Whether you're mixing a three-piece band, a Progressive Techno masterpiece or a full orchestra, you need to know how stereo works if you want to get the most out of your music. We'll look at the aims of stereo mixing, how the technical sides of things work, a few basic ground rules and how we can use stereo to complement our mixes.

The reasons for choosing stereo reproduction over mono are quite clear: stereo allows us to hear a more realistic, more accurate representation of a three-dimensional sound than mono ever could. However, there are a number of further reasons why the ability to adjust stereo balance while mixing is highly beneficial. Primarily, mixing in stereo (i.e. the delicate art of positioning each sound from left to right in the stereo image) allows us to create a more powerful mix by making space for each element. Where two parts (say, a synth lead and a guitar part) might clash if they were both panned centrally, pushing one to the left and one to the right can give each one a bit of room, increasing the impact of both.

As such, stereo mixing techniques not only affect the obvious left-right placement of sounds, but can also increase clarity and add a sense of space around each instrument or part.

For now, let's consider a mono sound source rather than a stereo recording. Take a mono snare drum track - if we start off with it panned centrally, the sound is sent to the left channel and the right channel of the mixer output in equal amounts. The volume of the snare coming out of the left hand speaker is identical to the volume coming out of the right hand speaker, which tricks us into thinking that the sound is coming from the midpoint of the two speakers.

This phenomenon is known as the phantom center, and is crucial to the way panning works. As we pan from the center position towards the left, the level of the signal sent to the right hand speaker is reduced. As a result, the snare appears to move from the right hand side to the left. At the extreme left position, none of the signal IS sent to the right hand speaker, and so the snare appears to be situated at the far left hand side of the stereo image. This is a slightly simplified explanation, not taking into account a principle known as pan law. See the Pan Law box on the next page for the implications.

As we continually point out in Knowledge Base, there are very few hard and fast rules when it comes to making music. The old adage that it it sound right, it is right applies yet again in the case of stereo mixing techniques. Having said that, there are a couple of rules of thumb which mix engineers tend to follow and they're worth bearing in mind while you work because they'll probably save you time in achieving a good stereo balance.

The first rule of thumb relates to the way that human ear has difficulty pinpointing the direction which lower frequencies are coming from. As a result, it's common practice to keep lower frequencies closer to the middle of the stereo image, only getting more heavy-handed with the pan pot as you approach the upper-midrange and high frequency elements. This is also, to some extent, a throwback to the vinyl days, when wide-panned bass frequencies would tend to make the needle jump out of the groove.

Nevertheless, it's still a useful guideline to follow in the digital era. In fact, just by following this rule you'll usually find yourself with a reasonably good rough stereo balance, as the lowest frequencies of the mix, kick drum and bass, will be panned to the center and should hold the mix together nicely. If you also pan the vocal and snare to the center (the most important elements of a mix will logically sit in the middle in most cases), you'll find more often than not that you've created a good platform from which to experiment. Higher-frequency elements like percussion parts can handle extreme panning, then as you work your way down the frequency range you can get a bit more subtle, carving out space for guitars, synth parts and other instruments as you go.

The second rule of thumb is simply that extreme panning should be avoided unless you have a very good reason to do it. Whenever you pan anything hard left or hard right it's going to stick out, so you need to be sure that you really want it there. Often it's easy to say to yourself, 'I want this synth on the right' and crank the pan pot all the way round to the right. A lot of the time, what you really meant was, 'I want this synth right of center' and a smaller pan would have been more appropriate. To some extent, this is also true of placing sounds smack bang in the center of the stereo field. Ask yourself whether you're placing something in the center because it sounds best or just because that's the easy choice.

Simple stereo recording techniques are an incredibly useful addition to simple mono sources when it comes to creating a balanced, realistic stereo mix. In the case of a true stereo recording captured using a pair of microphones, the left and right channel will contain waveforms which differ in terms of timing, harmonic content and relative levels. Compare this to a panned mono signal, where the left and right channels sent to the mixer's stereo output are exactly the same waveform but at different volumes.

As we discussed previously, stereo mic techniques are most useful when attempting to create an accurate representation of a stereo source, so they're most commonly employed for live recordings of acoustic instruments or for capturing the stereo field produced by an ensemble. However, they're also useful for livening up synthesized sounds or adding stereo effects to a mono source in addition to basic panning and stereo mixing techniques.

When it comes to the mixing stage, the balance control on a stereo mixer channel is roughly comparable with a mono channel's pan pot. By adjusting the balance between the two channels, the stereo image can be shifted en masse from left to right.

At this point, let's take a look at how stereo effects can be used in order to add interest to a mono source. The most obvious effect can be achieved by turning a pan pot by hand, moving a sound around the stereo image as the music plays. This kind of heavy-handed dynamic panning has largely gone. out of fashion since its heyday in the 1960s. Effects like stereo delays work along similar lines, taking a mono source and bouncing it around the stereo image to provide excitement and interest. Other effects, such as widening plug-ins, are most useful for dealing with sources that are already mixed. For example, a busy mono drum loop with lots of percussion and multiple hits on each beat might be impossible to split into its component parts in order to process them individually. Adding a widener like Logic's built-in Stereo Spread plug-in can add a pseudo-stereo feel to a mono part, making it seem wider than it really is. One important thing to bear in mind is that just because a synth or VST can output a stereo signal doesn't necessarily make it worth using. In many cases, a mono signal will keep your options open further into the mix stage, and care should be taken to avoid committing to stereo effects early on in the mixing process. The worst case scenario is that your stereo synth part doesn't fit the final mix so you have to bounce it back to mono and then start adding stereo all over again.

Finally, no matter how fancy you get with the stereo mix, don't forget that it's still crucial to ensure that your tracks are mono compatible. Historically one of the main reasons for checking your mix in mono was to make sure it would sound good on the single-speaker record players, radios and televisions it would be heard on.

These days, the majority of home listeners will have stereo equipment but there's another important reason to check mono mixes. Even a badly set-up multi-speaker stereo system in a club can effectively sum your mixes so it's still well worth paying attention to what happens when it all gets added together.