Audio Calibration

Anthem Room Correction (ARC) System - Part 1


Room Gain

Room Gain is an option on the advanced control option in the control panel shown at the beginning of this review.

The room dominates the response of the speaker in the absence of electrical room equalization (a topic discussed in my article titled Subwoofers: A Brief Look at the Effectiveness of Using a Subwoofer in a Music System). The room gain is an increase in the average response below 200Hz relative to the mid-band response (average 300Hz -2kHz). A room has no genuine gain; a better term is preservation of pressure (term developed by Tom Nousaine as explained in my article noted above).

As you see from the measured data above, when the low end frequency response variations are reduced, the amount of bass energy in the room goes down. Some people would like some of that energy restored, finding the corrected room lacks bass post correction. The ARC Room Gain panel adjustment is designed to restore the bass energy some people believe is missing.

Some room EQs attempt to simulate the room gain by supplying a shelf to the equalization curve around 200Hz with an increase of ~2dB below 200Hz. The Anthem is much more sophisticated in that it can vary the frequency at which the shelf begins, vary the limit of the response increase below the shelf, and vary the frequency of the roll-off of the woofer. The figure below shows what happens when ARC Room Gain is applied.

In this example the "Auto Detect" function was used. With Auto Detect, ARC calculates the value of ARC Room Gain parameter to most closely match the room's pre-correction characteristics while still maintain a smooth bass contour. Note that the Response Cutoff control option was moved from flat to 70Hz. ARC also uses this option to shape the overall bass response to match the pre-correct response. Response cutoff applies a 2nd order Butterworth filter at the frequency entered. Response Cutoff has a different function when a subwoofer is deployed as we will see in Part II of this review.

Subjectively, I am not a fan of room gain. If the goal is to reproduce what was heard at a live event, why would I want to add a bass boost that is a property of the small room I am listening in? One could call this the "we are at the event" perspective. The alternative perspective is the "performers are here in the listening room". Perhaps this is plausible for a very small group but even a chamber orchestra has no chance of fitting into even a very large living room. The takeaway is you do not have to agree with me. ARC allows you to pick both options, and you can adjust it for something down the middle just by changing the panel settings.

Notes on High Resolution Signal Processing:

The Anthem D2 and AVM Pre/Pro products that have ARC will process an incoming signal at its native rate up to 96k samples/second. Robert Kozel verified this by using a 30kHz test signal sampled at 96k samples/sec on an Anthem D2. He did the same test with the new Marantz AV8801 Pre/Pro that has Audyssey MultEQ XT32 room correction. The AV8801 did not pass the 30kHz signal because it down-sampled the high resolution test tone to the standard resolution of 48k samples/sec. The Marantz AV8801 is $3,600 before the costs of having the unit upgraded by a Marantz certified Pro Installer using the Audyssey PC based tools and calibrated microphone. Sampling at 96k sample/sec requires twice the DSP resources for the real time filters used for room correction.

Here are graphs (all graphs shown below were produced by Robert Kozel) to illustrate that the Marantz Audyssey processing does not pass 30 kHz, which it otherwise would if digital down-sampling to 48 kHz were not occurring. The signals were 24/96, which is the maximum sampling rate that the Audyssey will accept.

First, an 18 kHz and 30 kHz set of test tones with Audyssey turned off. Note that both test tones are seen in the output.

Anthem Room Correction Article


Now, a graph with the same set of test tones, but with Audyssey turned on. Note that the 30 kHz signal is no longer there. That is because the signal has been downsampled to 48 kHz, and the maximum analog frequency that can be passed through to the output is 1/2 of that, which is 24 kHz.

Anthem Room Correction Article


Further, here is the frequency response of the processor with Audyssey turned off. Note that it is reasonably flat out to 45 kHz.

Anthem Room Correction Article


With Audyssey processing turned on, the frequency response drops off beginning at about 23 kHz, and is there is no signal beyond about 26 kHz.

Anthem Room Correction Article


The Marantz AV8801 has three 4th generation Analog Devices ADSP21487 DSPs which provides as much digital signal processing capability as found in any Pre/Pro using Audyssey MultEQ XT or XT32 room correction that I know of. I expect many and perhaps all Audyssey MultEQ XT or XT32 enabled products, including those at higher price points, will also down-sample high-resolution material to 48k samples/sec when the room correction is enabled. The Sherwood R-972 with Trinnov also down-sampled high resolution material to 48k samples/sec.

Anthem’s lower cost MRX AVRs do down-sample to 48k Samples/Sec.