Originally Posted by Bob Pariseau
A correction here. The LFE/Subwoofer multi-channel analog output of the Oppo Blu-ray players is -15dB down compared to the other channels, not -10dB.
Of that -15dB, -10dB comes from the way LFE is recorded -- allowing headroom for *LOUD* bass. The other -5dB is applied by the player to allow headroom for bass steered in from other speaker channels.
In the Oppo implementation, the -15dB holds true WHETHER OR NOT you have bass steering happening on the multi-channel analog outputs. I.e., whether or not all speakers are set to Large or some of them are set to Small.
Most AVRs will automatically apply +10dB boost on their multi-channel analog LFE/Sub input. That leaves +5dB to go. Some AVRs allow you to adjust the boost with typical choices being 0dB, +5dB, +10dB, and +15dB. +10dB would be the default for such AVRs and, +15dB is the choice to use with the Oppos.
If you can't get the correct boost in the AVR, and if the AVR is of the common type that applies volume trims only to digital audio (and NOT to the multi-channel analog audio), then a practical approach for dealing with this is to set the Sub output trim in the Oppo to 0dB, and then adjust the volume knob on the subwoofer itself using an audio calibration disc like the AIX Audio Calibration Blu-ray. That would mean you would be RAISING the volume on the sub by +5dB or +15dB depending on wether your AVR provided the standard +10dB boost on that path.
That's fine for analog but screws up the sub for your digital audio sources, so now you use the volume trim in the AVR to REDUCE the sub output from your digital audio sources to compensate for the raising of the volume knob on the sub. And that leaves everything properly balanced.
You don't want to raise the sub volume trim in the Oppo because that undoes the headroom that's been designed in. I.e., loud LFE passages mixed with loud steered bass contributions from the other speaker channels may cause the input to clip in your AVR (or sub if directly connected to the sub).
However if you are NOT doing bass steering in the Oppo -- that is if you have ALL speakers in the Oppo set to Large -- then the extra -5dB attenuation applied by the player is not needed. In which case you can safely use a +5dB subwoofer volume trim in the Oppo to undo that. And that, combined with the standard +10dB boost typically applied by AVRs, will get you where you need to be.
All of the above applies ONLY to the multi-channel analog outputs of the Oppo. This stuff is handled automatically for digital audio.