Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems +3dB "LevelPerfect" Tweak Performance Improvement Poll

George thanks a lot for your great explaination and work.

Question: Are The movie presets Cinema/Discrete devoid of any clipping with +3dB? Even if a speaker is running as small and The LFE Channel is mixed in? No headroom needed there?

I have been using my center with eq1 all these years. I want to put it flat and listen to it and get used to it a little bit and go from there.

I have not measured it yet.

You know! If you sum two channels together as with the LFE channel the gain is +3db. What happens with +10db LFE? My guess is the 10db boost is thrown away.

You need a dolby digital test disc with the same frequency on both the LFE and main channels playing at the same time to check for clipping.

I made a test disc once to check LFE and bass management problems with the 568.2 on the old firmware that was configured wrong. Beta 2.5 fixed the problem. I could probably make a disc for you George! Actually I could just make a DD file and send it to you unless you have a DD encoder.

George! Have you tried creating an all digital speaker config that includes an LFE sub to see if all the channels are still -3db? I wonder if -3db is only for configs with no LFE or sub. Then another thought is what happens if your rears and center are set to small? Does Meridian throw away even more bits for headroom in the main channels?

Ron

George! Have you tried creating an all digital speaker config that includes an LFE sub to see if all the channels are still -3db? I wonder if -3db is only for configs with no LFE or sub. Then another thought is what happens if your rears and center are set to small? Does Meridian throw away even more bits for headroom in the main channels?

Ron [/quote]

No, I did better than that. I configured a 2 Channel system with 2 channel source (no LFE), No Mrc. And it still attenuated 3dB.

I also know that the system can clip even without the +3dB.

Even if LFE rerouting did cause a clip by having the same frequency on the LFE Channel (Full Scale) and a Front Channel (Full Scale), the frequency of that happening and the small harm it would cause compared to throwing out 3dB of resolution on all channels 100% of time is a no brainer to me. I'd just assume let it clip. Most often it would be LFE to TWO Large mains. So it would not be 3dB.

The only time I worry about clipping is if it's continuous. Occasional clipping is not a big deal (even Meridian says that in their DSP Speaker Manual).

Good CD's are even mixed sometimes with a little clipping. It's worth it to get the best dynamic range. Just like here CD mixers are willing to let things clip a little in order to retain as much fine detail on the bottom end as they can.

Yes but if no LFE it assumes LFE is summed with the main channels! Try two channel with an LFE configured to see if the -3db is eliminated. Just curious! Now that I think of it if only two channel what happens to the rears and center? I suppose the channels are all summed together in 48bit and adjusted to output the correct levels when converted to 24 bit.

Question: When LFE is routed to Large speakers, is it "summed" or is it "mixed".

The former makes no sense to me and the latter seems the only logical approach.


Also, with regard to the LFE level, in DD this channel is recorded 10dB lower than the main channels, so it requires a +10dB increase, just to get it back to reference level. Or am I mistaken in this?

Dan

LFE does not exist at all on a 2 Channel Source. So it has no reason to apply -3dB at all.

Yes it would be curious if have LFE sub vs not. But I can almost guarantee the 3dB will be there even if LFE sub exists. because if it's dumb enough to apply 3dB on 2 Channel Direct it will be dumb enough to keep the -3dB When LFE is never rerouted.

Small Rears can get routed to Large Center at the same time LFE gets routed to center. And Center can have +3dB (DSP Preset) and EQ on. And Bass Boosted and and and. And those could be all be full scale.

Yes the LFE is on a different Scale. That's why they created it, to go above 0dBFS. How you mix something on another scale that is not even in range makes no sense. The only proper way to do LFE gain is to have that amp for sub run at higher gain (in analog). When you start mixing the different scales together digitally I'm sure some compromises have to be made.

I just did a google search and found this. It's really quite complex.

http://www.audioholics.com/education/audio-formats-technology/0dbfs-blu-ray

Basically a full scale LFE channel cannot make a non LFE channel go above 0dbFS unless you have tons of head room. Some of that headroom (according to article above) is already built into the movie.

I think folks are worrying about rare conditions which is why I have not measured it. Just because in theory it could clip doesn't mean in practice it will.

Disregard my LFE comment with respect to the 10dB level... From Dolby's docs:

"The LFE channel carries additional bass information to supplement the bass
information in the main channels. The signal in the LFE channel is calibrated
during soundtrack production to be able to contribute 10 dB higher SPL than the
same bass signal from any one of the screen (front) channels. Even if all three
screen channels are active, enough bass could be delivered by the LFE channel
alone to bring the theatre`s subwoofer into acoustic balance with the screen
channels. This allows filmmakers to unburden the main channels by diverting the
strongest bass to the separate LFE channel, as needed. Under the most demanding
program conditions, where the bass is fully loading the left, center, and right
channels, the LFE channel could increase the bass intensity by up to 6 dB."


I've been missing the fact that, post-decode, the LFE Full-scale signal is louder than the main-channel Full-scale signals. My bad.

Dan

Summed is the same as mixed! If I take two channels and mix them in digital in a NLE on my PC I will have gain if both channels are playing the same frequency. What does happen with DD at least is there is some compression that takes place when the channels are combined into a two channels but the level does drop for added headroom. Actually when watching DD audio movies on SAT or Cable change the DD bit stream to 2 channel PCM in the SAT or cable receiver and the average volume will drop. This is why when watching TV sometime the commericials get loud. Two channel audio on commercials is played back much higher and the DD sound is reduced for headroom when mixing all the channels into two. At least today with HDTV it's all DD so it isn't a problem so much any more. Although I still hear it on the non HD channels on DirecTV from time to time. If you have a full 5.1 system there is no shift in SPL because each channel can play back at the level they are suppose to play back at. My LCD panel in my living room has a feature to keep SPL level even during commercials. Works great!