Originally Posted by VarmintCong
ok, so setting small in the source introduces a crossover in the source?
When you set any particular speaker to "Small", the BM processor will apply a crossover function and route the bass below the crossover frequency to the subwoofer.
I set everything to large, and I think it helped a little, but still doesn't sound any better than optical. I will try more discs though, see if I can notice a difference. Optical still has more bass, I think the bass is still a little low even with 10 dB differential in the source.
If you are also doing BM in the source device, then you will need a LFE/sub boost of more than 10 dB - probably on the order of 13-15dB.
This is not immediately obvious (clearly), but there are a LOT of good reasons not to do Bass Management in the source device. Here's 1:
The LFE signal from the decoded 5.1/7.1 audio will always be encoded 10 dB lower than the other signals. This is designed to provide more headroom without overdriving the subwoofer's input.
HOWEVER, when you apply BM and mix in redirected bass from the other channels, they must be reduced by 10 dB to match the LFE level. Make sense? (Some source devices still get this wrong.)
OK, so now we have combined LFE and BM bass at -10 dB. Trouble is, if you have heavy bass in the mains AND and peaking LFE signal, the combination of the two can overdrive the sub/LFE signal. Thus, the combined signal must be lowered by another 3 dB to maintain headroom.
If you use BM for all of the signals (mains, surrounds, center), it gets even worse. In this case, the combined sub/LFE signal may be as low as -15dB or even -18dB (depends on the processor).
Now, to top it off, you have a receiver that doesn't do Bass Management on the analog inputs, but also won't allow you to trim the levels individually by input source. Given that you absolutely know that the sub/LFE needs a variable additional boost somewhere between 10 and 20 dB, this is a terrible limitation. The easiest work-around is to simply lower the main/center/surround levels in the source device's settings, but this degrades the mains signals.
In truth, you are unlikely to find this information in the manual(s). To be honest, the implementation of bass management in source devices is often incorrect, rarely documented, and terribly inconsistent from company to company and product to product.
Keep in mind, though, that the real problem is with the RECEIVER, not the source device. The receiver isn't allowing you to to BM in the receiver - where it SHOULD be done, so that you can maintain all of the analog signals at maximum level without clipping.
Under any circumstances, since you can't depend on consistency in analog multi-channel levels using source-based BM, the only thing you can really do is to:
1) Use a calibration disc (DVE, Avia, etc) and SPL meter to set and match the levels at the receiver using a different source device.
2) Use a calibration disc and SPL meter to set and match the levels for the multi-channel source device. This time, only adjust the levels at the source device.
It's a hack work-around, but it's the only thing you can do given the system's limitations.
FWIW, there is a very long but informative thread over in the HD DVD hardware section. The HD-XA2 had a severe firmware bug in the original LFE/BM implementation; it got worked out in a later revision, but was still off by a dB or two in the surrounds. Several of us here got VERY involved in figuring out exactly what was happening with the XA2, and there is a TON of good information in that thread.