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‘Lin-Ear’ monitoring

Focusrite's virtual reference monitoring: how does it work?

Monitoring and room correction increasingly go hand in hand, with a growing number of solutions on the market that combine delivery of audio with some kind of digital analysis of the target space and automatic calibration. So far, however, all of these solutions have presupposed monitor installation. The software is intrinsically linked to speaker cabinets. UK manufacturer Focusrite has now proposed an alternative relationship between monitoring and software, for situations when monitors themselves are neither available nor practical: Virtual Reference Monitoring (VRM) is a proprietary loudspeaker and room simulator designed for headphone listening. With no need for correction per se, the software performs a very different kind of modelling. The system has a menu of presets, representing 10 different pairs of industry standard nearfield and main monitors in an acoustically treated control room. It also simulates two alternative rooms: a large living room and a smaller bedroom. For these the menu provides a further range of speakers, from quality hi-fi to computer, low-quality stereo and television speakers. In all cases there’s a choice of listening positions, too, both for accurate stereo imaging and to imagine how the mix is compromised by typical room behaviour. The direct sound is reproduced binaurally by standard headphones, while the DSP gets to work on the simulations. These have been generated by linear convolutions of impulse responses measured from the actual monitors they represent, as Focusrite’s Ben Supper explains. “What we’re simulating is the frequency and phase response of each loudspeaker,” he begins, “and then the directivity. For these we took a series of accurate polar plots at 15° intervals, and in fact these are the biggest distinguishing factors of each monitor. The way they sound is generally to do with the radiation pattern. Most of the energy you hear in a room is reverberant, so it’s essential to get that right.” From around 20 brands Focusrite has selected 15 in the final suite of simulations, according to both practical and marketing criteria. The TV and desktop multimedia speakers, which are “awful in different ways”, according to Supper, do still have a similar sound profile – not least in delivering almost nothing below 250Hz. And yes, NS10s are included, as are the classic Auratone 5Cs and BBC LS3/5As. The room modelling is convolution based on a rectangular space containing simple virtual objects, using early reflection models obtained by bouncing signal off perpendicular surfaces. “We judged the angle, time and material path taken by the signal,” Supper continues, “with some air absorption taken into account. But it’s a trade off between two algorithms: extremely accurate early reflections; and more general, psycho-acoustic later reflections. You need both to get convincing room and distance cues.” You can test VRM out for yourself with your own headphones, online, at Giles Orford, Marketing Director at Focusrite Audio Engineering, sums it all up. “For those without an unlimited budget, with young children or aurally sensitive neighbours,” he says, “VRM places an alternative but equally perfect auditioning environment within reach of the masses.”