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Surround Sound Explained: Part 6

Setting Up A Surround Recording System
Published January 2002
By Paul White

Our series turns to the practicalities of setting up your own surround-capable recording system, and we talk to two radically different surround studios to see how they've coped — one at project- and one at pro-studio level.

surround header artworkHere at SOS, we're currently in the process of planning a small surround system to use as the basis for a series of practical surround articles, but before that gets fully under way, I'd like to build on Hugh Robjohns' excellent theoretical series on the subject by considering some of the practical ramifications of putting together and using such a system. Inevitably, a lot of questions arise along the way, but I'm a firm believer in explaining the questions before I attempt to provide answers!

We've also been interviewing a number of studio engineers who have been working in surround sound, ranging from project-studio owners to top-notch mix engineers at big London studios, to see how they have overcome some of the problems that arise when trying to create surround mixes with equipment designed for a stereo end product. This month sees the first excerpts from those interviews.

The increasing popularity of DVD means that many people already have surround theatre systems at home, and in addition to films and other visual material, these can now be used to play back surround audio-only recordings or music videos with surround-sound tracks. The idea is that as the domestic penetration of DVD increases, the home music system will move away from standard CD player and onto the DVD platform. Whether this will happen or not is unclear, but if it does, it will have many consequences for project- or home studio-based musicians, who until now have bought equipment designed to produce finished tracks in stereo, most commonly on CD-R or stereo DAT. If you now wish to switch to producing music in 5.1 surround on DVD, say, you suddenly have a host of new points to consider at all stages of your music-making chain, particularly if you are hoping to make the switch with as little alteration to your studio setup as possible. As we shall see, such an attitude probably isn't practical, as there is much more involved than simply adding a few channels to your finished mix! I'll start by considering how the various stages of the recording, mixing and mastering process can differ when the end result is not a stereo Red Book CD, but a 5.1 mix on a DVD‑Audio disc.

Mics In Surround

The whole purpose of surround sound is to escape the boundaries of stereo and to create music that can literally surround the listener. As with making stereo records, where source sounds may be mono signals panned into the final mix or true stereo recordings, surround productions can incorporate mono, stereo and full surround elements. The last of these are generally produced by means of microphones capable of producing a 5.1-compatible output (such as the Soundfield mic mentioned in Part 4 of this series) or mic arrays which are designed to capture the individual directional components of the soundfield (as detailed in Part 5).

Fortunately, this doesn't necessarily mean that you have to go out and buy a Soundfield microphone or a ton of extra mics so that you can use five-mic arrays on all of your sound sources if you want to work in surround, any more than you have to own stereo microphones or record everything with stereo mic arrays in your current setup. Surround microphones are used extensively in classical recording and some areas of film work, but I think it's fair to say that most of us beginning work in surround will be using predominantly mono and stereo sources, at least to start with.

Surround Mixing & Effects

Trickier to solve is the issue of surround panning on mixers designed for stereo output. Just as an engineer mixing a stereo record can use simple level panning to create a phantom image location between two loudspeakers, surround mixing can achieve the same effect in two dimensions rather than one (front-back as well as left-right) by using the multi-channel equivalent of volume panning. The main mixer control requirements for this are not just left-right panning, but also front-back panning and some means of controlling the width of signals that started their life as stereo sources.

How well project-studio equipment supports the ability to create surround recordings varies, with hardware currently tending to be less flexible than software unless you spend a lot on it (see the box below for more on the pros and cons of the software-based approach). However, much existing stereo equipment can be used within a surround mixing system, albeit with some limitations, and many of the engineers already practising surround mixing are working with equipment originally designed for stereo, as we shall see later on in this article.

The main difference between a stereo mixer and a surround mixer is that a surround mixer must have at least six busses that can be used to carry the mixed surround signals as well as a means of surround panning between them. There must also be some way of monitoring the surround busses. A number of stereo mixers have at least the required number of busses, but devising a way to change the balance of the signal feeding the five main surround busses isn't easy. It is possible to gang channels together or to use aux sends to get the required number of feeds onto the right busses at the right levels, but positioning a sound within the surround mix in this way is cumbersome. Moreover, any form of dynamic panning is virtually impossible, because of the number of controls that have to be manipulated together to create the smooth level changes needed for the appearance of a convincing sweep between surround speakers.

Some of the cheaper multi-buss digital mixers, such as Yamaha's 03D or 02R, get around the dynamic panning problem by offering a surround mode in which automatic panning is possible. You simply pick a pattern, a pan speed and decide when the effect should occur. This may be OK for some musical effects, but it doesn't offer the same freedom as something like joystick control that can be used to position sounds intuitively (interestingly enough, as I write this, Yamaha are announcing a new digital desk with a joystick panner built in for exactly this reason— see this month's News pages for more details). When positioning a sound manually on an older type of console, you generally need to operate at least two separate controls.

So, I'm not saying you can't create an effective surround mix using a hardware console designed for stereo; you just need to be aware that you will have to work within a number of limitations. The same goes for effects and processors; just as with mics, you don't need to rush out and buy specially designed surround effects processors to achieve spectacular results within a surround mix, because although such units are available (for example TC Electronic's System 6000 or Lexicon's 960L), it's possible to create dramatic surround effects by simply using two stereo units, though some lateral thinking may be necessary.

There's much more to be said on the subject of adapting existing stereo mixers and routing setups for surround applications, but the finer points will have to wait until later in this series.

Surround Monitoring

If you've been following this series, you'll know that a surround monitoring system comprises six speakers, one of which is a sub-bass or LFE unit handling low-frequency effects below 120Hz (for more details on the speakers and how they are arranged spatially, see Part 4 of this series). Of course, the first difference between this and the monitoring system you probably have at the moment is that you're going to need more speakers, and space to put them in! In the smaller studio, finding space for surround monitoring can be a real problem, but if you don't have room for five full-range speakers and a sub-bass unit, you can opt for a system that uses five smaller speakers, such as the popular Genelec 1029A (another advantage is that Genelec also make a dedicated, separate sub-bass speaker for these). However, simply increasing your number of speakers, finding a suitable sub-bass unit and arranging them all appropriately isn't the end of the story; how do you drive them from your mixer?

Unfortunately, there are few project-studio mixers currently available that offer surround buss outputs plus surround monitoring — most still only provide for the connection of stereo monitoring, even if they have some kind of multi-buss surround mode. Even assuming you have the necessary number of spare hardware outputs from your mixer, when you want to turn the overall monitor level up or down, how do you control the channels together so that their relative levels remain constant ? Adjusting several controls in tandem is not really practical.

A diagrammatic representation of a home studio surround monitoring setup.A diagrammatic representation of a home studio surround monitoring setup.If you use passive monitors, the solution is relatively affordable and straightforward — there are reasonably powerful domestic surround amplifier/decoders available with separate analogue inputs in addition to the more usual optical input, and you can connect your master surround output busses to these, and drive the speaker from the amp's speaker connections. Not only is this the most cost-effective option, it also provides you with a one-knob means of setting your monitor output level via the amp. If you use active speakers, however, the optimum setup is less obvious. There are commercial surround decoder/amplifiers that have individual line-level ins and outs, and you can use amps like these in the signal chain as described above, to drive your active monitors and control the level, but these are more expensive.

One practical, though not entirely satisfactory solution is to use the multiple buss outs (either as discrete analogue feeds or as a composite digital feed if a suitable interface card is available) from a mixer configured for surround mixing to feed a multitrack recorder such as an ADAT or DA88, which you'll be using for six-channel surround mastering anyway (more on mastering in a moment). The outputs from the recorder (which must be left in input monitor mode) are then routed directly to a set of active monitors as shown in the diagram above. Note that you could also record onto 18 tracks of a 24-track hardware recorder and then mix your six surround channels to the remaining six tracks to avoid the expense of a separate mastering machine.

Audient ASP510 surround controller.Audient ASP510 surround controller.However, the problem when monitoring directly from the multitrack outs is that when the optimum level is being fed into the recorder, the monitors will play back at a fixed level determined by how you set the trim pots on their back panels. It's quite possible to set this up for a sensible monitoring level, but there's no simple way to control that level. When you're at the tracking stage, you can turn down the mixer buss outs to feed a less-than-optimum level to the multitrack recorder, and that will bring down your monitoring level accordingly, but when you're doing your final mix to the multitrack master recorder, the level is effectively fixed as you need to record at an optimum level. Of course, if you use passive speakers powered by a surround amp (again fed from the multitrack outs), you can still control the level via the amp. Professional six-way level control boxes are available, such as the Audient ASP10, but these are still a bit expensive for project-studio use (the ASP10 retails for just under £2000). As expressed in my Leader column in August 2001, I'm still waiting for the affordable box that functions as a surround monitoring volume control.

Surround 'Mastering'

When we complete tracks by mixing them into stereo, most of us consider them finished. These days, we can even burn those stereo files to a CD-R which can then be played back on any domestic CD player. A surround equivalent to these procedures is harder to come by.

Firstly, you have to have a surround mix recorder — something capable of recording six tracks simultaneously. This isn't too difficult — six spare sequencer tracks in a software-based setup, or a stand-alone multitrack recorder capable of recording six or more channels simultaneously, like an Alesis ADAT, or Tascam DTRS machine, will suffice, provided you note carefully which track relates to which channel of the final surround mix! But playback of this 'master' is then only going to be possible from that computer, or from that type of multitrack recorder. To arrange it such that your mix can be played back on domestic systems, you need to get it onto DVD, and this requires more hardware and/or software. First you need to create files that DVD players will recognise, and for the greatest chance of player compatibility this currently means AC3 files (for Dolby Surround) or DTS files. Not only do these have to be encoded by software, there are also many settings which have no counterpart in stereo mastering — the metadata — which have to be determined at this stage, as explained in part four of this series. Dolby Digital AC3- and DTS-encoding software is available for use with Digidesign's Pro Tools, but it's still fair to say that affordable, project-studio oriented software to create these files is scarce at the time of writing, although I think it can only be a matter of time before suitable solutions become widespread.

The second part of the process involves a DVD burner to get the encoded files on to the actual disc, and again, the hardware, although falling in price, is still expensive compared to that of stereo CD-R burners.

Of course, mastering houses and the top studios have access to expensive top-end DVD encoding and production software, as well as the necessary hardware writers. If you're prepared to pay to use such facilities, you can produce DVDs from six-channel computer sequencer files or ADAT/DTRS tapes that you've prepared. However, this method is expensive, and takes the last stage out of your hands, which can be irritating if you're used to producing a finished product in your home studio yourself.

If all of this sounds impossibly daunting, it's important to remember that there are nevertheless people mixing in surround — and not just at the top end of the industry, either. We spoke to two engineers at very different ends of the business to see how they are coping with some of these issues.

Pros & Cons Of Software-based Surround Systems

Although it's not the case that hardware mixers cannot be used for surround mixing (digital desks in particular are strong candidates), it's fair to say that it's a great deal easier with software-based recording and mixing systems, as they are inherently more flexible than hardware, and the major serious audio sequencers now support surround. Adding new master busses and swathes of extra routing configurations is not a problem in software, of course, and options for burning DTS or AC3 surround audio files to DVD‑Audio discs are likely to appear in software before affordable hardware options become available. Furthermore, writing automation for level changes to create surround panning effects is much easier in software. There are even surround panning plug-ins for Digidesign's Pro Tools, such as Kind Of Loud's Smart Pan Pro. With these, you simply move a panning 'puck' around in a window representing the surround soundfield, and the plug-in works out all the necessary complex level changes to create your panning effects automatically. Surround panners for other audio sequencing systems are currently in the works or already released.

Despite these plus points, there are a few things you have to remember when adapting a software-based recording system for surround use. You need an audio output card or interface with enough outputs to handle the master busses simultaneously (ie. a minimum of six), and if you want to use external MIDI synths as well as virtual ones, you either need to add a hardware mixer capable of surround mixing back into the signal path, so that your synths can be recombined with the output coming from the computer, or you'll have to record the external synth parts into the computer as audio tracks, so that they can be part of the computer-based mix from the beginning.

Surround Case Study 1: Rik Ede's Project Studio

Project-studio owner Rik Ede is in the fortunate position of working for Dolby as their 5.1 surround evangelist. At the same time, Dolby let him run his own company, Gamesound, in which capacity he creates surround soundtracks for computer games. This allows Rik to practise what he preaches, so that when Dolby clients ask him technical or practical questions, he can reply from a position of practical knowledge rather than theory only. In fact, Rik has been experimenting with 5.1 sound ever since it became available. His work for Dolby means that he has easier access to some surround-production tools than many project-studio owners, such as Dolby Surround-encoding hardware and DVD-burning software, as well as a hardware DVD-R burner, but in some respects, the Gamesound studio is not so different from a typical project studio setup. Rik uses ordinary mics to capture his sound sources, usually in mono, and mixes using two Yamaha 02Rs cascaded together, with a Tascam MX2424 as his multitrack recorder, as he explains.

Rik Ede's 5.1 surround-capable project studio.Rik Ede's 5.1 surround-capable project studio."At the time I started writing music for 5.1, I needed a console that would have enough inputs, and the 02R was the only affordable choice that had surround panning on the version 2.0 software. Previously, I'd been using analogue consoles and routing surround via the aux sends, but the 02R seemed the best way to go."

Although most of his sound sources are in mono, Rik finds ways to make them work in surround, and hasn't yet felt the need to resort to surround effects to do it. "Dedicated surround boxes like the TC System 6000 look interesting and I've tried them out, but I've found that you can use a more affordable box like the TC D2 tapped delay, and then ping-pong the delays between the centre speaker and the rears and get very nice percussive effects. That for me is what makes surround interesting.

"When I need surround reverb, I use my Lexicon PCM80 on the front and a TC M2000 or similar on the back, perhaps delayed slightly. Even some of the 02R's built-in effects work nicely, and if you have a stereo drum loop, it can be interesting to delay the left or right signal slightly and then send it to the rear speakers via a slight pitch detune.

"To fatten a mono signal, you can use the 02R's autopan, or add something like stereo chorus at the front and stereo reverb at the rear. However, most of the time I'll keep sounds where they are and reserve movement tricks for game soundtracks. I'm stumbling across new mixing tricks all the time, and the only rule is that there are no rules, providing what you do provides somebody with a satisfying listening experience."

Rik's monitoring setup comprises five full-range Genelec 1031 nearfields, with a B&W A800 subwoofer which he uses in preference to Genelec's own sub. To get around the problem of driving his monitors, he has been using the dodge explained earlier, whereby he feeds his speakers from the individual outs of his Tascam DA38 eight-track DTRS recorder. "The 02R comes out on TDIF to the DA38, and I've taken the analogue outs of the Tascam directly to my Genelecs, which have been calibrated to a particular level that I'm comfortable with. When I'm writing material, I have control over the levels of the buss outs from the 02R, but when I'm transferring a mix to the DA38, I have to set the mixer outputs to give an optimum record level, which means the monitor level can't be adjusted. That means I end up monitoring quite loud, which is the downside of the system! However, I've recently bought a Kenwood domestic surround decoder/amplifier that I can use to feed my monitors, and with that, I can control the monitor mix level with a single knob."

Completed six-channel mixes may be recorded from the 02R either via TDIF to six tracks of the DA38 or, via an ADAT optical feed on an optional TC Unit•Y card in one 02R, into Rik's PC, where he does 5.1 mastering if he's not using a Dolby hardware encoder. "I can save my six-channel mixes as a Microsoft multi-channel WAV, which is like a single file with all six components, but I prefer to save them as separate WAV files, so that I can go in and process them separately, for example, rolling off the sub at 66Hz rather than the stock 120Hz."

For AC3 encoding on the PC, Rik uses Sonic Foundry's Soft Encode: "It's been withdrawn from sale for some reason, but it's very stable and I still use it. It has a front end that is exactly the same as a Dolby hardware encoder. You just feed in the six WAV files, set the various parameters, and hit Encode. Depending on how fast your machine is, it will encode to a AC3 file in real time, or a little slower. If I want to listen to my AC3 files and check they're OK, the new Soundblaster Live cards support AC3 as a surround format, so I can play back via one of those, via the digital out into a surround receiver like my Kenwood. That means I don't have to burn a DVD-R to check the file works."

Rik is doubly fortunate when it comes to mastering; most of his gaming clients will accept AC3 surround files as they are, so he usually has no need to take production any further and author his own DVDs. However, when this is asked of him, he does have access to DVD burners through Dolby, as well as hard-to-come by, expensive DVD-authoring software like MTC's Streamweaver. "If I'm giving the file to somebody else to incorporate into a project, such as a game, I simply burn an ordinary CD-R with the AC3 files on it. If I have to burn DVD-Rs, I'll use software like Streamweaver and burn them as a video DVD with audio only — the video stream remains blank". In this way, Rik can produce 5.1 surround-compatible audio from initial idea to finished DVD.

Surround Case Study 2: Abbey Road Studios

Our second interviewee this month is also intimately involved with the production of 5.1 audio from the recording stage through to DVD-compatible mixes, but at a very different level. Peter Cobbin is Senior Recording Engineer at Abbey Road Studios, London, and has been responsible for the production of many 5.1 mixes, originally to accompany music videos and films (such as The Beatles' 5.1 soundtrack for the re-released Yellow Submarine film, and surround soundtracks for DVDs of live concerts by the likes of Freddie Mercury and Eurythmics. More recently, he has been doing audio-only mixes to accompany DVD‑Audio releases. As he explains, "One of the reasons I love working at Abbey Road is that we have had a firm commitment to surround on the pop side since 1996, when I did Yellow Submarine. Every control room we have here is now capable of surround work, even the small control room in Studio 2."

Abbey Road Studio's 5.1-equipped mastering studio.Abbey Road Studio's 5.1-equipped mastering studio.We spoke to Peter in the famous Studio 3 at Abbey Road. As befits a world-class facility, the control room offers various ways of creating surround mixes; following a recent refit, it's now kitted out with a SSL J-series console, custom-modified to make surround mixing in the analogue domain easier. There are also numerous Pro Tools systems for tracking and mixing in the digital domain, complete with various multi-channel A-D/D-A units, an impressive B&W 801N surround monitor array, and a choice of possible mastering recorders, including eight-track Tascam DA98HRs and Genex magneto-optical recorders. There are even options at the very beginning of the recording chain, Peter having experimented extensively with Surround mics and mic arrays when making classical recordings destined for 5.1 presentation.

"We have a Soundfield mic, and that has worked well on some occasions. I have also done some recordings in Studio 1 with the Royal Philharmonic Orchestra, using a variation on the Decca Tree concept with Neumann M50s in an arrangement I call a five-way tree, which provides a 5.0 output with each mic effectively feeding its own speaker. For the best results, I reconfigured the orchestra from a traditional layout, so that it was ranged much further around the mic array than around a stereo mic array. It worked very well on this particular project, although it wouldn't suit everything. It wasn't a case of adding some rear-channel mics for ambience — I was trying to push things, to see what it sounded like with the orchestra enveloping the listener to a much greater degree than would normally be the case. I did have to spend ages setting up the mics relative to one another to minimise phase problems, though; I usually rig speakers out on the studio floor as a point sources to try out that kind of thing — that's a good test."

Peter started mixing for surround in the early days of the 5.1 format, in the mid-'90s, when there was very little custom-designed gear around. As such, he knows a lot about having to 'kludge' surround mixes with stereo equipment. Decent multi-channel converters, for example, are crucial to surround mixing, both at the tracking stage, where Peter is often bringing old material from analogue multitrack master tapes into the digital domain for 5.1 remixing, and also at the monitoring stage, where a digital six-channel mix has to be converted back to analogue to drive the monitors. "We use Prism eight-channel converters now, but when I started, there weren't any multi-channel converters, and I had to go around the building scrounging spare stereo converters to provide enough channels. I can remember once I had a Prism doing the Left and Right channels and a Genesis converter doing the Centre. I folded the front three channels down and it sounded horrible! It was the minuscule differences between the two converters — delays of just a few samples — that were causing the problem. You really have to have identical, phase-accurate converters for all the channels."

Mixing is taken care of in the analogue domain by the advanced routing of Studio 3's modified SSL J-series, or by Digidesign Pro Tools systems for digital projects. "We use Pro Tools a lot — I can't remember the last time I did a job without it in some capacity or other, either as a multitrack recorder, or in sync with my master recorders to do some fine tweaking, or as a machine to mix on to. Digidesign's own 888 interfaces have their limitations, but we generally bypass those with Prism converters. We record a lot of film scores straight onto Pro Tools, now that we can use the Prisms to provide the high-end quality. These kinds of software solutions often handle surround more comprehensively than hardware as well, even in relatively low-cost facilities."

With all these options on offer, you'd expect Peter to use only the finest true-surround effects units in his mixes, but perhaps in a hangover from his 'kludging' days, he has stuck mainly with pairs of stereo processors. "I am yet to commit myself to any multi-channel boxes, like the TC System 6000. My appraisal of the System 6000 was that I generally liked it, but it didn't give me the kind of flexibility and options in six-channel mode that I wanted. Since I was coping with two-channel boxes, I stuck with them. I love Prism EQs, and valve compression is still a favourite — particularly Chiswick Reach and Manley gear. We also have a number of TC M5000s which I have used for digital dynamics occasionally.

"Using two-channel dynamics processors for a surround mix can be tricky. It depends on how you are using the front three channels; you don't always want a six-channel compressor. If I have a vocal on the Centre channel and a drums and bass thing going on Left and Right, I will use separate compressors, because I want separate control. I don't find multi-channel dynamic processing essential. I can do what I need to with stereo boxes and more routing spaghetti in the patchbay here!

"When it comes to reverb, it's the same. We do have the Sony DRE 777, which is surround-capable, and I've used the Lexicon 960L. But at the moment, I prefer to have lots of discrete stereo reverbs, both digital ones and plates. I also like to mike up Studio 2's echo chamber and Studio 1. I'll often have as many as 12 reverbs running at once, which is why I need such a big desk. Sometimes I'll use a stereo reverb, but pan it off in a direction to create depth for an instrument."

Unsurprisingly, Abbey Road does not skimp when it comes to monitoring. Not only are the Audient ASP10 surround monitor controllers in evidence in all the surround-capable mixing studios, thus circumnavigating the level control problem, there are impressive arrays of surround monitors too, as Peter explains. "I scouted around for decent full-range speakers for Studio 3 that could handle pop and classical work when I was about to start Yellow Submarine, and that's when B&W made the first prototypes of these 801Ns. They've gone on to be a tremendous commercial success. Some of the mastering rooms have B&W 802Ns and others have the 801Ns. The small control room in Studio 2 has active KRKs, and there are domestic surround systems in the lounges — there must be at least a dozen surround monitoring systems in the building. Having a variety of different surround monitoring systems, both professional and consumer, is important, just as it is with stereo mixing — I have five different stereo monitoring systems in this control room to check mixes."

Surround master recording hardware has also come a long way since Peter began surround mixing. "When I started, the only real multi-channel master recording option was the DA88 with Prism converters, bit-splitting to give six channels at 20-bit resolution. We now have the Genex magneto-opticals and Tascam DA98HRs, which both give 24-bit resolution over eight tracks. Some of our classical guys reckon the Tascam converters are fantastic and have stopped using the traditional external A-D interfaces!"

Once Peter has completed his six-channel mixes, they are sent elsewhere in Abbey Road for mastering and DVD authoring (all of which is handled in house). There'll be more from Peter's colleagues who handle that side of things in next month's instalment of this series; suffice it to say for now that DVD metatag creation and disc authoring takes place on high-end SADiE and Sonic Solutions systems well beyond the budget of most home studios.

In Part 7

In Part 7 of this series, I'll be looking at some of the things that can be done with surround at the mixing stage, as well as pointing out potential pitfalls, and we'll hear again from Rik and Peter about how they deal with the various difficulties in their very different recording setups.

Surround Sound Explained: Part 1 Foundations

Surround Sound Explained: Part 2 Dolby Pro Logic

Surround Sound Explained: Part 3 Ambisonics

Surround Sound Explained: Part 4 5.1 Surround

Surround Sound Explained: Part 5 Metadata, Upmixing, Downmixing & The Centre Speaker

Surround Sound Explained: Part 6 Setting Up A Surround Recording System

Surround Sound Explained: Part 7 Mixing In Surround

Surround Sound Explained: Part 8 Surround Production

Surround Sound Explained: Part 9 Surround In Your DAW

Published January 2002