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Making The Most Of... (Part 12)

Stereo

Article from Home & Studio Recording, April 1986

A brief look at the difference between true stereo and panned mono with a few mixing hints thrown in.


When is stereo really stereo? This may seem to be an obvious question but you may be surprised to know that most of the pop records you have been listening to consist largely of panned mono. What's the difference? Read on.

Most people associate stereo as being something that comes out of two speakers and ends up going into two ears, but let's forget that recording was ever invented for a little while and see what's really going on. Firstly, why do we have two ears at all? Is it really just to keep our spectacles from falling off or is there a deeper reason? You probably know the answer to this one already and the reason is of course that having two ears helps us to deduce something about the location of a sound source without having to bring our vision into play. How our ears do this is not so obvious and the explanation that springs immediately to most people's minds is not the complete answer. That is that each ear will receive a different level of sound depending on whether the sound source is nearer to one side or the other. True, if someone yells in your left ear you know which side he is standing on but the way in which the brain interprets these signals is much more complex than that.

Haas Effect



Because our ears are physically separated by several inches, a sound originating at one side of us will reach one ear before it reaches the other and though this slight delay cannot be perceived as such, the brain uses it to evaluate direction. This is particularly useful in a reverberant environment because the complex reflected sounds may well confound any evaluation that relies purely on sound intensity. However, the direct sound reaches our ears a fraction of a second before the reflections do and so the direction can still be estimated. Quite how our brains do this processing is not entirely clear (which is the scientists' way of saying they haven't a clue) but what matters is that it works and this is called the Haas effect after a man who admitted that he hadn't a clue. The effect also comes into play when sounds are reflected from the floor upon which you are standing and we subconsciously deduce all sorts of directional information that tends to be largely ignored because we rely so much more on the input from our eyes.

A blind person however, has no visual sense upon which to rely and so he or she extracts much more information from sound than does a normally sighted person, to the extent that it's possible to judge when a solid object is being approached by analysing reflected sounds. Again this is not done consciously but it does demonstrate that the processing carried out by the brain is very complex, it can even react to the Doppler pitch shift of sound reflected from a moving object. Anyway, all this has been going on for millenia, no doubt as part of our survival mechanism - and then someone came along and invented stereo recording.

Stereo



The theory is fairly simple. Just use a pair of microphones to capture what would normally be received by the average pair of ears, record it, and then use a pair of loudspeakers or headphones to recreate the sound at a later date and direct it into said pair of ears. As you will probably be aware, this is only a partially successful system as you can tell by the number of dissatisfied audiophiles doing experiments with dummy head recordings and surround sound but it works surprisingly well, at least as far as the average record buyer is concerned.

So all progressed peacefully for a few years, engineers stuck up two mics, the band or orchestra played and there it was, the finished stereo recording. Then the multitrack was invented and, because there weren't enough tracks to record every instrument separately in stereo using two mics, some bright spark invented the pan pot so that a signal could be recorded in mono using one mic and then panned to any point between the two speakers. This takes us back to the initial and incomplete assumption about the mechanism of the ear where it was assumed that only sound intensity was used to analyse direction. As it turns out, panning a mono sound does alter its apparent location but the vital delay clues are not accurately reproduced and the result is not really convincing except in a rather superficial way. Still, the listening public who were generally satisfied with a cereal packet containing a three inch speaker were more than chuffed. So the early stereo records contained wild panning effects just to entertain the audience; just witness some of the early Jimi Hendrix records!

And Now



With early multitrack you were lucky to get four tracks but now that 24-track is commonplace, it's often possible to designate a pair of tracks for a true two mic stereo recording and pianos are frequently recorded in this way as are most classical concerts. However most things are a mixture of true stereo and panned mono, a typical example being the drum kit. Normally the drums are close miked with the snare drum and bass drum being panned to the centre with the rest of the kit arranged across the sound stage using only the panning controls. On top of this, there may be a couple of so called ambience mics or overheads which pick up the overall sound of the kit (including some reflected sound from the walls and floor) in true stereo. When this is all mixed together it sounds quite impressive but does it sound real?

One analogy that I like to use is that our two ears judge the distance and direction of a sound source in much the same way as our eyes focus on things and deduce the size of objects. After all, we use both our eyes to judge distances using parallax. Panning a mono sound to give a sense of direction is almost akin to looking at an object with one eye and then increasing the size of the object to fool us into thinking that it's nearer.



"Avoid the temptation to pan the two sides hard left and right as you may well end up with what sounds like a twenty foot wide piano."


So if a mix is created by adding different stereo recordings of individual instruments with some panned mono thrown in, what exactly is the result? To use the visual analogy again, we have probably got the equivalent of a painting where some of the houses in the background are larger than those in the foreground, some of the shadows fall to the left and some to the right, and everything focuses in the wrong place - quite a recipe for eyestrain.

Fortunately, discerning as our ears are, they are a lot easier to fool than our eyes and so an entirely synthetic mix can sound quite acceptable. I still feel however, that mixes of really incompatible sound sources and treatments could lead to the aural equivalent of eyestrain which is of course listener fatigue.

Synthetic Ambience



One way of creating the effect of space is to pan your mono recording of an instrument hard to one side and feed a delayed version to the other. A few milliseconds of delay will cause the previously mentioned Haas effect to come into play and you will be tricked into thinking that the sound comes from the side without the delay.

The other approach is to use a stereo reverb to synthesise a convincing acoustic environment when fed with a dry mono source and this can be very effective. Again though, engineers tend to add different levels and characters of reverb to different sounds within the same mix which all adds up to a strangely distorted sound picture. In theory this should sound awful and the classical audiophile will probably say that it does. However, the record buying public likes it and that is what counts.

What You Can Do



Panning and other tricks can be used tastefully to create a sense of width and depth in a recording but you have to take care not to do anything gross unless you need a gross effect. A better title for this section might be 'What You Shouldn't Do'. It was all very well in the early days swinging a guitar solo from side to side because then it was a novelty; now it's often just a recipe for nausea. A more subtle approach might be to leave the guitar panned to a fixed position and pan a delayed or echoed version across the soundstage, either manually using the pan pot or automatically using an autopanner. Panning the reverb associated with a particular sound can also be very effective and again, an autopanner running at the same tempo as the song can sound good.

Accepting that you will often use pan position to locate sounds within a mix, what are the rules, if any? Well there are no hard and fast rules, only ideas and preferences, but a natural sounding mix will also take account of front to back perspective as well as width. For example, sounds that are supposed to be close to the listener will have less reverb than sounds emanating from further away and similarly, distant sounds are not likely to have as much left/right information as close up sounds. This is because you would, in real life, hear more direct sound from a person talking a few feet away from you than you would from a person at the other end of a large hall where a lot of the sound would be reflected from the walls, ceiling and floor. By the same token, distant sounds contain less high frequency information than nearby ones because air absorbs high frequencies more readily than low ones. It follows that you can simulate this using your EQ to brighten up the sounds that you want to sound close up and to mellow the more distant sounds.

In purely practical terms it's a good idea to put bassy sounds such as the bass guitar and the bass drum near the centre of the mix for two reasons. Firstly very low pitched sounds start to sound omnidirectional due to the longer wavelength making any attempt at positioning ineffective, and secondly, bassy sounds need a lot of power so it is a good idea to spread them over both speakers in order to get the maximum level out of the system without distortion. There are other reasons associated with the mechanics of record cutting but they are beyond the brief of this article.

A typical mix might have the bass, snare drum and vocals located somewhere near the centre with the toms and cymbals spread across the width of the soundstage. Other instruments might then be moved towards either side to create a hole in the middle for the vocals, and if two sounds occupy similar parts of the audio spectrum, it is a good idea to pan them to opposite sides in order to give the listener the best possible chance of separating them. Likewise, if you want to create a sense of movement, try panning the instrument to one side and putting an echoed or reverberated version at the other side. In this way the sound will move every time a note is played.

If you do have a true stereo recording in the mix such as a piano or even the drum kit, try to avoid the temptation to pan the two sides hard left and right as you may well end up with what sounds like a twenty foot wide piano or kit. Close your eyes, listen carefully to the mix and ask yourself 'Am I convinced?'


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Publisher: Home & Studio Recording - Music Maker Publications (UK), Future Publishing.

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Home & Studio Recording - Apr 1986

Donated & scanned by: Mike Gorman

Topic:

Mixing


Series:

Making the Most of...

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10 | Part 11 | Part 12 (Viewing) | Part 13 | Part 14 | Part 15 | Part 16 | Part 17 | Part 18 | Part 19


Feature by Paul White

Previous article in this issue:

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