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Professional monitors in a box

In this week's tech review Professor Rumsey looks at the increasing demand for a decent set of headphones in the studio environment.

It’s increasingly likely that people making recordings do not have an acoustically treated control room with professional monitor loudspeakers. They have all the other gear, because it’s quite cheap these days, but good acoustics and decent loudspeakers are still quite hard to do. Couple that with the likelihood that the acoustic isolation of the average project or home studio is not that good, and you have a scenario that says “find a way of using headphones to do your mixing and not annoy the neighbours”. A good pair of headphones has an excellent frequency response, very low distortion, no crossovers to worry about, and effective acoustic isolation (at least from the inside out!). However it’s well known that stereo reproduction intended for loudspeakers doesn’t translate directly to headphones, requiring a certain amount of processing to simulate the correct binaural effect. Focusrite’s Ben Supper has been thinking hard about all this, for quite a few years, and the company’s recently launched VRM (Virtual Reference Monitoring) technology has incorporated a number of the things that he finds to be most important when trying to simulate loudspeaker monitoring over headphones. His recent lecture at the AES convention in London highlighted the importance of modeling specific aspects of the loudspeakers and the room in which they are located, so as to give a convincing impression. Among the key aims is to get the sound out of the head so that it appears to be coming from in front of the listener with a real room space around it. That way it ends up sounding more like loudspeaker listening. The first product in this line up, the VRM Box, is a small, high-quality USB audio interface whose software incorporates models of three different listening rooms and a number of alternative monitor loudspeakers. Among the factors taken into account when measuring and modeling loudspeakers is the off-axis response. As Supper points out in his AES paper on the topic, the critical distance (that beyond which the listener hears more reverberant than direct sound) is remarkably small in many real rooms, and can be less than a metre in a typical living room. The spectral balance of acoustical energy in this reverberant field is strongly affected by the off-axis response of the loudspeaker, so it’s important to get it reasonably accurate. However Supper also suggests that the law of the first wavefront (whereby we tend to suppress the effect of early reflections) helps to mitigate the effects of poor off-axis response. Focusrite therefore usually only measures the directional response in the horizontal plane. The loudspeaker responses were measured at fifteen degree intervals in an acoustically damped, but not anechoic room, 1.5 metres from the loudspeaker, using a windowing method to reject problematic reflections. In order to deal with the low frequency response, a near-field measurement was taken in front of the woofer. A crossover region between the near- and far-field simulations is arranged between 250 and 450 Hz. The first product has simulations of some popular large and small monitors (e.g. NS10, Auratone), as well as various hi-fi and budget types, in order that engineers can audition the effect of monitoring in a typical consumer environment as well as a studio. The results are said to be surprisingly convincing.