Originally Posted by BGLeduc
I would note that in my room ARC computes a Subwoofer LPF of 200 rather than the 120 that Dr. Rich said is typical. It appear that ARC selects that value based on the measured in room response of the sub. There should be no content up that high, as the .1 channel is limited to 120 regardless of the LPF, right?
True, there should
be no content up that high, but I have found cases with LFE content >700 Hz. It was an obvious error -- forgot to apply the LPF to the LFE content.
Just as THX tells us to totally bypass any LPF inside a powered subwoofer (when possible), the 200 Hz setting gets the ARC LPF out of the way so that the 120 Hz bandwidth of the LFE channel can pass with minimal alteration.
I am still curious if the LPF that is in the BM menu remains in play when you load an ARC profile. While the crossovers shown in the BM menu reflect that settings from ARC, the LPF does not. Is it in series with the ARC computed LPF or is it only used when an ARC profile is not used?
In my AVM60, the LPF for LFE in the speaker setup menu shows the same 120 Hz value as in the ARC program. Might just be a coinkydinky. In any case, I believe these filters are in series, and are both used all the time unless you manually set the AVM60’s filter to Bypass. More on that below.
Originally Posted by dkuster
But if the subwoofer cutoff in the targets menu only applies to the LFE, then what is the purpose of the "subwoofer LPF for LFE" entry in the bass management setup menu?
I did not say the Sub cutoff only applies to LFE. It is only touching LFE if the filter is set >100 Hz and the speaker crossovers are <80 Hz. Based on the presented curve after calculation, it clearly applies to the redirected bass if one pulls it down low enough, like 50 Hz. There is some question as to whether this filter applies to LFE at all. I suspect it does, but have not done that test.
In most DSP chips, there is a LPF for the LFE channel, which is separate from any EQ filters applied. That makes sense, as the filter in the ARC program is not labeled as an LFE filter – it is a subwoofer EQ filter.
And in the AVM60 we also have the option for Bypass of this LFE filter. That is further indication that this is a separate filter from the one ARC uploads, as bypassing it does not kill the subwoofer EQ.
They do not appear to be the same thing, because I can set "subwoofer LPF for LFE" to 120 Hz, do an ARC run and have subwoofer cutoff be autodetected as 80 Hz, and when I upload the configuration to my AVM60 "subwoofer LPF for LFE" is still its original value (120 Hz).
Yes. These are different functions, so can have different settings.
My totally baseless theory is that the only processing applied to the LFE channel is simple low-pass filtering at the "subwoofer LPF for LFE" frequency. No ARC room correction is done on LFE content.
I don't know much about ARC, but I am quite certain that ARC is applied to the LFE audio.