Stereo Placement: Beyond the Panpot

Sure, you can do a lot of neat stereo tricks with a panpot—but it's not the only way to conjure up some stereo mojo

By Phil O'Keefe

I'm a stereo freak. I just can't seem to get enough of it, and I love it when things move, spin and fly around the stereo sound field - that is, as long as it is musically appropriate; but that's a subject for another day. Let's look at stereo placement and various ways to position sounds within the stereo field.

WHAT IS "STEREO" ANYWAY?

The way the brain interacts with our two ears and processes the sound waves that are received by them allows us to spatially localize sounds and determine the direction they are coming from - with some limitations. Some sounds, such as very low frequency sounds without a lot of overtones - such as distant thunder - are difficult to localize. But with midrange and higher frequency sounds, our ears and brain do a reasonably good job at spatial localization. The ridges of our outer ears - called the pinnae, reflect and direct sound into the ear canal, and help us to locate sounds coming from the front and rear. Our brain also uses arrival time differences to determine location - sounds coming from the left will arrive in our left ear a small fraction of a second before they reach our right ear. But neither ear works in complete isolation - in our daily lives, it’s very uncommon to hear sounds isolated in only one ear without hearing some sound in the other ear. Also, due to the acoustical masking effect of our head and the attenuation of sound levels at greater distances from the sound source, level differences also come into play in how we locate the direction a sound is coming from; although again, lower frequencies are more difficult to determine directionally. Armed with a basic understanding of how we perceive sounds, we can put that to use in our mixes.

PAN KNOBS

The first thing many people reach for when they want to place something in the stereo sound field is the pan knob. Rotate the pan knob left on a mono track, and the audio from that track moves progressively further to the left in the sound field, with more of that sound coming from the left speaker, and less from the right as you turn the knob further to the left. Sounds simple, right? Actually, it is... but panning isn’t the only stereo positioning tool in the arsenal.

STEREO TRACKS

Pan knobs are fine for positioning mono tracks, but what about stereo tracks? Some people will take the left and right outputs from a stereo keyboard and pan them hard left and right, and then do the same with the doubled guitar parts, and the drum machine tracks and background vocal tracks... and then they wonder why their mixes lack clarity and why it is difficult to hear individual elements of the mix. It's because they've got everything stacked on top of everything else! Parts that come from the same location in the stereo field will tend to blend together into a composite sound instead of discrete, individual sounds. Panning things to the same spot can be useful when you're trying to blend sounds together, but counterproductive for getting stereo separation. Instead of automatically going wide with every stereo source, I recommend finding a separate location in the sound field for various different musical parts and limit the amount of parts that share the same location in the stereo field.

You can use the pan controls on a stereo track to adjust their location in the mix in various ways. Narrowing the width of a stereo track via panning is relatively easy - instead of panning hard left and right, try setting the pan controls to 50 / 50, which will narrow the image but still keep it centered in the stereo field, or 25 / 75, which will be equally wide but will move the image further towards the right. Pan the keyboard 75 / 25, the background vocals 25 / 75, the drum machine 50 / 50 and the guitars hard left / right, and the individual sounds will become much easier to hear than if you just panned them all hard left / right, because now each will be occupying its own individual sonic real estate.

THERE'S MORE TO LIFE THAN JUST THE PAN KNOB

There are other ways to adjust the positioning of stereo tracks beyond just tweaking their pan controls. One way of manipulating the width of a stereo track that is sometimes overlooked is by adjusting the relative volume levels of the left and right channels. Try gradually lowering the volume of the left channel of a stereo file by 6 dB and listening to what happens to the stereo image - it should move further to the right as you decrease the left channel level. If your software does not have individually adjustable level controls for the left and right sides of a stereo track, you can usually "split" the stereo track into two mono files and proceed from there. When working with Mid-Side (M-S) stereo tracks (Basics Of Mid-Side Recording http://www.harmonycentral.com/docs/DOC-1722), lowering the "side" channels from the bi-directional mike will make the stereo image narrower, until you're finally left with nothing but the mono signal from the center cardioid microphone.

You can also adjust stereo positioning by using arrival time differences - using delays to move the signal further left or right. If you insert a short delay plug in on the left channel of a stereo track and adjust it for 100\% wet (full delayed signal) and set the delay time for 10 - 20 ms or so, the image will appear to come more from the right side. The longer the delay time, the wider the image will sound, but beyond a certain point longer delays will start to sound like discrete echoes instead of a stereo image.

Short delays of this type are also commonly used to create pseudo-stereo from a mono source, by using either a mono to stereo plug in and applying the delay to only one side, or by using an aux send to route the signal from a mono track to a short delay and then panning the aux return channel to a different location than the original source track's pan position. Remember to check your phase relationships by occasionally listening in mono when using this method, and if you hear the sound get thin or weak, try a slightly different delay time or hitting the phase inverse switch on the aux return channel or the delay plug in. Other useful plug ins for creating pseudo-stereo images from mono sound sources include modulation style processors such as chorusing or stereo flangers, as well as using different EQ filtering on the left and right channels. Try taking a track, making a copy of it, then rolling off the highs on one and the lows on the other and panning them in different locations. 

Feel free to experiment with combinations of these various techniques. In Fig. 1, I have used 75 / 75 panning on the stereo acoustic guitar (tracks 1 / 2) to narrow the width a bit, along with a short 12 ms delay on the right channel (track 2) to move the image to the left a little more.

Figure 1: Examples of various stereo placement techniques

Some plug ins, such as  Voxengo’s excellent (and free) Stereo Touch (AU / VST) plug in uses a combination of delays, EQ filtering and panning to create pseudo-stereo from mono tracks. You can download a copy at http://www.voxengo.com/product/stereotouch Track three in Fig. 1 is a mono background vocal that has a mono to stereo instance of this plug in inserted, and the pan controls are set to 25 / 100 to put the image more towards the right, and thus into a different location in the sound field than the acoustic guitar.

Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Associate Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.