Of course, the frequency and phase response of the hardware interface (its preamps and converters), is included within the acoustic measurement loop, so the more neutral and accurate the interfaces sound quality, the better.Every room suffers from low-frequency (LF) modes, the low-frequency peaks and dips that are caused by sound waves bouncing around inside the room producing interference patterns.
Traditionally, since the LF room modes are caused by physical reflections, a physical solution is normally employed specifically, bass trapping and broadband absorbers. These soak up the sound waves energy as it approaches the walls, so there is nothing to reflect, and thus nothing to cause interference peaks and dips in the room. Consequently, quicker, easier, electronic fixes for room modes have been sought for as long as the problem has been recognised. The earliest version was simple equalisation measuring the rooms response at the listening position and applying an inverse response to the monitor speakers amplifier chain using an equaliser. For a start, the rooms response varies enormously throughout its area, because different reflected frequencies interact with each other in different places. So moving the measuring microphone a small distance one way or the other typically produces very different corrective response plots. The perfect equalisation for the measured position may well end up making the situation far worse at other positions in the room. Another problem is that response irregularities caused by cancellation nulls (where reflected sounds arrive in opposite polarities and cancel each other out) can produce very deep response notches often 30dB or more. Equalisation cant easily address this, partly because the amplifiers and speakers are unlikely to be able to generate sufficient energy to fill those dips, but also because if a dip is caused by reflected waves cancelling each other out, more energy wont resolve the problem, as the cancellations will still occur. More significantly, room modes arent just about frequency response. Were dealing with resonances here, which means stored energy and time-domain responses, often referred to as modal ringing, which normal equalisation cant address. For all these reasons, simple monitor EQ is rarely effective for correcting a rooms inherent acoustic issues, but it can be useful in fine-tuning a room which has already been properly treated to resolve the major room mode and reflection issues. The more sophisticated the approach, the better the results are likely to be. Digital equalisation can provide incredibly narrow response peaks and notches, along with precise phase correction and, to some extent, simple echo-cancellation, so the ideas of electronic room-correction are becoming popular again (many monitor systems now include some kind of digital room-mode correction facility). Overview IK Multimedias ARC advanced room correction system works as a software plug-in for DAW-based studio environments. The room is measured using the supplied mic and analysis software, which calculates the necessary corrective equalisation. The DAW plug-in (which comes in VST, RTAS and AU formats) uses the calculated response to correct the output from the monitoring system. The system is called the Audyssey MultEQ, and in these hi-fi applications is able to correct surround sound installations as well as stereo setups, so presumably a surround sound version of ARC may become available in the future. It is claimed that the MultEQ system analyses patterns in the frequency- and time-domain responses, measured at multiple points around the listening area, and then generates correction responses for each channel, so as to optimise overall accuracy across as wide an area as possible. Pattern-recognition and fuzzy logic algorithms are involved Audyssey dont give much away in their explanations, but they do explain that the MultEQ process uses time-domain based FIR (Finite Impulse Response) filters, with the emphasis on resolving low-frequency irregularities. Ik Multimedia Arc System Manual And AARC Package The software application comes on a CD-ROM, and theres also a manual and a tough plastic case containing a small-diaphragm electret measuring microphone (with foam windshield and stand adaptor) which requires phantom power. ![]()
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