Using the Auto Set-up and EQ Features in an SSP or Receiver

[Sonnie]

Introduction

Many surround sound receivers and processors these days offer an "Auto" set-up routine that attempts to configure the basic set-up for the consumer, including whether a speaker should be high-passed or not, which frequency to high-pass it at if applicable, the distance/delay setting for each speaker, and of course the calibrated level (loudness) for each one.

The process often includes EQ for some or all of the channels, usually with the tag that doing so "corrects the room". Seem like a good idea? Yes, a great idea, but when it comes to the practical application in a real room, the results can leave much to be desired.

In such systems, the manufacturer supplies a microphone with known anomalies that can be accounted for in the calibration software. You plug in the microphone, place it at a listening position, the system cycles test signals from different speakers, comparing what the microphone picks up to what it sent to the respective speakers, in terms of time arrivals, frequency response, phase response, polarity, etc., and then applies 'correction' in the form of compensatory delays, level-matching, polarity swaps (if necessary), and frequency response equalization as best it can to make up the difference.

So what's the problem? In terms of setting delay and matching channel levels, if the software/microphone combination works correctly, nothing. It should still be verified with manual calibration (because sometimes these systems produce inaccurate adjustments, or you might want to fine tune it after the fact), but in handling the basics, there's no reason why this portion of the auto set'up can't work just fine. The problems really arise in "Auto EQ."

"Auto EQ" (a.k.a. "Room Correction"), in many cases, ranges from a marginally helpful 'band-aid' to useless or severely detrimental alteration.

All rooms start as inherently flawed in terms of acoustic transparency. If they've got walls, floors, and ceilings, and most do, they have surfaces that offer reflections in additional to the direct sound that, assuming a reasonably good loudspeaker, we want to hear primarily, if not almost exclusively. Getting a room that controls these reflections through deliberate absorption and diffusion (dispersed reflection) treatments (use of wall and ceiling panels, i.e., Room Treatment) is a mixture of science and art. Note that, for the sake of discussion, we differentiate here between "Room Treatment", which we define as the use of physical objects in the room (absorption and diffusion panels), and "Room Correction", which we define as the DSP applied in SSPs and receivers to change the sound that you eventually hear. We have a previous article on the types of materials used in room treatments.

There are many consumers who have actually spent time and effort addressing acoustic issues by using room treatments in a sound system who will testify that it's a far more fruitful upgrade than the time and money spent swapping out cables, components, or even loudspeakers. Of course, actually doing this, compared to playing audiophile nervosa, is a real effort, an effort most consumers, and even hobbyists, will not tolerate, and are eager to rationalize into the lowest possible priority. In extreme cases, some would rather debate about refining their sound with digital audio cables than talk about slapping up some rigid fiberglass panels on reflective surfaces.

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