Tech Focus: Remote Audio Monitoring, Part 1 — Automated Calibration Becomes the Norm
By: Dan Daley, Audio Editor, Sports Video Group
The latest must-have in audio monitoring is computerized automatic speaker calibration: the use of automated equalization, timing delay, level control, and other parameters to more precisely control the acoustical characteristics of small monitoring spaces.
That capability has certainly helped Genelec keep what is widely regarded as a market-leading position in outside-broadcast production trucks for its self-powered speakers. Integrated into the company’s SE (Small Environment) speaker line and using a factory-calibrated acoustic-measurement microphone, Genelec’s Auto-Cal feature aligns levels and compensates for distance differences and provides two parametric DSP notch filters, with room-response controls built into the loudspeaker hardware. The SE7261A subwoofer uses four parametric DSP notch filters and bass roll-off controls and can adjust correct crossover phase for the subwoofer on the network.
The newest member of this club is Blue Sky, which told SVG last year that it would be developing its own automatic-speaker system. Prototype systems are expected to be field-tested this month, with production models ready for the fall. What Blue Sky calls Speaker-Room Optimization (SRO) includes an equalization section built into its SAT 6B and SUB 12D speaker systems, including a 31-band graphic and eight bands of parametric EQ/filters. A room-measurement subsystem is built into the speaker system’s subwoofer. Precise measurements taken using a calibrated microphone are sent through Blue Sky’s equalization software, running on a Windows PC. Corrective equalization curves can be automatically generated or manually adjusted. When SRO is used in conjunction with Blue Sky’s new Audio Management Controller (AMC), multiple curves can be saved and recalled.
Chris Fichera, VP of audio, Group One Ltd., which distributes Blue Sky, stresses that the system works across the entire audible frequency range. “SRO can measure and correct for room anomalies across the full spectrum, not just the low end,” he says, underscoring how auto calibration is becoming a new point of comparison in the highly competitive audio-monitoring market.
But it’s also part of a mission that manufacturers see themselves pursuing: to make monitoring in the cramped quarters of a remote-production truck more accurate and less challenging. Size has always been an issue, and loudspeakers are at the distant end of what has become a virtually all-digital audio-signal chain, where digital audio has to transform back into analog and become vulnerable to the harsh acoustical reality of confined spaces. A typical audio-mix compartment in a truck might be 6-8 ft. deep; a 50-Hz sound wave requires just over 22 ft. to fully cycle. That’s propelling the uptake of subwoofers in even the smallest trucks.
JBL’s Room Mode Correction (RMC) system, available for all the company’s LSR series speakers, compensates specifically for low-frequency irregularities with a system that measures the room’s frequency response and applies corrective filters.
Peter Chaikin, senior manager of recording and broadcast marketing, JBL Professional, points out that, while automated tuning of monitoring systems is becoming more important, just as critical is how monitor speakers interact acoustically with the vehicular mixing environment. “Above 300-400 Hz, DSP has nothing to do with it,” he explains. “At the low end, the room is in control; above 300 Hz or so, it’s about acoustical directivity, making sure that the speaker’s response is consistent all the way up the spectrum. The key is a mathematically correct waveguide. You can’t do that with EQ.”
But managing that low end has become critical. “Without a subwoofer, you’re going to be missing a lot of noise, such as wind, that viewers at home with subwoofers will be able to hear,” says Fichera, noting that many small- and mid-market trucks lack subwoofers in their monitoring systems. Precisely for that market, Blue Sky expects to soon introduce an even smaller, 2.1 monitoring system, which will be based on its Media Desk system used in postproduction and will also incorporate the SRO calibration feature.
Placing the DSP for automatic speaker calibration in the subwoofer has become a widely used strategy to minimize the space that more-complex systems take up. That sub-as-processor is also becoming an interface for what manufacturers expect might be audio arrays bigger than 5.1 someday. For instance, Will Eggleston, director of marketing, Genelec, points to the eight AES I/O ports on the SE system’s subwoofer. He doesn’t expect 7.1 to hit television very soon, but the interface is becoming more widely available if it were to; Blue Sky’s subwoofer also offers eight I/O.
For now, though, automatic speaker calibration remains the latest gee-whiz on the audio side of the truck. It definitely adds to the cost of monitoring systems — Eggleston estimates that it boosts the price of Genelec’s SE systems about 30% — but manufacturers say they are not getting any pushback from truck builders and their customers. “It’s a feature the market wants,” he says. “No one is saying leave it off.”