Originally Posted by Mark Seaton
One other often overlooked limitation/quirk of ARC I only became aware of after Roger Dressler & I were tinkering with Kris Deering's system is that once you run/engage ARC, the subwoofer low pass is fixed for all channels. In other words, regardless of if you set the crossover for your mains at 40 Hz and your surrounds at 100 Hz, if you left the LFE/sub channel correction and low pass at 120Hz in the software, the low bass info from every channel will get routed through a 120Hz low pass. This can create a lot of overlap with the speakers and muddied sound if you don't know how it is behaving.
If you turn off ARC, bass management behaves as we would expect, where the low pass from each channel is routed through a low pass corresponding to the crossover setting.
The result is that you mostly need to choose a global subwoofer low pass for all bass content in the system. With this understood the results can sound very good. Hopefully Anthem will decide to make the software fix to this bizarre, unexpected, and undocumented behavior, but be sure to understand this before trying to make a comparison to Audyssey.
Bass management is a function of the DSP, not of ARC aside from its selection of the xover frequencies, and the "bizarre and unexpected" configuration, where all channels not set to full range are summed with LFE before being run through LPF, is indeed documented, though in the confidential Dolby Consumer Decoder Licensee Information Manual. The Freescale DSPs, formerly known as Motorola, work like this. The Anthem AVM/D models use them. As of AVM 20 v2.1, an additional control is provided such that LFE can bypass the crossover if the user chooses to do so, which means only the redirected bass is routed through LPF. For the models that use ARC (AVM 40/ARC and later, and all Statement models), the LFE bypass is in effect when ARC is on, regardless of the LFE Xover Bypass menu setting. (Behind the scenes in either case, there's compensation to prevent the wild frequency response that would result if summing a signal with its filtered, i.e. phase-delayed, counterpart should the main channels and LFE channel contain the same info.) It's possible that while you were toggling ARC on/off, you were also toggling the LFE crossover control.
MRX x00 (Gen 1) models use a completely different DSP, and this one sends bass to the subwoofer according to the xover frequencies set in the other channels, in other words according to your expectation which also means that the comments about the bass management are irrelevant to all MRX, a model of which was the subject of kbarnes701's comments.
MRX x10 (Gen 2) models use yet another completely different DSP, which in this regard works like that of MRX Gen 1 except that there is an additional control for dialing in LFE xover frequency, and not to be confused with sub channel xover frequencies. Like the bypass control in AVM/D, its purpose is to prevent LFE from being rolled off prematurely as would be the case if xover frequency was determined by a combined sub+LFE control set to, for example, 40 Hz.
Note that sub correction range, also called cutoff range, shown in the targets window of ARC software, both versions, is not the sub xover frequency. It's in essence the range that's worth eq'ing. ARC avoids wasting resources in trying to make speakers play something they can't play, for example, if the sub has little in-room response above 80 Hz, ARC may set the LFE xover in the MRX Gen 2 menu to 120 Hz, more or less a bypass, while the eq cutoff is set to 80 Hz in the ARC software and rolled off accordingly. These two parameters work in concert such that two 80 Hz xovers wouldn't cascade one another.
Some of this is of course is not immediately apparent, even counter-intuitive, although using ARC-2 software, which applies to MRX Gen 2 and has more visuals than ARC-1 software while changing targets, makes it easier to understand.
For any additional questions or concerns, please contact Anthem directly as I am not a regular follower of forum discussions. This one came to my attention from a reader of the MRX 710/510/310 thread on AVForums (UK) after Mark Seaton's comments were copied there.