Magic at Mechanics

Prof. Johnson and the Ledins Record Rachmaninov

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Magic at Mechanics

At 7 p.m. on Labor Day, I was sitting at a table in the empty lobby of the Hilton Garden Inn in Worcester, Massachusetts, waiting to speak with Reference Recordings engineer Keith O. Johnson. Across from me was RR’s public relations director, Janice Mancuso. She’d promised to produce “Professor” Johnson at six-thirty, but after 27 years at her job, Mancuso knew better. The Reference team had access at Mechanics Hall a few blocks away until seven and was using every last second on this, their first day of recording an all-Rachmaninov program with the Hermitage Piano Trio. A few minutes after the hour, Mancuso’s phone chimed. She turned the screen in my direction to show me a two-word message from Reference’s Vice President of Operations JoAnn Nunes: “Herding cats.”

Moments later, the doors to the hotel lobby slid open and in walked the felines in question, including Johnson, Nunes, digital engineer Sean Royce Martin, and producers Victor and Marina Ledin. (Executive and Managing Director Marcia Martin was back in San Francisco minding the store.) Keith Johnson is now close to 80, but if he was the least bit worn out from ten hours of set-up and recording, it wasn’t obvious; in fact, he seemed energized. Johnson has worked in Mechanics Hall previously—the Renaissance Revival-style building, constructed in the 1850s and restored in 1977, is a favorite recording site for labels big and small. Asked to describe the sound of Mechanics Hall, Johnson characteristically begins his answer with a subjective impression that progressively becomes more specific and quantitative. “It has a glow, an aura, a solidity that can have a lot of power. You can clearly tell the walls are heavy. It has a ‘tail,’ and a tail is a very, very important part of the concert experience. Say, on piano, you play a note loud. The string vibrates to the limit and vibrates a little faster—so the note has a slightly higher pitch than it would have if it were played softly. The fundamental and harmonics drive the hall hard and this little tail happens, which is probably two or three times longer than the main hall reverb. As the note decays, you have two slightly different frequencies going. It creates what’s called a “sublime harmony” effect—it was described originally, I think, for music boxes. It’s a little undulation of sound that kind of floats. Pianos are particularly good at it; some woodwinds and other instruments that are overblown do the same thing. It’s part of what Mechanics Hall does very well.”

The following morning I headed over to the hall to observe the second of three days of recording. The large room was devoid of any seating on the main floor—the space can be used for weddings and exhibitions as well as concerts, and the chairs are removable. Onstage, a variety of microphones, mostly vintage Sennheisers rebuilt by Keith Johnson, are mounted on stands. (The exception is a pair of Coles 4038 dynamic ribbon mics, positioned in front of the piano.) “I have a direct-to-two-channel setup, which is how we’ve done most of our recordings. It kind of resembles a Decca tree, except that the center is a stereo microphone, not a mono. I will very likely have two sets of outriggers instead of one. Almost always, there will be a set of hall microphones that will tie it together. And these days, I use head-related transfer function EQ.” Johnson continues: “I’m recording for three different formats. Surround is certainly one of them. Two-channel for loudspeakers and two-channel for headphones—they are not the same thing.  I feel very strongly that the industry has to adapt because I can do my best work knowing ‘OK, this one’s for playback in a living room setting’—and I can do things that, for headphones, would be very bad, bass in one ear, for instance. Binaural headphones, on the other hand, can create a very immersive experience.”

Prof. Johnson had with him a diagram of his microphone setup, and I thought I might be getting some kind of a scoop when he said it would be fine to take a photo of it with my phone [see photo]. But, downstairs in the hall during a break, I realized that this was less of a coup than it might have seemed. The final disposition of the dozen or so microphones on stage was only a vague approximation of what was on the piece of paper. The hall mikes had migrated to the stage and the main arrays were wildly asymmetric in their right/left positioning, the result of extensive experimentation the day before. Clearly there’s a lot of empiricism to Prof. Johnson’s methodology—but no guesswork. Here’s KOJ’s explanation regarding his choice of just one set of microphones noted on the diagram: “Aux OM is a moderately bright semi-directional pair for glow or air that can be reproduced when string sounds bounce from an overhead proscenium. Their left and right signals were reversed to help compensate for a ‘ping-pong effect’ from the rove accents.” Many decisions of this kind informed the seemingly chaotic deployment of musicians and microphones on the Mechanics Hall stage.


A bundle of cables from Johnson’s hand-built microphone preamps wends its way approximately 200 feet to the control room several floors above the stage where the musicians are warming up. There, Johnson sits near the front, a few feet from a video monitor that gives a view of the stage. (In a row behind Johnson are Sean Martin, the Ledins, and JoAnn Nunes—the first managing four Pacific Microsonics Model Two A-to-D converters running at 174.4 kHz/24-bit with HDCD encoding, the other three with open Rachmaninov scores.) On a couple of small tables sit the home-brew mixers that have helped Johnson achieve acclaim in the recording world. The main two-channel console is a small, unprepossessing box with a few dials across the front. “I think I built that thing 30 or 40 years ago. It has almost nothing in it—just a bunch of variable resistors with controls, switches, and one little amplifier. That’s all it’s got.” That box sits atop a surround sound configuration and there’s also an “accent console” for inputs that are going to be used sparingly. A pair of moderately sized stand-mounted loudspeakers, again designed and built by Johnson, has replaced the hefty B&Ws that are usually used at Mechanics.

One is struck that nowhere on Johnson’s grouping of equipment is any sort of display or screen. “No meters, no lights, no waveforms—just a few controls that are dedicated to massaging or moving the picture,” he told me. Over the years, it’s been suggested that Keith Johnson has been secretive about his engineering techniques, but I don’t believe that this is his intent. Of course, plenty of audio engineers (and, for that matter, high-end designers and manufacturers) have a “secret sauce” that they treat as proprietary and guard jealously. But as thoroughly grounded in electrical engineering as Keith Johnson is, there is a significant in-the-moment creative aspect to the way he gets his consistently excellent results. Johnson adjusts the mix on the fly, as the music unfolds, a technique he calls “dynamic mixing.” The Professor will be a tough act to follow because I doubt he’ll be leaving precise recipes behind.