Do all Mediatek-based BDPs have bass management anomalies? - AVS Forum
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post #1 of 4 Old 02-06-2012, 01:16 AM - Thread Starter
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What Paul Miller of hi-finews said here:

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Because all Oppo-based players share a common platform it’s reasonable to assume they all share the same anamolies in bass management. So the Primare, like the Cambridge 751BD, offers a drop of –5dB in LFE output relative to all main channels set to ‘Large’ with no re-distribution of centre channel output if this is set to ‘Small’ unless, oddly, the surround channels are also set to ‘Small’. Also, with the LFE/Sub channel turned off, its bass contribution does not appear to be mixed into the main channels unless one or more of them is also set to ‘Small’. The problem here is that if either centre or surround are set to ‘Small’ then the front channels can be overloaded and clip. Counter-intuitively, if both centre and surround are set to small, this does not happen.

Is this true in other current Mediatek-based players besides the CA 751 or just his assumption? I've not seen anything here or other reviews that mention it.

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post #2 of 4 Old 02-06-2012, 01:44 AM
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^ Since there are differences between the Oppo 93/95 and the Oppo 83 (e.g., in what happens to LFE when you set the Subwoofer to OFF), it's evident that his "all Oppo" players comment is, umm, not sufficiently thought out.

It also looks like he's got some basic facts wrong. The Analog Subwoofer output of the Oppo 93/95 for example is a fixed -15dB down from the Analog main speaker channels regardless whether those speakers are all set to Large or not. The first -10dB of that comes from the standard encoding of LFE. The additional -5dB allows headroom in case any of the speakers are set to Small. The fundamental document from Dolby Labs (circa 2000) defining how to do this stuff includes this as an approved method. The necessary +15dB boost should be applied external to the player. You can of course simply raise the volume knob on the sub. But typically an AVR will provide +10dB of that by default, and several AVRs offer the full +15dB as an option.

I've heard zero complaints against the Oppo players for the other problems he alludes to, and there are *LOTS* of people using the player's bass management in, for example, the Oppo 95 who are posting in its thread. He may indeed have found a bug, but I'd be very surprised if a bug like that was missed by all the enthusiasts in the 95 thread.
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post #3 of 4 Old 02-08-2012, 01:39 AM - Thread Starter
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Bob, thanks for your prompt and articulate reply as usual. The -15dB LFE is a deviation from the norm isn't it but in no way as serious as those depicted in the article.

No CA 751 users want to comment or want to admit they have a faulty player?

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post #4 of 4 Old 02-08-2012, 01:49 AM
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Quote:
Originally Posted by Kilian.ca View Post

Bob, thanks for your prompt and articulate reply as usual. The -15dB LFE is a deviation from the norm isn't it but in no way as serious as those depicted in the article.

Not really. There's more than one "approved" way of doing this. The choice is between having a fixed attenuation -- regardless of whether any speakers are set to Small, or changing the attenuation based on whether any speakers are set to Small. Both methods are spelled out in the defining document from Dolby Las that I alluded to.

Oppo feels the fixed attenuation approach is less confusing for users if they play with Large/Small settings. There's also the issue of users who want to use DSD-Direct-to-Analog conversion for SACD playback, since when that is engaged, no bass steering can happen (no audio processing of ANY sort can happen), so any speakers set to Small get treated as Large. To have the sub output change attenuation then as well is a recipe for user confusion.
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