Acoustics & Technique for a Better Studio
We’ve recently covered the acoustic issues that concern control room monitoring, but are things any different for recording rooms? Huw Price investigates live and dead rooms, the creative use of room acoustics and old-school tricks with gobos...
Serious recordists tend to obsess about stuff. We’ll pick over the minutiae of a classic drum sound, a landmark guitar tone or a particularly fine vocal recording. We may search online to discover which microphones, preamps or compressors were used for a particular recording, or even get totally hung up on cables or electronic components. Checking out recording forums, it’s not uncommon to find contributors squabbling over all manner of technical inconsequentialities.
But the one factor that always seems to be missing from these discussions is the acoustic environment in which great recordings were made. There’s no getting away from it: every time you use a microphone you have to deal with room acoustics, and the sound of a room can have a more profound influence on the final outcome of the recording than any other factor. For instance, let’s assume you have a pair of bright-sounding omnidirectional condenser microphones and they have always sounded great as drum overheads in your dry and slightly dark-sounding recording room. Then, one day, you’re asked to record drums somewhere different, in a room with a concrete floor, lots of flat reflective walls and plenty of windows.
A room like that will sound extremely bright and ambient and the upper frequency lift of your mics might make cymbals sound clangy, harsh and edgy. The mics and your signal chain are exactly the same, so what can you do?
The first thing not to do is panic. If you have a basic understanding of room acoustics, microphone positioning and pickup patterns as well as acoustic treatment, you can still get the sounds you want. In fact, overcoming fears about exploiting room acoustics can open up a world of creative opportunities. Gear selection, obviously, will always be important, but if you factor in a degree of acoustic awareness, you may find that your recordings will become more individual, characterful and interesting.
Room acoustics
For our purposes let’s define the opposite extremes of room acoustics as ‘wet’ and ‘dry’. Reverb is actually formed by multiple echoes that are so close together they appear to sound continuous. When a room is very ‘reverby’, we’d describe it as ‘wet’ and you may have experienced reverberant environments in large areas such as stairwells, churches, cathedrals and big empty halls.
When there is no absorptive material, the soundwaves will continue to bounce around for quite a while, so we’d describe this a long reverb time. If some absorptive material is present, like carpet or curtains, the reflective soundwaves will be soaked up more quickly.
As long as there are some reflective surfaces, the room will retain a degree of reverb, but we’d describe shorter reverb times as ambience. If you’ve ever gutted a room for decorating then gradually re-introduced carpet, curtains and soft furnishings, you’ll understand how the acoustic ambience of a room can change.
Completely non-reverberant spaces are called anechoic chambers and are really only useful for measuring loudspeakers, microphone responses and so forth. However, heavily furnished rooms can sound quite dry and if any your cupboards are large enough, try recording in there for a seriously dry sound. The late Fad Gadget recorded all his early work in his airing cupboard and Mickie Most often put Jeff Beck’s amp in a wardrobe.
Acoustic trends
Many of the earliest pop and rock recordings were made in studios that had already been around for decades and were originally designed to accommodate orchestras. Listen to the recordings The Beatles made at Abbey Road and you can hear that they weren’t made in small, dead rooms. Or check out Jean-Luc Godard’s film Sympathy For The Devil to watch The Stones recording at Olympic. Could you even imagine putting Jimi Hendrix’s rig in a vocal booth? He’d probably have ‘blown the bloody doors off’. Room acoustics and spillage had a huge impact on recordings from the 50s and 60s.
Contrast that natural and airy quality with many recordings from the 1970s. The studio scene had evolved and the role of the new breed of engineer/producer had moved beyond technician/project manager to become something more akin that of a film director. There was a growing realisation that the studios themselves could be ‘musical instruments’, and in order to realise the full potential (and establish complete control) of all those groovy effects, extraneous things such as room acoustics needed to be eradicated.
Studio live rooms became ‘dead’ environments and drums were often recorded in ‘booths’ lined with copious quantities of absorbent materials. Think of the thuddy, dry-as-dust drums on Dark Side Of The Moon (Pink Floyd) or just about any disco/funk track.
These sounds were also great, but they were just different. However, some bands, like Led Zeppelin, bucked the trend and made heavy use of ambience mics while recording tracks like When The Levee Breaks in large country houses. Many of the earliest punk recordings also had more of a ‘live’ sound that better suited the raw energy of the genre.
Although guitar and vocal recordings mostly remained dry, 80s producers like Steve Lillywhite started getting into ‘big drums’. Big drums meant big rooms with lots of microphones to capture all the ambience. Remember: those were the days when most records were done on 24-track tape and it wasn’t uncommon for 12 or more of those tracks to be dedicated to the drums alone.
Technological advances had provided producers with the tools to manipulate and process the drum sounds. For instance, they could apply such extreme compression to the ambience it would almost flip backwards. Gates could also be applied to ambience tracks and triggered from the close microphones. Prime examples include Robert Palmer with The Power Station and Phil Collins’ In The Air Tonight.
Many of those 80s drum sounds were achieved in rooms that were lined with stone, which gave the sound added brightness. Things were made even brighter by powerful desk equalisation and Aphex Aural Exciters (combined with an ear-numbing vogue for cocaine).
Whether by design or accident, many of us find ourselves recording in dry spaces once again. Old-style studios with large live areas are now comparatively scarce and expensive. Many commercial recordings are made in programming rooms with small, acoustically dry recording rooms, and you may even find artists and engineers working in the same room. Those who are serious about acoustic recording are often obliged to find locations with suitable acoustics where they can work. Many of us keep our gear permanently flightcased to make dismantling and reconstructing our studios easier when we have location work. Popular makeshift studio locations may include village halls, churches or large country houses (depending on your budget, of course!).
Ambience and spill
We’ve established that recording musicians individually and together in ambient spaces can produce some amazing sounds, but it does present some technical challenges. Principally, these include unwanted ambience and spillage – whereby sound from instruments leaks into the ‘wrong’ microphones. As these are both issues that every recordist will have to deal with at some point, let’s look at controlling ambience first.
DIY acoustic control is now well established in the home recording sector and it’s invariably applied to rooms in which accurate monitoring is the first priority. Of course, all the same acoustic phenomena applies to control rooms and live rooms, but while we generally seek to neutralise the frequency response and reverberation of a mixing/monitoring room, those same characteristics can actually be desirable in a recording space.
Control room acoustic treatment usually involves the permanent installation of absorbers and diffusers of some description. The same techniques can also be applied to recording rooms, but it’s preferable to be able to add acoustic control only when and where it’s needed. Different instruments and production techniques require varying amounts of acoustic ambience, so most live-room acoustic treatment needs to be impermanent and portable if it is to be practical.
But is spill necessarily bad? There are various schools of thought on the issue, but from the inception of multitrack recording, engineers sought to control it. This was eventually taken to the extreme, with individual instruments often being recorded in complete isolation – at which point, some daring souls began to wonder if having musicians playing together in a room might actually inspire better performances…
Some engineers take the view that spill can be ‘the glue that holds mixes together’. However, most would regard spill as desirable – or even acceptable – only so long as it isn’t excessive and doesn’t compromise the overall production values in any way. But many of the techniques for minimising acoustic ambience also apply to minimising mic spillage, so let’s take a broad view, starting with microphone techniques.
Microphone magic
Engineers can control and manipulate room acoustics through the selection and placement of microphones, much of which comes down to common sense. Try to stick to close-mic’ing whenever you want a dry sound with minimal spillage. Also consider how you can make pickup patterns work in your favour.
If you’ve got a ribbon microphone on a guitar amp, try aiming the ‘deaf’ side of the mic towards the drum kit. Remember that hypercardioid microphones, unlike regular cardioids, do pick up some sound from the rear, so avoid pointing the rear of a hypercardioid mic towards anything loud. Obviously, omnidirectional mics aren’t the best choice when you’re trying to minimise spill.
Some engineers swear by lavalier microphones – like the ones that clip onto the shirts or jackets of TV presenters. Try slipping one through the vent hole of a snare drum or tom in place of an ‘underneath’ mic. Also investigate stick-on miniature condensers, like the DPA SMK4061, on acoustic guitar. They’re very good on grand piano, too, because you can attach them to the inside lid then close it and cover the piano with duvets or blankets. PZM mics can also be stuck to piano lids with gaffer tape.
Don’t be afraid to use bass roll-off switches. If there’s a load of kick drum or electric bass ambience flying around the room, high-pass filter switches can remove some low-frequency content and shouldn’t affect higher-pitched instruments too much.
Companies like Auralex produce absorbent foam collars that provide a bit more isolation for microphones. If you’re on a budget, try cutting a mic-size hole in a square of foam and pushing a microphone through it. If you’re using a cardioid mic, be careful not to cover the rear of the grille area with foam because this will turn it into an omni mic and make matters worse.
Room to manoeuvre
Sound engineers have always used whatever comes to hand, and this particularly applies to controlling ambience and spill. Although there are plenty of specialised products on the market, room acoustics and microphone isolation can be dramatically improved using household items such as duvets, sleeping bags, blankets and cushions.
For instance, it’s very common to build a bass drum tunnel using any of the above items to isolate the kick drum mic from other sounds in the room. Throwing a blanket or duvet over a guitar or bass cab can also work wonders if you’re aiming for a dry sound. Just make sure that you’re not blocking any air vents, otherwise you could start a fire…
If the room is generally too live, try scattering some rugs or carpet pieces over the floor and drawing curtains or blinds across any windows. If there’s too much bass build-up, leave the door open to let some of those soundwaves escape. Remember that anything goes, and whatever you use doesn’t necessarily need a brand name stamped on it to achieve professional results.
On the gobo
Gobo is a US studio term for movable, free-standing acoustic panels or baffles that are used to achieve extra separation in studio recording situations. They can also be used to alter acoustics in the vicinity of a microphone and commercially made gobos often have a reflective side and an absorptive side to liven up or deaden the sound respectively.
Ideally, a gobo should go all the way down to the floor; if there’s a gap at the bottom you won’t notice much improvement in separation. Even with well-designed gobos, the best you can hope for is a reduction in direct sound spill because gobos aren’t particularly good for dealing with ambient spill.
If you’re looking to buy some gobos there are plenty of manufacturers out there making them. The advantages of buying professionally made gobos are that absorption should be fairly even across the frequency range and they will look good. Some control room absorbers are also designed for stand-mounting, so when you’re recording you can take them into your live room then replace them come mix time.
Home recording enthusiasts may be interested to learn that gobos are actually quite cheap and easy to make and there are plenty of online sources that can tell you how to do it. Alternatively, look out for acoustic screens from second-hand office equipment dealers. So, how can gobos be useful?
Memphis-based producer and engineer Jeff Powell learned a trick or two about setting up bands together in a room from the legendary Glyn Johns: “We were recording bass and guitars in the same room as the drums, so he had me put tall screens on each side of the kit then we put the bass amp on the left and all the guitar amps on the right, with screens placed between each one. He said the key to this was getting the bass cabinet parallel with the outer kick drum head. I’ve done it and it’s like they’re playing in booths – the spill is inconsequential. If you get that going on and isolate the singer it sounds like an old Stones record. The only time it doesn’t work is when the band starts getting into volume wars!”
Splendid isolation
Although it seems counter-intuitive, you’ll achieve better separation between two guitar amps by placing them right next to each other rather than at different ends of a room. Bring the sides of the cabinets right up next to each other so the fronts are lined up and firing in the same direction. Then place a gobo between them – or even some cushions from a sofa – and close-mic each cabinet in cardioid.
The close-mics will pick up almost no direct sound from the other amp and since they’re placed right up against the speaker, the direct sound will be much louder than any ambient sound that’s floating around in the room. The degree of separation will probably amaze you.
If you’re recording bass at the same time, arrange all three amps in the same way, with the bass amp in the centre. If you’re recording drums, too, try arranging screens in front of the drums and place any amps right in front of the screens. If the cabs are open-backed, push the backs up against the screens to minimise rear radiation.
Soundwaves can build up in corners and the junctions between walls and floors to create a low-frequency lift. Some engineers like to place gobos across any corners in a room to nullify this effect. You can achieve similar results by propping up mattresses. However, some engineers use gobos specifically to create corners – Jeff Powell, again: “I’ll often take a couple of baffles and arrange them in a ‘V’ shape pointing at the kit, maybe ten feet away. I’ll put a decent-size tube condenser into the ‘V’ somewhere near the floor then compress the hell out of it. The baffles help to keep some of the cymbals out so they don’t control the dynamics of the compressor too much. It gives that John Bonham power thing if you just mix in a bit with the rest of the kit mics.”
British rock and metal producer Chris Tsangarides is famous for his ‘vortex method of recording guitars, as he explains: “I was a tape op at Morgan Studio and I was left to record a guitar solo when everybody else went down the pub. The band was Phil Collins’ side project, Brand X, so there I was with the guitarist, John Goodsall, and I thought, ‘how can I make this guitar really loud?’.”
We had these huge screens so I decided to build a whopping great bass bin to channel the sound. We ended up with a couple of walls that were 30-feet per side, like a ‘V’ formation coming off the stack. So I put mics up everywhere and started panning the ambient mics around on the quadraphonic desk we had. After I while I stopped panning but the guitar sound carried on moving. It was like, ‘what the hell is going on?’.
“I soon figured out that I didn’t need all those mics. I find a spot in the room where I like what I hear, then I put the room microphone where my head is. I liked the principle of having the close-mic on one side of the mix and the room mic on the other. Then, when I double-track, I reverse the panning so that the close-mic and the ambient mics are the opposite way around on the second take. You get a wall of guitar but with a distinguishable left and right.”
Although the usefulness of gobos for reducing spill is limited, they can be pretty effective for reducing room ambience. For instance, surrounding a drum kit with absorptive gobos can help tame excessive roominess. You can also arrange them in a square to create a ‘booth’ for vocalists – sometimes with packing blankets or a duvet spread over the top for a ‘roof’. As well as keeping the room sound away from the vocal, many singers enjoy the intimate and private space this creates.
Sound proof
Much of what we’ve covered here is just old-school sound engineering. Although there are some amazing products out there for controlling spill and ambience, you can still achieve incredible results using regular household objects, ingenuity and a bit of technical nouse.
This feature first appeared in Music Tech Magazine issue 96
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