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

Joel,

So your tests confirm what the manual says - DISCRETE gives a -10dB cut and CINEMA does nothing to the incoming signal? And thus the 10dB boost is in the LFE mix?

As for 4), looks like a bug in the Oppo?

Mark

Actually, Tommy's (superb) link nails it:

"So at all points in a system - analogue interconnects, PCM signals, encoded Dolby Digital - the LFE channel is "10dB too low". A 75dB SPL signal on the LFE channel will be 3 times, or 10dB, smaller than a 75dB SPL signal on the other channels. It will only sound correct when fed to an amplifier that amplifies LFE by 10dB more than it amplifies the other channels."

I knew this, but had forgotten it; hence my confusion above... honest

The LFE channel is calibrated to playback 10dB louder. The actual mix doesn't have the boost. So when played back on a properly calibrated LFE channel the 10dB is added. In a system without an LFE the processor I guess will have to add 10dB to the signal when it mixes it into the LARGE speakers...

Mark

More from that link:

LFE digital output from players
When outputting a Dolby Digital or DTS bitstream from a player, the LFE channel remains encoded in the bitstream, untouched by the player. The receiver's decoder has the responsibility to boost the LFE by 10dB, and almost invariably they will get this right. DD and DTS remain the most foolproof way of transmitting LFE.

When outputting a PCM multichannel bitstream over Denon Link, i.Link, HDMI or similar, the LFE channel will be transmitted "as-is", and will need boosting by 10dB in the receiver. The receiver should do this automatically. If it fails to do this before performing bass management, then you will be unable to calibrate the system correctly - boosting the subwoofer to compensate will have the side effect of over-emphasising bass from other channels.

My tests confirm a real 10dB difference in the LFE level between the Discrete and Cinema presets.

How can it be? The LFE level from the Oppo doesn't change when applying different G68 presets. The LFE levels measured from the Oppo + Discrete and from the G68's decoder + Discrete are identical. My conclusion is that the Cinema preset is applying +10dB to LFE when decoding internally and only +5dB to m/channel analogue inputs.

So Cinema must be *adding* 10dB and Discrete does not.

In your case, yes, because you are folding the LFE into your main speakers. But in a system with an LFE, the subs will be calibrated to be 10dB louder than the main speakers and thus the sub itself is doing the boosting...

Mark

It shouldn't make a difference whether or not I have a sub. Meridian has stated that it will not allow us to lose bass. I detect a 10dB difference between Discrete and Cinema when I decode in the G68, but only a 5dB difference when I use the analogue input. This suggests that some of my bass is being lost in the latter scenario.

I don't believe this is true. The subs are calibrated for a smooth response with the rest of the speakers. Only at the mixing desk is the sub calibrated for +10dB response so that LFE levels are recorded at -10dB vs. the other channels for the same "volume".

When calibrating speakers using the SPL meter you use tests signals for main channels at -30dB and calibrate to 75dB. With the LFE you use a -40dB signal and calibrate to 75dB. The upshot of this is that the LFE speakers are now 10dB louder than the main speakers and any signal passed to them is played 10dB louder...

Mark

Doesn't sound right to me based on what I have read in a Dolby paper. I'll read the link through again though. This stuff is so fundamental and so poorly documented.

From a Guy Kuo post:

"On occasion, you may be told that your subwoofer should be calibrated to produce an SPL which is 10 dB higher than the other channels. There is no need to do this with AVIA's subwoofer test tones because they are recorded 10 dB softer to automatically produce a 10 dB higher subwoofer setting when you target the same 85 dB SPL. If one wishes to be technically more correct, the 10 dB offset actually is only true if one is using an RTA to measure sound levels. We're using an SPL which would read about 3 dB lower for the same subwoofer setting. If you want to be completely correct, place sub level 3 dB lower at 82 dB instead of 85 dB SPL."

I use AVIA Pro and RTA for calibration, so I do use the -30dB/-40dB offsets. With SPL looks like you use 3dB difference.

I'm glad I only do this calibration very infrequently!

Mark

The implication of calibrating the sub 10dB higher for a given input suggests that:

1) When a sub is used to output re-directed bass from the other channels (e.g. mono sub with 80Hz crossover from the other speakers), this redirected bass must be reduced by 10dB or it will come out too loud.

2) Cinema does nothing. Discrete lowers the LFE channel by 10dB.

1) Yes. Bass management.

2) Yes! This agrees with the Meridian manual.

Mark