The View from 2005: I like to think that this is one of the more “important” articles that I’ve written – it suggests a way of thinking about multitrack mixing that transcends the basic idea of just getting each instrument to sound good, whatever that means. Rereading it now, I realize that I’ve learned a lot in the interim, and there are some things that have dramatically changed in the way I approach EQ. Nonetheless, I still believe that what I had to say here is of bedrock importance to mixing and audio production. Figures 1 and 3 get handed out in almost every class I teach. And, naturally, this all plays a big part in my book Total Recording, and it is spread throughout various parts of the book.

When I taught basic audio at Berklee, I often referred to a concept I still call “the audio window,” which can be roughly characterized as the set of physical ranges within which we perceive sound. This is a useful way to think about the physical limits of musical sound.

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	Figure 1. The Audio Window - frequency versus amplitude versus time. Audible sound exists within this set of ranges, but doesn’t completely fill it (especially at low frequencies and levels). The relative proportions are not well represented -- the frequency range is a thousand-to-one, while the amplitude range is a million-to-one (a thousand times greater) and the time range is about half-a-million-to-one.

I’ve included three axes in this window, which represent frequency amplitude and time. Time merits extensive discussion, but for this article, we will concentrate on frequency and, to a lesser extent, amplitude. The horizontal axis of this window is frequency, and its range (20 Hz. to 20 KHz.) is the audible spectrum or range of frequencies that our ears can detect. This spectrum is the framework upon which pitch (melody) and timbre (sound quality) are hung. It is the most important element of the window, musically speaking, and in recording we must take immense care not to change it inadvertently or to lose part of it through careless practice or the use of mediocre equipment. But more than that, we must learn how to work within the spectrum, how to use its features and qualities to musical advantage and effect. To do this, we need to take a closer look at the spectrum itself, how we perceive it, and its musical qualities. Then, we can discuss some techniques for making better recordings by manipulating the spectrum, a set of activities I call “spectral management” (a academic power term you can use for intimidating your friends and associates in bars, pool halls, and record stores).

Before we get too far into this, the first thing you’ve got to know is that we hear in relative proportions, not absolute quantities (the academic power way of saying this is: “We hear exponentially, not linearly!”). The basic unit of frequency is the octave, which is a doubling of frequency. Octaves all have the same apparent dimensions for us humans, but in fact each higher octave has twice the range of frequencies.* In a linear quantity system, midway between 20 Hz. and 20 KHz. is approximately 10 KHz. In an exponential system, the midway point is approximately 600 Hz.

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	Figure 2. Linear and exponential (sometimes called logarithmic or log) scales showing the range between 20 Hz and 20 KHz. divided into 10 units. The arithmetic is a little sloppy in order to make the scales a little more user-friendly.

The bottom of the three scales is the most important one for us here, because it represents the 10 octaves of the audio spectrum - the raw materials of frequency out of which we build music. These ten octaves are all we’ve got, and each one has its own particular characteristics, quality and musical significance. In recording, the handling of these octaves is one of our primary working procedures. It is the basis of creative equalization, for instance. So, let’s take a closer look.

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	Figure 3. The Ten Octaves of the Audio Spectrum. Given both in terms of the ISO center frequencies (on left) and boundary frequencies. Each octave has its own particular qualities, musically, acoustically and psychoacoustically.