Think that surround sound technology is something new? Think again. It actually made its first public appearance way back in 1941, with Disney’s groundbreaking animated film, Fantasia. Of course, there have been many significant developments since then, and today surround sound is an integral part of motion pictures, gaming and more. The prevalence of home theatres has also meant that surround playback systems have become increasingly affordable. And even though it has never quite caught on as a music-only format (at least not yet), there are still lots of new recordings being released in surround on DVD and Blu-Ray discs, not to mention remixes of legacy stereo albums such as the 2017 re-release of The Beatles’ Sgt Pepper’s Lonely Hearts Club Band and the 2012 re-release of Rush's 2112.
As you make the transition from stereo to surround mixing, here’s a look at some of the most important rules to follow... and the problems to avoid.
By far the most common surround format (and the one used widely on DVDs) is 5.1, where six output busses are required to feed five full-range speakers and one band-limited subwoofer. (The number after the dot, in this case “.1”, signifies how many subwoofer channels are being used.)
The subwoofer (which carries the “LFE,” for “Low Frequency Enhancement” channel) can be positioned pretty much anywhere in the room, since the low frequencies it generates are more or less non-directional – that is, it’s tough to determine where they’re coming from anyway.
Blu-Ray discs allow for the storage of more data, which has given rise to the 7.1 format, where two more output busses are required and two extra full-range speakers are added to the array, called “surround left” and “surround right.” These are positioned off to each side of the listener, kind of like a big pair of headphones.
There are also variations on these themes, though you’re less likely to encounter them:
5.0, which is the standard 5.1 configuration minus the subwoofer 6.1, which adds a rear centre channel 7.2, which is the standard 7.1 configuration with two LFE channels (driving subwoofers positioned front and rear) Even 10.2, which adds two front “height” channels, two front “wide” channels, and a rear centre channel.
A few years ago, Dolby and DTS introduced new “audio object”-oriented surround formats called Atmos and DTS:X, respectively. These have found favour in the cinema and gaming worlds and are incorporated in a growing number of home theatre products. Both add two or more ceiling-mounted, or upward-firing speakers for the added dimension of height. Such arrays are termed “5.1.2” or “7.1.2,” with the final digit representing the number of height speakers. Unless you’re specifically doing professional-level mixing for one of these formats, you don’t need to worry about the extra output busses and physical speakers since such channels can be derived digitally through encoding processes. A standard 5.1 or 7.1 configuration should work just fine for most Atmos or DTS:X projects.
For some projects, you want to put the listener in fifth row centre. For others, you want to put them in the centre of the band onstage. And there will be times you won’t want the listener any particular place at all.
The approach you take – realistic, hyper-realistic, or completely unrealistic – depends largely upon the project, but it’s a decision you should make very early on, even before you start mixing.
When mixing live performances for surround sound music releases, realism (or, at best, a conservative type of hyper-realism) is probably a good goal. In those circumstances, you want to pay special attention to audience microphones in order to construct a believable virtual space.
Studio recordings are a completely different animal; here, you can go for anything from “listener in the centre of the room with the musicians all around” to sounds bouncing and panning all over the place in a sonic universe of your creation.
Of course, when mixing for film or gaming, you need to be conscious of the proper positioning of the various elements within the surround sound field, and audio for film is always built upon the unbreakable dictum that dialog is king, so you need to have all the elements fit around it and not obliterate it.
Other than that, there are no hard and fast rules. One cool approach is to think of surround sound mixing as similar to using different camera angles. Sometimes getting up close and personal is best, while other situations call for a wide panoramic shot. Whatever you do, make a statement; but make sure it’s a tasteful one. Don’t just do things for shock value; make sure your mix contributes aesthetically and musically.
Years of stereo mixing have taught us that the way to get a signal to appear directly in front of us is to route it at equal strength to the left and right channels, thus creating a phantom centre image.
This still works just fine when mixing in surround, but the difference is that you now have a discrete centre channel feeding a real speaker physically located between the front left and front right speakers.
So what’s the best way to pan centre?
Well, like so many other things in surround mixing, it depends.
One factor to bear in mind is that the centre channel speaker in many home playback systems – particularly “home theatre” ones – can be entirely different from the other speakers due to space considerations and may even be voiced for speech rather than music. In such cases, audio coming from a real centre speaker exhibits a slight midrange bump as compared to a sound appearing from a phantom centre – a phenomenon that can tend to make vocals somewhat harsh.
There’s also an inherent problem with a phantom centre in that it only works for listeners in or near the sweet spot; someone seated close to the left speaker, for example, will hear the signal as coming from that speaker alone. So if someone moves around the room, signal coming from the real centre channel will remain fixed, while phantom centre signal would shift, skewing the soundstage.
For the reasons given above, you may want to avoid using either the centre channel or phantom centre on their own. The best solution often comes from using them in conjunction with other channels. Divergence – a multichannel panning feature offered by most DAWs – provides an elegant way to accomplish this. This control allows you to “bleed” selective amounts of signal from one channel into adjacent channels. So, for example, you can send all the elements you want coming up the middle to the “real” centre channel and then adjust the divergence control on those elements to bleed into the L/R a little, say at around -6dB relative to the real centre.
Before we leave this topic, let’s talk briefly about whether or not it’s possible to create a phantom centre in the rear channels; after all, surround sound systems incorporate two speakers behind you. The answer is... sort of. Signal sent at equal level to the two rear speakers will appear to be somewhat centred behind you, but with much less image stability – perhaps two-thirds of what you get from a front phantom centre. This, once again, is due to the physical shape of the human head and the placement of our ears.
One guaranteed way to ruin your surround mix is to send signals to multiple channels – especially adjacent channels such as the centre, front left, and front right channels – at equal level. Doing so will almost always result in some frequency components cancelling out, resulting in comb filtering and a very evident “hole” in your mix, particularly as you move your head around.
If you’re going to send a signal to multiple channels, either do so at differing levels, or delay the signals slightly – optimally somewhere between 12 and 48 milliseconds. The human brain registers this as natural reflections, just like in a real space, and comb filtering will be at least minimised, if not completely eliminated.
As its name implies, the LFE, or “.1” channel should be thought of as a special low-frequency effects channel. It’s also one that you shouldn’t rely on too heavily since you have no way of knowing if the user’s subwoofer is calibrated correctly, uses the same frequency crossover point as the one in your studio, or even if it is being used at all.
That doesn’t mean you should ignore it, however. Even if you don’t create an LFE channel, there’s a good chance the user (or, more specifically, the user’s system) will create one for you, which could mess up your mix altogether.
Here’s the deal: Many consumer playback systems use satellite speakers for the rear and/or surround channels – speakers that, unlike the others in the system, are not full-range and are usually quite lacking in low end response, meaning that a subwoofer is necessary to enjoy the entire signal. These systems also assume that if a subwoofer is connected, the user wants to hear rumbling. If there’s no LFE channel, bass management systems are used to derive one from the low-frequency content in the front left/right channels (and sometimes from the centre channel as well).
Regardless, it’s always best to create an LFE channel. You can simply send a band-limited mix of whatever low frequency signals sound good to you: generally, kick drum and bass guitar or synth fundamentals, supplemented by the odd tom-tom hit or explosive sound. If there isn’t sufficient low end in the various sonic elements you’re mixing, consider using a subharmonic generator, which lets you process polyphonic content to enhance low end in a natural and musical way.
Do this, and if the end user happens to have a correctly calibrated subwoofer connected, and if that subwoofer’s crossover frequency is the same (or close to) the one in your studio (80 or 120 Hz are most commonly used), they will hear the mix pretty much as you intended it. If not... well, you can only hope for the best. But at least the LFE signal will be one that you custom-created, not one solely dictated by the circuitry in their playback system.
Other than that, you can do pretty much anything you want. Here are a few suggestions:
Try putting the drums in the rear for part of the song, and in the front for other parts. Add depth to a lead vocal by routing it in mono to the centre channel, then add a little bit of it in stereo (perhaps with the use of a stereo reverb) to the rear speakers. This tends to bring the vocal out in front of the listener’s face and also spreads it out a bit without the danger of comb filtering.Try the opposite approach with instruments: Pan them in stereo to the rear speakers and then add a little to the centre channel at a much lower level to bring them forward a bit.If you have an instrument recorded in stereo, pan it hard left and right to the front speakers, then feed the signal to a stereo reverb and route the returns to the rear speakers. In a similar vein, route stereo drums to the front speakers and room mics to the rear speakers. Having dry signal come from two speakers and ambience coming from speakers in different locations can create a strong enveloping effect. In a 7.1 system, treat the “surround” speakers off to the sides as if they were an oversized pair of headphones. They represent the perfect place for you to hide that all-important “ear candy” in every mix.
If you’re like most audio professionals, once you get into surround mixing, you’ll have a hard time returning to boring old stereo. Time to push some boundaries!
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http://www.mix-engineer.com/audio-philosophy/surround-sound-mixing/
https://www.soundonsound.com/techniques/surround-sound-explained-part-7