Careful stereo placement of the sounds within a mix can greatly enhance the effectiveness of a recording. Paul White sets out the ground rules, along with some tips for breaking them.

We live our lives in a stereophonic environment, and when it comes to music, a mono recording can sound rather one-dimensional when compared with the stereo version. In real life, we perceive the sounds around us via our two ears; by analysing the sounds present at each ear, the human brain can deduce a surprising amount of information relating to the direction from which the sound is coming, and to the physical environment in which it is propagating. No recording/replay system yet invented offers more than an approximation of the way in which we hear sound naturally, though a stereophonic loudspeaker system used in conjunction with stereo mic techniques can produce impressive results.

In the studio, we place a lot of reliance on the ability to pan various sounds between the loudspeakers using the pan pots on our mixers. By this means, we can position mono sound sources at various positions between the loudspeakers to imitate a natural, stereo sound field, but it pays to be aware that using pan pots alone is an extremely crude approximation of reality. The result is really panned mono, not true stereo, though most 'stereo' pop records rely extensively on panning to create the illusion of left/right spread.

Over the past decade, stereo digital reverberation units have become available at incredibly low prices, and it is largely thanks to these devices that the gap between home and professional recording systems is now so small. Again, digital reverberation is only a rough approximation of what happens to sound in a real room, but it does manage to create a believable illusion, which is what really matters. Most digital reverberation units have a mono input and a stereo output. The ones with stereo inputs tend to use a mono mix of the left and right inputs to create the reverb, with only the original sound being passed through in stereo. This means that no matter where in the mix the original signal is panned, its reverb will come equally from both sides.

I've spoken to RM readers who are worried by this, because, on the face of it, the fact that the reverb level is equal in the left and right channels tends to 'dilute' the effect of panning the original sound. It helps, when thinking through this type of situation, to compare the outcome with what happens in a real life situation, such as when music is played in a concert hall. Take the example of a violin playing at one side of the stage; the direct sound will appear to come from the violin because our ears analyse the relative levels heard by the left and right ears and the phase relationship between these two sounds to establish direction. However, the room reverberation resulting from the performance will, essentially, come from everywhere at once because the sound is continually bouncing off all the hard surfaces in the room. In other words, we have a direct parallel to the digital reverb situation, in which the direct sound appears to come from whatever point we have panned it to in the mix, while the reverb comes from both sides. It's true that this does dilute the stereo positioning of the original sound, but no more so than in real life. Furthermore, the way in which stereo reverb algorithms are designed means that the reverberant sound produces the illusion of space and depth, so the pragmatic way to look at it is that you have traded off a degree of stereo localisation for a sense of stereo space. Adding a short reverb to a panned mono sound is probably the most effective way of making it sound as though it exists in a natural environment.

Pragmatic Panning

Referring again to real life, humans are not very good at picking out the direction of very low frequency sounds because the wavelength of such sounds is very long compared with the dimensions of the human head, which results in both ears hearing virtually the same thing, regardless of the direction of the source. Translated into the world of the recording studio, this means that panning bass sounds has less apparent effect than panning middly or trebly sounds, which is just one of the reasons why bass instruments and bass drums are normally panned to the centre of the mix.

The other main reason has to do with the way in which energy is distributed in naturally occurring sounds. In most cases, the level of low frequencies in a sound far outweighs the higher frequencies, and furthermore, in sounds that decay naturally such as drums or bells, the high frequency harmonics tend to die away first, leaving the lower tones to sustain. If the majority of acoustic energy is concentrated in bass sounds, then it makes sense to pan them to the centre of the mix so that the work of reproducing these sounds can be shared equally by both loudspeakers. If we were to pan a bass sound hard left or hard right, all the load would fall onto a single loudspeaker, with the result that we could only reproduce half as much power as before without overloading the loudspeaker or amplifier.

Performance Panning

Very often we try to set up pan positions that correspond to the way in which performers might be arranged on a stage. This means placing the main vocals in the centre along with the bass guitar, bass drum and very often the snare drum too. The guitars and keyboards can be panned to either side, as can backing vocals, while the output from a stereo reverb unit is invariably panned to the left and right extremes.

If you are attempting to create the illusion of a live performance, there are pitfalls to watch out for, though. It is very tempting to spread things out in the stereo mix simply because the opportunity is there, but this can lead to an unnatural, even uncomfortable sound; if you pan the various drums in a kit, or the high and low notes on a piano, hard left and right, you can end up with the illusion of a 30-foot wide instrument! The same is true of stereo keyboard synthesizers, and though it is tempting to spread them from ear to ear, it might be better to, for example, pan one side to the left or right extreme and the other to the centre of the mix. This will maintain some illusion of stereo spread but will confine it to just half of the soundstage.

The same could also be said to be true of stereo effects such as chorus that are applied to individual instruments, though how you apply these depends on how many mixer channels are sharing the same effect and where in the mix the original sounds are panned. We have been accustomed to hearing very wide stereo effects on record for some years now, and though the results are rather larger than life, there's no reason not to use them if they work on an artistic level. However, if you are using more than one stereo effect, it might be more effective to pan one between hard left and centre with the other panned between hard right and centre.

Whatever you do, don't worry that you're not making full use of your stereo mixing capabilities simply because so many of your sounds are located at or near the centre of the mix. You only need to move a couple of sounds out to the sides to create a sense of space, and the addition of stereo reverb will greatly add to the sense of width. Figure 1 shows how several typical sounds and effects might be panned in a stereo mix.

Perspective

Real music doesn't just exist along an imaginary line drawn from left to right, yet when we pan a sound between two loudspeakers, this is exactly what we are working with. The dimensions of height and depth are missing from the equation, so we have to simulate them using other techniques. Recent work has indicated that the early reflections produced when a sound occurs in an enclosed space have a profound influence on how near to or far away the sound appears to be from the listener. Intuitively, it seems logical that a more distant sound will contain a greater proportion of reverberant sound than a near one, but the spacing and rate of build-up of these reflections also appears to be important. If you have a reverb device which allows you to create early reflections patterns, it is worthwhile experimenting with the various options and making notes of any settings that produce a definite sense of closeness or distance. Small room or closely-spaced reflections patterns seem to create a sense of closeness or intimacy, but much more work has to be done in this area before we can dispense with trial and error.