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Studio SOS: The Cave

Paul and Hugh head off to The Cave!
Published January 2015
By Hugh Robjohns & Paul White

Before the visit. The monitors were set up to fire down the length of the room, as is usually recommended, but their configuration on the table was suboptimal.Before the visit. The monitors were set up to fire down the length of the room, as is usually recommended, but their configuration on the table was suboptimal.

Team SOS travel to deepest, darkest Cornwall, where they encounter some troublesome low frequencies and tackle a few common mix quandaries.

Located in a small industrial unit just outside St Austell in Cornwall, The Cave studio is owned and run by Beren Matthews and singer Louella Jade Eke, who took over the building from a previous studio operator. They subsidise the studio by hiring out the performance area as a rehearsal space, but Beren’s aim is to get the control room up to the standard that it could be used for community music projects, as well as for his own band.

When he took over the property, the control room was a simple, plasterboard–on–studding construction with a large vocal booth built into the rear corner. There was no adequate acoustic treatment in the room or in the vocal booth, so when Beren first called us for advice we suggested he remove the booth to give him more space and then build some mineral wool traps to hang on the walls and across the corners to try to tame the acoustics. He built some wooden frames to accommodate medium–density Rockwool slabs of 30 and 50 mm thickness, and then covered them with a purple fabric. Four were placed across the corners, but didn’t fit tightly against the walls because they jammed between the ceiling and floor, leaving significant gaps either side. The rest were hung on the walls or propped up on boxes.

Speakers Of The House

After a long drive, Hugh and I arrived with our bag of tricks, and over the ensuing coffee and oaty biscuits Beren outlined the issues he saw as being most serious. Primarily, despite all the broadband absorber panels, the monitoring still didn’t sound right, and there was also the issue of positioning Beren’s Adam A7 monitors and Yamaha NS10s on the small desk to allow both to produce decent stereo imaging. As Beren had his monitors set up, the Adams were very close together and so didn’t produce such an impressive stereo image as the NS10s. The power amp used to drive the NS10s also produced quite a lot of physical noise, due to its cooling fans. Hugh suggested that this might be relocated to the void between the control room and performance area — a potential mini-machine–room space!

We experimented with different mounting arrangements for the NS10s and Adam A7s, to try to improve the stereo image, but the more we experimented the more we became aware of much more fundamental room acoustic issues — so our first job was to listen to the room and run a few test signals to see how it was behaving. Beren was using a subwoofer with his Adam monitors and had already moved it to where it seemed to be giving the most even results, but there were still some very obvious bumps and dips in the room’s response.

The Low Down

We had intended to start with a test tone sequence run from Hugh’s test CD, but it turned out that Beren had upgraded his iMac to include an SSD drive, which had necessitated removing the CD–ROM/DVD drive. He also had no Internet connection at the studio. Undeterred, we created a semitone staircase of tones using the EXS24 sampler that comes with Logic Pro X, his DAW of choice. If you don’t load any samples it plays a default sine wave, and with all the notes set to the same velocity, the test quickly revealed some serious dips and peaks in the 120 to 220 Hz range — though the deep bass didn’t seem too badly behaved. The frequencies of the problematic standing waves suggested issues related to the height and width of the room, rather than its length.

Supervillain Paul White scrutinises different monitor arrangements while listening to a  sine–wave test set up in Logic Pro X.Supervillain Paul White scrutinises different monitor arrangements while listening to a sine–wave test set up in Logic Pro X.Our first thought was to try to move the speakers and desk relative to the front wall, and though this caused some small changes in the shape of the response, we got no closer to ironing out the bumps. We also turned the sub off and ran the Adams full range to avoid having too many issues in play at the same time, but still we found the same problems. Beren’s monitors were already set up to aim down the length of the rectangular room, which was just under six metres, so we had to conclude that the problems were due both to room modes and, to some extent, resonances in the single–skin plasterboard walls. Given the inevitably limited budget, the best solution for the walls would be to add another layer of plasterboard fixed with Green Glue at a later date when the studio has generated some income. The additional layer would add mass, while the Green Glue would introduce some much–needed damping.

It’s A Trap!

However, we needed a more immediate solution, and after some head scratching we decided to try to improve the performance and effectiveness of the corner traps and existing panel traps. We started by placing the thicker panel traps at the mirror points, and spaced them a couple of inches from the walls to improve their low–frequency performance significantly. We achieved this using some of the timber left over from demolishing the vocal booth, screwing a piece of 50 x 100 mm studding behind the top of each frame with a smaller block cut from the same material at the bottom. A trip to the local DIY store produced the necessary screws and plasterboard fixings. The use of such substantial pieces of wood was not only because they were conveniently to hand — we also hoped they would help to brace and dampen the relatively flimsy plasterboard walls, too, reducing their propensity to resonate. After fixing the mirror–point panels we used the same technique to mount a number of thinner panels further back on the side walls, and on the rear wall above a sofa.

Turning to the corner bass traps, we had our doubts as to how effective they would be as they were simply thin Rockwool floor–to–ceiling panels wedged across the corners, leaving 100 to 150 mm gaps at each side. Rather than try to cut them down slightly so that they could be fitted tightly across the corners, which would have been quite a tricky and messy job, we asked Beren if he had any leftover mineral wool. He only had a few scraps but he did have a lot of insulation-grade fibreglass that he didn’t need, so we suggested he use it to fill as many plastic rubbish sacks as possible with a view to cramming them behind the existing corner trap panels. It wasn’t the prettiest of solutions, but we had enough to fill the front two corners and it turned out to be surprisingly effective. There is no need to use ‘breathable’ sacks in this application as low frequencies have no problem getting through thin plastic bags, and the loft insulation absorbs LF energy very well.

“It’s not what it looks like!” Hugh Robjohns doing nothing at all untoward to Beren Matthews’ subwoofer.“It’s not what it looks like!” Hugh Robjohns doing nothing at all untoward to Beren Matthews’ subwoofer.The final wall that we needed to treat was the one in front of the monitors, and Vicoustic had kindly provided a box of eight of their Cinema Round acoustic panels, each comprising a curved solid foam block covered in an attractive black velour-style fabric. We fixed these using spray adhesive in two rows of five and three (the smaller, lower row being necessary to accommodate a mains outlet), and they looked great. After treatment the room certainly sounded a little less live then before, but how about those bass problems?

On running the step–tone tests again we found that the problems were much diminished, with only a couple of small and broad dips, and a peak of 5 or 6 dB at 200Hz still in evidence. An EQ cut of around 5dB at the problem frequency gave us a much smoother and totally workable result, so after fine-tuning the EQ plug–in settings, we saved it as a preset to be used in Logic’s output bus when mixing — but with a reminder to bypass it when bouncing.

The front wall and mirror point absorbers improved the imaging precision, but if the two sets of speakers were positioned beside one another the outer set would always sound more spacious than the inner set. To get around this we put the Adam speakers at the desk’s edges to keep them well apart, and then used a couple of speaker stands that Beren had lying around to support the NS10s so that they were directly behind and above the Adams. Switching between the two sets of monitors now resulted in a consistent stereo image, making it much easier to make reliable balance judgements. Hugh made some final tweaks to the sub level setting and by this time Beren had managed to borrow a USB CD–ROM drive so that we could run Hugh’s test songs and tone steps to confirm that all was well. It surprised us how much tighter and more even the sound was, with good stereo imaging from both sets of speakers. We suggested that Beren should get hold of some more insulation to treat the rear corners — you can never have too much bass trapping — but for now the room was behaving well enough to work in.

Mix Fixes

We then turned our attention to some of Beren’s mixes in progress, which already sounded pretty good, though perhaps a little lacking at the low end and lower mid-range, possibly because the inaccurate monitoring had lead him to cut the lows more than necessary. He’d also got into the habit of using a lot of plug–ins on each source, often in combination, so we tried to come up with some alternatives that would put less of a load on the CPU of his iMac as well as avoiding the phasiness that can occur when several EQ plug–ins are cascaded.

The final configuration. The NS10s were placed on stands behind the Adam A7s, which allowed both sets of monitors to present a  good stereo image. Along the wall on the back can be seen the Vicoustic Cinema Round panels, and hiding behind the corner traps are sacks of insulation, to help bolster the bass traps’ performance.The final configuration. The NS10s were placed on stands behind the Adam A7s, which allowed both sets of monitors to present a good stereo image. Along the wall on the back can be seen the Vicoustic Cinema Round panels, and hiding behind the corner traps are sacks of insulation, to help bolster the bass traps’ performance.The kick drum in one of Beren’s mixes lacked any real weight, so we tried Logic’s sub–bass generator combined with EQ to cut the extreme lows below 40Hz but to add boost in the 90Hz region, followed by more cut at 150 to 180 Hz to avoid boxiness. We also demonstrated how an Exciter–type plug–in could accentuate the beater click of the kick drum, as well as being useful for adding life to dull snare drums or overhead tracks where the cymbals aren’t cutting through.

Next we tweaked the bass guitar track to give it more punch, and the trick Beren liked the most was using Logic’s basic Limiter plug–in with the soft–knee box ticked to add attitude to both vocals and drums. It makes a useful alternative to a compressor when you need something a little more hard–hitting. For the electric guitars, we demonstrated the tonal variety that could be achieved by ‘re–amping’ the parts via a plug–in amp and speaker emulation, as an alternative to using EQ and compression.

Driving Theory

While we were at it we also showed how a simple overdrive plug–in can be used to add a tube–like warmth to sounds such as bass, drums or even vocals, as long as you keep the amount of drive fairly low so as not to give the game away. Next came some of our vocal processing tricks. Beren had used various plug–ins to brighten the vocal sound, but as an alternative we simply used some shelving EQ lift at around 7kHz combined with 80Hz low cut and the aforementioned limiter. We then went on to demo some of our double-tracking tricks, specifically using reverb early reflections (with no reverb tail) delayed by 50 to 90 ms to create a diffused slap–back sound.

Beren also explained that he’d been having some problems when using a compressor for level ducking, as the amount of gain reduction varies depending on the level of the side–chain input. I showed him an alternative method using Logic’s gate instead of a compressor, where setting the gain reduction slider to actually increase the gain by a few dBs when the gate is ‘closed’ allows a precise amount of gain reduction to be set. Essentially the signal is always boosted by the amount you set on the slider, except when a side–chain signal is detected, at which point the gate opens and the gain falls back to unity. The attack and release controls vary how quickly the ducking comes in and out.

Easy As ADT

Beren had also bought the Waves Real ADT plug–in, which is actually really good, but again we showed him one of our favourite alternatives that requires a copy of the original track to be delayed and then subjected to pitch correction using something like Autotune or one of its many imitators — in this case Logic’s own Pitch Correct plug–in. When played back alongside the original part, the pitch-correction plug–in provides the necessary pitch variation, while the delay produces the required doubling effect. I know a lot of engineers use a pitch shifter plug–in set to detune by a few cents to do a similar thing, but the advantage of a pitch-correction plug–in is that it’s always adjusting the amount of pitch shift it applies, so the result has a much more random and lifelike quality to it. The slower the pitch-correction speed is set, the more subtle the result.

As Beren was using an iMac with no additional monitor screen, we also went over the benefits of using screen sets, which he was quick to appreciate. If these are created and saved in a Template song, they’ll always be available for future projects.

The plan was to leave at a sensible time to avoid the motorway traffic chaos on a Friday afternoon, which we spectacularly failed to do, but Beren did let me have the wood off-cuts from our endeavours to use in my stove at home, which was much appreciated!

Reader Reaction

Beren Matthews: “In a world of faceless Internet forum misinformation, Hugh and Paul’s wealth of real–world knowledge, plus their hands-on approach, was exactly what was needed. A priority for me was ensuring that the mixes for my band’s (Grip–Like Vice) new EP weren’t compromised by inaccurate monitoring.

“The improvements in monitor position, coupled with the tightening of the room response, mean I can be confident that what I’m hearing is significantly closer to the truth. Additionally, Paul’s extracurricular plug–in-related titbits provided some interesting ways of using the often–overlooked stock Logic processors. The Gate and Limiter have already proved scarily useful for slightly unorthodox tasks.

Baren Matthews enjoying his studio’s improved acoustics.Baren Matthews enjoying his studio’s improved acoustics.

“In short, Hugh and Paul’s knowledge and expertise is something that can’t be substituted by scouring the depths of cyberspace. Their help has been invaluable, and for me to be able to have confidence in my workspace is priceless.”

Published January 2015