An effective mix takes advantage of the existence of phantom images and builds a full, clear comprehensible sound stage around them. Stereo permits us to unclutter the imaginary point in space between the speakers and to creatively control the placement and movement of each track in our mix.

The basic layout of that soundstage (for generic pop and rock multitrack recordings) has evolved over time to have the following character:

Left	Center	Right
Rhythmic Stuff (HF)	Lead Vocal	Doubled Rhythmic Stuff
Stereo ambience and instruments - - Stereo Ambience and instruments
Harmony vocal	Electric Bass	Harmony vocal
Kick Drum

Figure 1. Basic locations of sounds on recorded sound stage, with lead vocal, bass and kick drum occupying the phantom image, rhythmic material panned hard left and right, often with harmony vocals as well. Stereo instruments (like piano, or string pads) often fill in as a sort of “stereo glue” to hold the mix together. Sometimes, the stereo overhead mics from the drum kit do the same thing.

This stage is often organized for particular musical effect and to make the musical impact clearer and more coherent.

We have a tendency to think that the phantom image follows the pan-pot on the mixing console, so that when we turn the pan-pot a little to the left, the phantom moves off to the left as well, hovering closer to the left speaker than the right. That pan-pot, of course, is just two volume controls, one for each of the stereo channels, with one wired in reverse so that its volume goes down as other one is turned up. The whole effect of panning is done by just varying the relative difference in amplitude between the output channels.

I used to think of mixing as the representation of the band I was recording on an imaginary stage between the speakers. I see my students today at Berklee doing the same thing when they start out. I would (and they do) very carefully set the pan-pots for all my tracks when beginning a mix: lead vocal in the middle (for instance), harmony vocals just a little left and right, the rhythm guitar well off to the left, but not really at the imaginary curtains of that imaginary stage, the lead guitar off an equal amount to the right, the keyboard player maybe a little inboard of the lead guitarist, the tambourine player just outside of the low harmony vocal, etc. It all seems pretty reasonable, my customers seemed to like it at the time and I never really questioned the whole process very much.

A little later in my mixing career I got into more simple, garage-band music that was intentionally a little raw and crude. In place of any kind of big sound, with the lush ambience of an arena or big stage, the effect we were looking for was very dry and direct, deliberately and obviously recorded in a small room, with some very hard panning to left and right, and little or no reverb except for some hard slap delays to emphasize that sense of a small room. I noticed that under those circumstances the phantom image really jumped out at me, became far more palpable and solid.

Then, a little later still, I got into some loudspeaker research, and found myself called upon one day to make a research recording, wherein I recorded a batch of clicks with very carefully documented changes in level between the stereo channels. This was one of those cases where I figured I knew what was going to happen before I started. Given my golden ears, there just wasn’t much doubt that I could hear the image move as soon as I tweaked the pan-pot even a little, so I decided to calibrate the changes to 1/10th of a decibel, so that I’d be able to really pick out the subtle differences in localization that were going to happen when the levels between channels changed. However, I was very startled to discover that the phantom image didn’t seem to move at all even when the levels between channels changed a whole decibel! I was so startled that I became positive I had made a mistake when preparing the tape! A little investigation (well, about three hours, including chasing down all the wiring in the monitoring system!) showed me that I hadn’t made a mistake, and when the dust finally settled I had found out something quite interesting: that as long as the difference between channels is less than 3 decibels, the phantom image hovers pretty much in the middle point between the two speakers. I promptly ran this down to my buddies at the local loudspeaker factory and we tried it in the anechoic chamber with blindfolds and people pointing at the imaginary phantom, and it still remained true: with up to 3 dB difference between channels (that’s half-power, remember!) the image didn’t move much, maybe five degrees. With between 3 and 6 decibels difference in levels, the phantom quickly and without much stability migrated to the louder speaker, hovering just inboard of that speaker, and once the difference was greater than 7 decibels, the phantom was for all intents and purposes coming from the louder speaker.

So, once again, I’d fooled myself, and had some new stuff to learn and think about. The principle of mixing I’ve evolved from this (not very profound, I’m sorry to say) is that there are only three panning positions: Left, Center and Right. Within those zones, the pan-pot yields a little sense of localization shift, but mostly it isn’t stable and moving my head by an inch or so screws it up. It isn’t very reliable and I can’t count on that localization detail being there in playback away from the studio.

So, you can draw some important conclusions about the pan-pots on a mixing console:

- They can almost be replaced by a 3-position toggle switch (like the ones available on any decent two-pickup guitar) labeled “Left/Center/Right.” Indeed, the first stereo consoles had exactly such a switch in place of the pan-pot.

- The pan-pot, only giving you three choices, isn’t the greatest tool for filling up the sound stage between the speakers.