mix.
Happy mixing!