Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Cinema / Discrete / 10dB - definitive answers required!

Ok. Still doesn't explain why I'm losing 5dB of bass on multi-channel analogue vs. decoding the bitstream.

Indeed. Does this answer it?

From the link:

"SW analogue output from players
Okay, what level should the subwoofer output be? If it were just the LFE track, then you'd expect it, as discussed above, to be 10dB lower than the other channels to fit the 10dB higher maximum LFE output.

But if the player is performing bass management, then the subwoofer output also has to contain redirected bass; this extra signal could push the signal back above its nominal limit. To prevent overloading their output, or the receiver's input, players with bass management conventionally lower the SW output by a further 5dB. (This 5dB value is specified by Dolby, see references). Sometimes this 5dB drop switches in and out depending on whether bass management is being performed (ie if any speakers are set to SMALL).

The final SW output will typically be:

SW = LFE

or:

SW = Lower5dB(LFE + Lower10dB(Redirected bass)) = Lower5dB(LFE) + Lower15dB(Redirected bass)

So, in those two cases the SW output from the player will be respectively 10dB or 15dB lower than the other channels. A receiver should offer the ability to specifically boost the SW input on its multichannel analogue interface to compensate."

Ok. I can see that the LFE channel (!=sub) will be calibrated to hit 75dB at 10dB less input than the other channels. Any other bass (re-directed from the other channels) will not have the 10dB boost applied.

The next question is how this is handled in a Meridian system. Does the LFE channel always get a 10dB boost (unless Discrete is chosen) and the re-directed channels have no offset? Or is everything output to the sub raised by 10dB with the re-directed channels getting an additional 10dB reduction.

It's subtle, but it is the difference between Cinema adding 10dB of LFE and Discrete removing 10dB of LFE.

I don't think so, but it might give a pointer. I set all speakers in the Oppo bass management to "large". I need to re-measure what LFE I get with Oppo + Discrete (and re-check that it is -10 and not -15 or some other value that has fallen off the end of the meter).

You have to remember that the LFE setting on the processor is not referring to the physical subwoofer but rather the LFE source data stream.

So, my expectations of the bass management system would be:

CINEMA mode:
LFE: +0dB
Any channels mixed into LFE: -10dB

DISCRETE mode:
LFE: -10dB
Any channels mixed into LFE: -10dB

ie any channel mixed into the LFE stream always get -10dB because the physical subs will be playing 10dB louder than the main channel speakers and thus the offset is needed to keep the mixed bass at the correct volume.

Mark

This is exactly one of the reasons we'd prefer Meridian decode bitstreams in the processor for the HDMI stuff.

VK, how did you have the Oppo setup? With or without sub?

Be curious how your test would act if you had a sub. Why don't you have a sub yet anyway.

With sub. I'm pretty sure I disabled all bass management, but I'm going to check now.

I do have a sub (REL Strata III), but it's not working properly and I haven't got round to getting it fixed. Having said that, it's probably working well enough for this test.

Clarification from the Mothership would be helpful.

Ok. I suspect my Oppo issue is loser error on my part (it seems that the RS meter doesn't go below -10 on its dial!) and I bet that Oppo + Discrete will turn out to be -15dB.

In other words, the Oppo 980 is applying the -5dB adjustment on its analogue sub output even when the main five speakers are set to "Large". A bit annoying, but I'll be happy if that is the explanation.

Hopefully, many of us will be using HDMI soon. However, I suspect that the Oppo will also apply a -5dB offset to the LPCM sub channel.

This -5dB offset is going to be player dependent and is something for everyone to watch out for!!!

You must not miss it much then.

Can you boost the sub channel in the Oppo's channel trim settings? Does that fix it?

If I can find my 5.1 setup disc, I'll test this myself.

Yes and no. My HT basement room is so cluttered at the moment that I don't have the space to optimize sub placement. But I have been making great strides recently in terms of racking, re-wiring, etc. It was good for movies though as the bottom end response of the DSP33s isn't that great (though obviously impressive given the size of the box).

Better to fix it in my G68. Simple enough to add 5dB of gain to the LFE parameter.