Studio SOS: Monitoring

The untreated studio...

Dave Rogers was having trouble with his monitoring, so the SOS team sped over to his home studio in Bristol, England, to sort things out.

Dave had improvised speaker stands using piles of concrete building blocks. However, his original design (above) was rather unstable, so Paul rearranged it into this more stable configuration, and added some Auralex Mo Pad foam isolation pads for good measure.Dave Rogers left his native Boston on the east coast of the USA to live in Bristol, where he has set up a home studio in a small room created by partitioning off the last eight feet of his single garage. This has left him with a near-cuboid space measuring approximately eight by eight by nine feet, where three of the walls are solid and one is a studding 'drywall' partition incorporating a doorway to the rest of the garage. A side door in one of the solid walls provides access.

Dave's recording system is based around a Mac Powerbook laptop fitted with 1GB of RAM and connected to the outside world via an M-Audio Firewire 410 audio interface that provides one set of MIDI ports. The active monitors are also from M-Audio (BX8s) and Dave had these set up on piles of heavy concrete building blocks, a cheap alternative to speaker stands which Paul suggested to him on the phone while arranging the visit. He also has a Novation rackmount synth, a Micro Korg synth and a couple of processor boxes, including a Dbx 266XL compressor, which he had connected to the aux send and returns of the small Behringer Eurorack MX2004A mixer he was using to feed his synths into the audio interface.

When we arrived, the room was completely untreated, so the acoustic was predictably boxy and ringy, given that there was only the floor covering and the equipment in the room to absorb and scatter the sound energy. We played some commercial tracks over the speakers, and were greeted by a very confused sound with exaggerated presence and high end, no real stereo imaging, and a lot of overhang on the bass notes. As is common with small rooms, the bass end dipped considerably if you listened from the dead centre of the room, which is where Dave's chair normally sat. He'd noticed something was wrong, because his headphone mix always seemed to have a lot more going on at the low end than appeared in his monitors.

As usual, we started by trying to optimise the monitoring system prior to treating the room, and it was immediately obvious that the stacked concrete blocks were far from rigid, so we dismantled them and built them up again as shown in the photograph, with two blocks one way, then two the other, capped off with flat blocks on top to form a platform. This was far more rigid, and once we'd added a pair of Auralex's dense foam Mo Pads the speakers were at the correct height with the tweeters pointing directly at Dave's head when he was seated in his monitoring chair.

Hugh switched off the mid-range boost setting on the M-Audio active monitors, and also tamed their over-prominent high-end response by reducing the tweeter level a little.

Hugh then checked the EQ settings on the backs of the speakers, which were set flat except for the mid-range presence switch. He turned this off and also dropped the tweeter level by 2dB, as one characteristic of these speakers seems to be an over-pronounced high end. He also reduced the bass extension from the lowest 37Hz setting to 47Hz, which initially seemed more appropriate for the small room.

Rewiring & Reorganisation

The result was a slight improvement, but at this stage the room acoustics were still playing havoc with the monitoring. We also noticed that every time David needed to replay anything he had to do a lot of re-patching, so we suggested reorganising his system slightly before proceeding with the acoustic treatment. With small systems such as this, a simple option is to feed the stereo output from the audio interface into the two-track returns on the mixer and then select this two-track return as the mixer's monitoring source. The advantage of this approach is that the mixer's control room monitor level control can be used to adjust the monitors, whereas previously Dave had fed the monitors directly from the output of his audio interface, which meant that he had to adjust the playback volumes in software. The input channels could then be mixed as normal and fed to the audio interface inputs via the mixer's main stereo output.

Dave has his synths connected to the mixer, but he also has a DJ deck setup that could be fed into the mixer for monitoring or recording purposes. For playback or keyboard playing without the computer, the mixer could be switched back to monitoring the main stereo mix rather than the two-track input. We rewired as above using Dave's existing cables, all of which were unbalanced. There was little hum or noise in evidence, but using balanced cables to feed the active M-Audio monitors would have been better. The two-track inputs were on unbalanced phonos anyway, so the existing cables were fine.

Dave had been monitoring his mixes directly from his audio interface output, but this meant that he needed to re-patch to play anything else back over his studio monitors. By rewiring the audio interface outputs to the mixer's two-track inputs instead, Hugh was able to set up much more flexible monitoring, making better use of the mixer's routing facilities.

Next we explained that compressors aren't normally used in effects send-return loops unless you're doing certain unconventional mastering tricks, and as Dave was using Logic Pro 7 on his laptop he could always compress within the software using Logic 's included plug-ins. However, he liked the sound of the Dbx on certain bass-synth sounds, so Paul suggested that he hard-wire the Dbx compressor between his Novation synth (which is the one he usually uses for bass) and the mixer input.

One odd occurrence Dave demonstrated to us was that whenever he booted up the computer, the stereo image was obviously offset to one side. This turned out to be due to Audio MIDI Setup in the Mac OS turning down one channel by 2-3dB for no apparent reason. Dave had even gone so far as to completely reinstall the OS, but the problem still remained, and he tells us that it only started after he installed the M-Audio Firewire 410. Until a solution is found, he has to go into Audio MIDI Setup and reset the faders every time he starts up the computer.

Control Room Bass Problems

After an eclectic lunch of chocolate Hobnobs augmented by real chip-shop fish and chips, we turned our attention to the sound of the room itself. Being realistic, a small room like the one Dave has is never going to make an ideal monitoring environment, but we felt that it should at least allow mixes to be created that don't sound too far out of balance when played on other systems. As we knew we were going to face bass-end problems in such a small room (the smaller the room, the more widely spaced the room modes, and the less even the bass will be), we brought along a couple of Mini Traps kindly donated by Ethan Winer of Real Traps. Ideally you'd need four or more of these traps to really make a serious dent in the problem, but Dave agreed that if he could hear an improvement with two fitted, he'd buy two more to fit himself at a later date.

Fitting the Real Traps bass traps was a simple matter of fixing nylon cord through the holes on the back of each trap's metal frame, and then hanging the traps from hooks which had been screwed through the plasterboard into the ceiling joists.

Mini Traps work on a different principle to the acoustic foam panels that Auralex normally provide for our Studio SOS visits: acoustic foam absorbs sound by frictional loss, and its effectiveness at low frequencies is directly related to its thickness and its spacing from the wall. On the other hand, the Mini Traps use the principle of lightweight panels between which are sandwiched three inches of damping material. These traps are then fitted across corners (usually between walls and ceilings), the idea being that the bass energy tries to move the panels and the damping material behind absorbs the energy rather than reflecting it back into the room.

The easiest way to hang these panels is by using picture-frame wire or nylon cord, and we used the latter for simplicity. However, getting the cord length right to get the panels hanging correctly proved to be quite tricky. We also had to locate the ceiling joists to screw in the hooks needed to support the cord. However, once the panels were up, they looked fine and seemed stable. Another listening test showed that the bass dip in the centre of the room was noticeably less fierce and the bass notes didn't appear to overhang as much. Equally importantly, the levels of bass notes were now more even, though still not perfect. Two further traps would improve this situation, but as it was, the bass performance of the room seemed adequate, provided that any crucial monitoring decisions were made with the chair pushed back behind the centre of the room.

Acoustic Treatment

In order to tidy up the monitoring system's stereo imaging, Paul and Dave used contact adhesive to glue acoustic foam panels around the side walls of the room, thereby reducing acoustic reflections reaching the mixing position.Next we used four panels of Auralex foam to tame the remaining ringing and boxiness, following the usual strategy of placing absorbers at each side of the listening position to damp side-to-side reflections — these are the ones that have the most detrimental effect on stereo imaging. A further panel was placed on the rear wall to reduce reflections from that surface, and the remaining panel was cut in two and glued to the wall behind the monitors. Ideally we'd also have placed a panel on the ceiling centred just forward of the monitoring position, but we didn't have enough material with us to do this. Dave said that he'd buy a panel as soon as possible and fix this himself.

A spirit-level helps with optimal positioning of the Auralex treatment.

Once the acoustic foam was in place, the difference was immediately obvious. Just speaking in the room showed that it was much better damped, and all that 'broom cupboard' boxiness was gone. Playing the same material over the monitors confirmed that everything now sounded less confused, more controlled, and tighter, with greatly improved imaging. There was still some bass drop-off at the exact centre of the room, but nothing as bad as what we'd heard before putting up the Mini Traps. The consistency of level across different bass notes was also better. Dave seemed very pleased with the sonic improvements, and also with the ergonomic benefits of rewiring the mixer to allow it to control the monitor level.

During the day, we'd tried using the monitors set to a higher bass roll-off position, but with all the treatment work complete, we found we got a better correlation between the monitor mix and the headphone mix if we set the speakers back to their full bass extension. We stuck with the flat mid-range setting and the 2dB high cut, and left the environment switch set for half-space operation, which is usually best when the speakers are used close to a wall. For judging mixes, it would still be better to roll the seat backwards a foot or so away from the dead centre of the room, but that's easy enough.

Sequencer Tips

We used up our remaining time going through a few Logic tricks with Dave. He's a big fan of synth bass sounds, so we tried processing some of his patches using Logic 's Guitar Amp Pro and Phase Distortion plug-ins, which Paul has found to be very effective in getting dirty Leftfield-type heavy bass sounds. The guitar amp can produce more subtle effects, and by choosing the right speaker-cabinet simulation it's often possible to create more analogue-like sounds. Not only does this sound good, but it also tames the high-frequency harmonics in the sound, so it's often easier to place the bass line in the mix without it trampling all over the mid-range. Paul also demonstrated using Logic 's Tremolo plug-in as a beat-sync'ed chopper for turning pads or other sustained sounds into rhythmically supportive elements.

To wrap things up, Paul demonstrated how Dave could make Logic quicker to use by spending some time setting up a suitable default project, with all the MIDI routing, audio tracks, and mixer channels he might need.

Dave was fairly new to Logic, so we also covered a couple of basic operation tips, the first and most obvious being to spend the time to create a comprehensive default Song with Screensets arranged to navigate quickly between the most commonly used screens, such as the Arrange window, the Track Mixer, and the Environment. The use of Screensets is particularly important when using a laptop, because of the very limited screen space. However, Screensets are saved with each Song, so you need to work them into your default Song if you want them to appear in new Songs you create.

Another great space-saver for laptop users is to use the Arrange window's View Channel Strip Only key command, so that you can easily toggle between seeing the whole channel strip on the left of the window or all the parameter windows plus just a part of the channel strip.

Our final tip was to use the Escape key to bring up the toolbox at the current cursor position, as this saves having to move over to the left of the screen every time you wish to select a new tool. Hitting Escape a further couple of times brings you back to the original tool. Paul also recommended Dave get the version 7.1 upgrade, as it includes a few further improvements. Upgrading Mac OS to Tiger would probably also be a good move as well in his experience, as Logic is much more stable under Tiger than under the previous versions of Mac OS X.

Before we left, Dave asked our advice on improving the entrance door. As daylight was clearly visible around the edge, and it was a lightweight door, it leaked quite a lot of sound. We suggested adding a layer of half-inch plywood to the inside, with Rockwool filling any spaces, then fitting a compression latch to pull the door hard against the frame when closed. The door frame could then be modified with neoprene foam seals that touch the door on all four sides to make it airtight. While a single door will never be as good as two spaced doors for isolating sound, the difference should be very worthwhile. It may also be worth damping the door leading through to the garage, as the light pine panels may resonate when hit with high levels of bass.