• Rory Conder

Surround Sound Monitoring

8th November

Monitoring affects the recorded sound as producers and engineers react to the sound they hear.

Monitoring systems need standardisation for level, frequency response and the amount of direct to reflected sound energy.

Bass management (monophonic 5.1) is necessary even with "full-range monitoring"

Acoustical designers concentrate on balancing absorption and diffusion on the various planes.

All channels should be able to playback and have the same max volume and frequency bandwidth

Many applications call for direct-radiator surrounds; others call for surround arrays or multichannel radiators.

C, L, (30degrees) R, (30), RL(-110) RR(110) + subwoofer (LFE)

Electronic time delay is necessary to create the stereo image if loudspeakers can't be set up at a constant difference from the listening location.

  1. The LFE (0.1 Ch.) has 10dB greater headroom that any one main channel, <120Hz

All channels callibrated at the same level for video and music. For film, 3dBFS more headroom in the surround channels than the front is required.

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.

"And if you think about it, there’s something undeniably cool about being able to get up and walk around a room and hear the mix change a little as you do so. In fact, that’s something you should do every now and then while creating your surround mix: don’t just sit in your chair as if nailed there. Enjoy the freedom that surround sound brings!"

DO use divergence

For the reasons given above, you may want to avoid using either the center channel or phantom center 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” center 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 center. Before we leave this topic, let’s talk briefly about whether or not it’s possible to create a phantom center 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 centered behind you, but with much less image stability – perhaps two-thirds of what you get from a front phantom center. This, once again, is due to the physical shape of the human head and the placement of our ears.

DON’T ever send signal to multiple channels at equal level

One guaranteed way to ruin your surround mix is to send signals to multiple channels – especially adjacent channels such as the center, 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 minimized, if not completely eliminated.

Panning can work well in surround, but only between front left and right (boring!) or, to a lesser degree, directly adjacent channels; and even then, only when done sparingly and with great care. In some circumstances, you may need to boost the level of the signal as it moves towards (or away from) a particular speaker; in other cases, you may need to delay it slightly, or even reverse its phase.

DO make stereo sources mono wherever possible

Creating surround mixes from mono sources is a lot easier, and a lot more effective, than creating one from stereo sources. For that reason, consider reducing your beautifully recorded stereo piano down to an equally beautiful mono version before starting your surround mix. Ditto for stereo guitars, stereo keyboards, stereo backing vocals, etc. Doing so will allow you to construct a more impressive surround field, with a lot less need for compression, EQ, or other types of processing.

DON’T rely on bass management – especially in the user’s system – to create the LFE channel

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.

DON’T rely on bass management – especially in the user’s system – to create the LFE channel

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 center channel as well). Regardless, it’s always best to create an LFE channel. The Waves LFE360 Filter plugin provides a number of precision tools for this purpose, or 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 like LoAir, 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.

DO explore your creativity

Above all, be creative! Surround sound is a medium that positively invites exploration, even if your intended approach for a project is a conservative brand of realism. Whatever you do, try to create an immersive experience that can be appreciated from a variety of angles. Some prominent experts in the field view surround mixing as coming up with a choreography for multiple loudspeakers. Others view it as a series of stereo “planes” that run in multiple directions – not just left/right and front/rear, but between the front right and the rear right speakers, or from the front right to the rear left speaker, etc. Tools like the Waves S360° Surround Imager and Panner plugins enable the precise manipulation of imaging, distance panning, and spatial enhancement for surround sound. They can also be used to generate early reflections and employ shuffling controls to increase low frequency width and perceived depth.

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 center 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 center 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.

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