Does LFE belong in a stereo downmix? - AVS Forum
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post #1 of 41 Old 07-21-2013, 09:58 PM - Thread Starter
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AFAIK, the LFE channel is dumped in a stereo downmix primarily to prevent damage to traditional two-channel speakers under the assumption they can't handle deep bass. But if your speakers have a crossover, is it recommended to add LFE content into the downmix?
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post #2 of 41 Old 07-22-2013, 10:45 AM
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AVRs and processors do not normally drop the LFE channel. It is mixed into the R/L channels. Source devices such as DVD/BD players generally do drop the LFE channel when downmixing LFE containing content to their R/L analog outputs.

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post #3 of 41 Old 07-22-2013, 11:31 AM
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The Dolby Guide to Metadata paper describing downmixing says its decoders drop LFE when downmixing 5.1 content for either Lt/Rt or Lo/Ro stereo output.

p12:
Quote:
In all downmixes, the LFE channel is not included.

http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/18_Metadata.Guide.pdf
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post #4 of 41 Old 07-22-2013, 11:34 AM
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Quote:
Originally Posted by BIslander View Post

The Dolby Guide to Metadata paper describing downmixing says its decoders drop LFE when downmixing 5.1 content for either Lt/Rt or Lo/Ro stereo output.

p12:
http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/18_Metadata.Guide.pdf

I am not sure if this is in response to what I posted or not, but what AVRs/processors are capable of doing in the digital realm is not technically considered "downmixing".

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post #5 of 41 Old 07-22-2013, 11:44 AM
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Yes, my post was in response to yours. And, yes, reducing the number of input channels to fewer output channels is known as downmixing. Processors do other tasks, too, of course. But, downmixing is just the process of channel reduction.

Dolby decoders use metadata to control downmixing of multichannel sources and I was simply pointing out that Dolby says it does not include LFE when downmixing 5.1 sources to stereo outputs.
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post #6 of 41 Old 07-22-2013, 05:58 PM
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Quote:
Originally Posted by BIslander View Post

The Dolby Guide to Metadata paper describing downmixing says its decoders drop LFE when downmixing 5.1 content for either Lt/Rt or Lo/Ro stereo output.

p12:
http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/18_Metadata.Guide.pdf
That paper is 8 years old...I would be interested if things have changed for bluray...the article talks about DVD only.

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post #7 of 41 Old 07-22-2013, 06:25 PM
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We're talking about downmixing multichannel sources with LFE to stereo. Is there some reason to think that there would be a reason to handle downmixing of Blu-ray different from DVD? If anything, I'd think the inclusion of LFE would be less likely on BD.

It's probably a moot issue with TrueHD, which is built on a lossless 2 channel core. So, there is no downmixing there at all. The decoder simply plays the 2 channel version and ignores the extension data that is used to create the 5.1 and 7.1 outputs.
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post #8 of 41 Old 07-22-2013, 06:31 PM
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Quote:
Originally Posted by josh6113 View Post

That paper is 8 years old...I would be interested if things have changed for bluray...the article talks about DVD only.

Nothing has changed. BD players also drop the LFE channel when downmixing LFE-containing material for 2-channel analog output.

But, just to reiterate, if LFE-containing material is passed digitally (whether that be as bitstream or multichannel PCM) from any source device to an AVR/processor for processing, there, the LFE channel will be maintained and mixed into a 2-channel "downmix".

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post #9 of 41 Old 07-22-2013, 06:35 PM
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You seem to be saying that Dolby decoders in AVRs act differently than Dolby decoders in players. I find that difficult to believe. Why do you think that's the case?
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post #10 of 41 Old 07-22-2013, 06:40 PM
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Quote:
Originally Posted by BIslander View Post

You seem to be saying that Dolby decoders in AVRs act differently than Dolby decoders in players. I find that difficult to believe. Why do you think that's the case?

Because that IS the case. I can't believe that in 2013 we (especially you, BIslander, who I have known here at this site for a while) are still discussing what an AVR does with the LFE channel. I am having the same discussion in another thread in the subwoofer subforum. AVRs have always rerouted the LFE channel into the main channels when configured as having no subwoofer connected, whether they are configured for 2.0, 3.0., 4.0, or 5.0 playback. And they have been doing this for more than a decade. Dolby stipulated that they be able to do this.

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post #11 of 41 Old 07-22-2013, 06:42 PM
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To address the OP's questions:
Quote:
Originally Posted by Megalith View Post

Does LFE belong in a stereo downmix?

IMO, yes. But Dolby engineers thought otherwise as far as source devices are concerned for (roughly) the reason you stated.

Quote:
Originally Posted by Megalith View Post

But if your speakers have a crossover, is it recommended to add LFE content into the downmix?

Not sure what you are getting at, here. What do you mean by "if your speakers have a crossover"?

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post #12 of 41 Old 07-22-2013, 06:49 PM
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I've never seem anything from Dolby specifying that sort of difference between decoders based on the device doing the decoding. Is there a tech paper about it?

Also, your earlier post singled out the performance of players when downmixing for analog stereo. Are you saying there's a different downmix performed for a stereo output using a digital connection?
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post #13 of 41 Old 07-22-2013, 06:54 PM
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Quote:
Originally Posted by BIslander View Post

I've never seem anything from Dolby specifying that sort of difference between decoders based on the device doing the decoding. Is there a tech paper about it?

Also, your earlier post singled out the performance of players when downmixing for analog stereo. Are you saying there's a different downmix performed for a stereo output using a digital connection?

As I pointed out, what happens to the LFE channel in an AVR in the digital domain is not considered downmixing per se; it's bass management.

Here ya go:
https://home.comcast.net/~schiz/DD_Guidelines.zip (7MB download)

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post #14 of 41 Old 07-22-2013, 07:07 PM
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I'm on a mobile device and will look at that zip file when I can. Is there a particular section I should examine?

Meanwhile, I have always seen bass management defined as the process of redirecting low frequencies from full range channels to a sub. I have never seen a definition like yours that says downmixing is a subset of bass management, but only if it happens in a processor, not a player.
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post #15 of 41 Old 07-22-2013, 08:27 PM
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/sigh


OK, so you won't listen to me. Fine. Would you listen to Sanjay? Roger Dressler?

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post #16 of 41 Old 07-22-2013, 09:02 PM
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Yes, I was going to suggest consulting Roger myself and I sent him a PM. Especially since I've had a chance to look through some of the files you linked. I cannot find any references to different downmix approaches for DD decoders in players and processors. Moreover, all references to downmixing for stereo specifically say LFE is discarded, not folded into the full range channels. Section 5.3.3 of the 5.1 Channel Production Guidelines seems pretty clear, for example. (Emphasis added.)
Quote:
Another benefit to using the LFE channel when carrying explosive bass signals is that smaller stereo systems may not be able to handle such high levels of deep bass without significant stress. Since the Dolby Digital downmix process discards the LFE signal, these low-frequency signals will not present any difficulty for these smaller systems. The remaining portions of the bass frequencies delivered by the main channels will convey the essential aspects of the performance when listening to the downmix.

I must say you seem to have quite an attitude about this - insisting not only that your view is correct, but that it is so obviously correct that anyone questioning your view is clearly uninformed. All I have I done is point to Dolby documents saying LFE is discarded when downmixing to stereo. When I asked if there were other documents supporting your position, you posted a set of documents that seem to confirm that LFE is, in fact, discarded. Am I missing something here?

PS: I looked at the thread you mentioned in the subwoofer forum. That's about redirecting LFE in multichannel systems configured without a sub, which is different from this discussion about downmixing for a stereo output.
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post #17 of 41 Old 07-22-2013, 10:12 PM
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Quote:
Originally Posted by BIslander View Post

I must say you seem to have quite an attitude about this - insisting not only that your view is correct, but that it is so obviously correct that anyone questioning your view is clearly uninformed.

Yeah, it's exasperating, Anyone questioning it IS uninformed. It's not my view, it is fact. Frankly, I am baffled that YOU would think otherwise as this is really, really "old hat" around here. It is one of the most fundamental tenets of bass management.

Apparently, you entered this thread to specifically dispute my response to the OP. Right?

Quote:
Originally Posted by BIslander View Post

PS: I looked at the thread you mentioned in the subwoofer forum. That's about redirecting LFE in multichannel systems configured without a sub, which is different from this discussion about downmixing for a stereo output.

Nice backpedal (or something). I think I have already been VERY clear in this thread at the distinction that you are now trying to make. Look back at my posts. I covered my butt.


From the paper entitled "5.1-Channel Production Guidelines":
Quote:
2.4 Bass Management
Bass management allows the user to redirect low-frequency information from any of
the five main speakers to the subwoofer; conversely, if there is no subwoofer, the
LFE information can be redirected to the left and right speakers.

An AVR will ALWAYS reroute the LFE channel (when present, of course) to the main channels when configured as having no subwoofer; be it configured for 2.0 playback or 7.0 playback - it doesn't matter.

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post #18 of 41 Old 07-22-2013, 10:16 PM
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Finally, you've quoted something from Dolby. But, it's relevant to your other thread, not this one, describing what happens to LFE in a multichannel system configured without a sub. Here's the quote, including the next line, showing the context is systems with five full range speakers:
Quote:
Bass management allows the user to redirect low-frequency information from any of the five main speakers to the subwoofer; conversely, if there is no subwoofer, the LFE information can be redirected to the left and right speakers. This is important as the vast majority of consumer home theater speaker systems require some degree of bass management since typically none of the five main speakers is designed to reproduce frequencies below 80 Hz (i.e., satellite/sub speaker arrangements).

Is there a reason you continue to ignore all of the seemingly clear, unambiguous statements in the Dolby papers saying its decoder discards LFE when downmixing to stereo? Why do you suppose those statements are in the Dolby metadata and production guides if that is not what happens? (If you respond to any part if this post, please start here, since my position is based solely on what Dolby says it is doing when downmixing to stereo.)

And, no back-pedaling on my part at all. The title of this thread specifies downmixing to stereo. And each and everyone of my posts has clearly been about what Dolby says it does with LFE when downmixing to stereo. You are the one participating in similar, but not identical, discussions in two different threads.
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post #19 of 41 Old 07-22-2013, 10:46 PM
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Quote:
Originally Posted by BIslander View Post

Finally, you've quoted something from Dolby. But, it's relevant to your other thread, not this one, describing what happens to LFE in a multichannel system configured without a sub. Is there a reason you continue to ignore all of the seemingly clear, unambiguous statements in the Dolby papers saying its decoder discards LFE when downmixing to stereo? Why do you suppose those statements are in the Dolby metadata and production guides if that is not what happens?

I entered the thread in an effort to clarify something that the OP might not be clear about. You entered the thread, apparently, to specifically dispute that response. And what you posted in the 3rd post is irrelevant to the point I was making. That being that AVRs do NOT discard the LFE channel when "downmixing" multichannel, LFE-containing content to stereo. They don't. We (or you) can quibble about whether that is technically downmixing or not (something I already tried to clarify in my posts), but it's a moot point, AFAIC. AVRs do not discard the LFE channel.

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post #20 of 41 Old 07-22-2013, 10:56 PM
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And still you ignore the fact that Dolby says its decoder discards LFE in both types of stereo downmixing - Lt/Rt and Lo/Ro. That's the only point I have ever tried to make.

So, what happens when someone bitstreams a DD 5.1 track to a processor configured with just L/R and no sub? Are you saying the Dolby decoder will downmix to stereo while folding LFE into the stereo output? If so, why do the Dolby documents say LFE is discarded? Or, are you saying the decoder outputs the full 5.1 and leaves the downmixing up to whatever the processor wants to do? Or, something else, maybe?
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post #21 of 41 Old 07-22-2013, 11:01 PM
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Maybe I should have just said in response to your first post in this thread, "OK. So? What's your point?". How would you have responded to that?

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post #22 of 41 Old 07-22-2013, 11:27 PM
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Quote:
Originally Posted by BIslander View Post

And still you ignore the fact that Dolby says its decoder discards LFE in both types of stereo downmixing - Lt/Rt and Lo/Ro. That's the only point I have ever tried to make.

So, what happens when someone bitstreams a DD 5.1 track to a processor configured with just L/R and no sub? Are you saying the Dolby decoder will downmix to stereo while folding LFE into the stereo output? If so, why do the Dolby documents say LFE is discarded? Or, are you saying the decoder outputs the full 5.1 and leaves the downmixing up to whatever the processor wants to do? Or, something else, maybe?

Not knowing for certain, I'll stick my neck out (yes, I could be wrong, here) and say that AVRs do not use that metadata at all because they do not, technically, "downmix to stereo". They redirect non-present speaker channel info.

When someone bitstreams DD5.1 to an AVR configured as having only 2 speakers connected, all 6 channels of info, including the LFE channel, are reproduced by the R/L speakers. If you think the LFE channel would be discarded in this instance, you're wrong.



BTW, Roger Dressler has addressed the apparent difference between the Dolby decoder specifications and what AVRs actually do, before, here in these forums. I couldn't find it (trust me, I tried!) but I do remember it.

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post #23 of 41 Old 07-22-2013, 11:42 PM
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Ah, so you are saying Dolby doesn't do a downmix at all. The decoder just outputs the full 5.1 PCM and leaves it up to the processor to do any downmixing. Is there something in the Dolby tech papers about that? I've not seen anything of that nature. I'm not saying it doesn't happen that way, although I have my doubts. But, I've never seen such a description.

On a careful re-read of your last post, you don't actually go so far as to say the decoder doesn't do the downmixing. So, please clarify what you mean. Does the Dolby decoder output the full 5.1 PCM track when operating on a receiver configured as 2.0, leaving the downmixing up to the receiver?

Hopefully, Roger will respond to my PM and weigh in here.
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post #24 of 41 Old 07-23-2013, 12:09 AM
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From the same "5.1-Channel Production Guidelines":

(emphasis added)
Quote:
5.3.3 LFE Channel

What is the difference between the LFE channel and the subwoofer signal? The LFE
channel is a separate, limited frequency bandwidth signal created by the mixing
engineer and delivered alongside the main channels in the mix.

The subwoofer signal is created in the decoder as needed for the particular speaker
complement in use, using crossover filters. This signal is created using bass
management, and all Dolby Digital decoders perform this function. Through bass
management, a subwoofer signal may comprise bass from any channel or
combination of channelstypically bass frequencies from channels being replayed
on small speakers are directed to the subwoofer speaker. If no subwoofer is present,
the bass (including the LFE channel, if it exists) is redirected to the speaker(s) best
able to reproduce it, usually the main stereo pair.


Even though an eighth-order, 120-Hz brickwall filter can be applied to the LFE
channel by a Dolby Digital encoder, a low-pass filter must be inserted into the LFE
signal path during the mix process to ensure proper monitoring. Furthermore, the
filter must be applied to the signal being recorded so that the results will be
consistent, whether delivered by Dolby Digital or Linear PCM. A maximum cutoff of
80 Hz is suggested when using a typical filter with a gradual slope as compared to the
steep, low-pass filter in a Dolby Digital encoder.

In theatres, the LFE channel is used in conjunction with subwoofers to supplement
the capabilities of the screen speakers. In most music productions, it is unlikely there
will be a technical need to use the LFE channel. Since the overall program level may
be adjusted to render any proportion of bass perfectly, the LFE channel might be an
advantage only in situations similar to the famous cannon shots in Tchaikovskyís
1812 Overture. In such a case, the overall program level might have to be reduced
several dB just so the last few minutes can make the desired impact without overload.
By using the LFE channel, the orchestra can be recorded at a normal level, with some
of the loudest, deepest bass of the cannons carried in the LFE channel. Of course, the
main channels will still carry the cannon shots so that they will be heard from the
appropriate locations and in a downmix.

Another benefit to using the LFE channel when carrying explosive bass signals is that
smaller stereo systems may not be able to handle such high levels of deep bass without
significant stress. Since the Dolby Digital downmix process discards the LFE signal,
these low-frequency signals will not present any difficulty for these smaller systems.

The remaining portions of the bass frequencies delivered by the main channels will
convey the essential aspects of the performance when listening to the downmix.

While it may be of no particular consequence for effects, filters like those used in
generating the LFE signal may interfere with the ability to seamlessly blend the LFE
channel with the other channels. The best way to ensure a cohesive audio signal across
the entire audible spectrum is to maintain its integrity in the main channel(s).


So, how do you reconcile that apparent discrepancy? Is the LFE channel discarded by an AVR configured as having no subwoofer connected or not? It's not. Multichannel AVRs do not downmix, even when configured for 2.0 playback. Not the way that a source device downmixes to stereo according to the included metadata, anyway.


But, regardless of the specifics, I would challenge you to refute what I posted in my initial response to the OP. wink.gif


If you own the AVIA calibration DVD you can test how your AVR behaves, yourself, using the track entitled "Low Frequency Sweep, LFE". This is a sweep that is encoded entirely in the LFE channel. Configure your AVR for 2.0 and play that track. You will hear it from your speakers.

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post #25 of 41 Old 07-23-2013, 07:12 AM
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Quote:
Originally Posted by sivadselim View Post

Not knowing for certain, I'll stick my neck out (yes, I could be wrong, here) and say that AVRs do not use that metadata at all because they do not, technically, "downmix to stereo". They redirect non-present speaker channel info.

When someone bitstreams DD5.1 to an AVR configured as having only 2 speakers connected, all 6 channels of info, including the LFE channel, are reproduced by the R/L speakers. If you think the LFE channel would be discarded in this instance, you're wrong.



BTW, Roger Dressler has addressed the apparent difference between the Dolby decoder specifications and what AVRs actually do, before, here in these forums. I couldn't find it (trust me, I tried!) but I do remember it.

I guess you'd have to explain how redirecting the sound for speakers you don't have to stereo is not downmixing. An AVR may not use metadata from the original source to decide what levels to put the center surrounds and LFE into a two channel mix, but they sure as shootin' mix those sounds back into the 2 channel output which, to my mind, defines downmixing.

I also remember the discussionoabout this, must have been a couple of years ago at least, and had forgotten Roger provided the input that let me stop worrying about whether an AVR simply discards the LFE . . .
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post #26 of 41 Old 07-23-2013, 10:02 AM
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Quote:
Originally Posted by JHAz View Post

I guess you'd have to explain how redirecting the sound for speakers you don't have to stereo is not downmixing.

Who? Me? I don't think I have to explain anything. I stand by what I posted in Post#2, which was not at all meant to be argumentative. It was a simple post. An AVR configured for 2.0 playback will not drop the LFE channel from LFE-channel-containing content. Without knowing exactly where the OP was coming from or going to with his initial post, I just wanted to make sure he was aware of this. It was strictly for clarification and that is all.

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post #27 of 41 Old 07-23-2013, 11:21 AM
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Quote:
Originally Posted by sivadselim View Post

So, how do you reconcile that apparent discrepancy?
I am going to make an assumption that both statements are correct, which seems like a reasonable starting point given that the documents come from Dolby engineering and have been vetted over many years.

So, what would explain the seeming inconsistency? The most obvious answer is that Dolby treats stereo downmixing as a special case. In multichannel systems, the Dolby decoder redistributes all source channels, including LFE, to the channels that are configured for playback. However, when the playback system is just stereo, the Dolby decoder discards LFE to avoid the risk of what it calls "significant stress".

Do you have some other explanation that allows both statements in the Dolby document to be correct? Or, are you taking the position that the one about stereo is wrong or that it only applies to the limited case of downmixing in a device like a player or a set top box for analog stereo output? The analog stereo limitation is not an unreasonable position to take. But, surely it's sourced somewhere, yes?

I view these discussions as an opportunity to learn, which only happens with a rather rigorous examination of the issues. I come into this one believing that the Dolby decoder handles the downmix before outputting PCM to the receiver for subsequent processing and the DAC. You'll note that the passage you quoted from the Dolby Guidelines says the subwoofer signal is produced "in the decoder" and that "all Dolby Digital decoders perform this function" (bass management). Your view seems to suggest something different, that the Dolby decoder outputs the full 5.1 or 7.1 PCM, leaving it up to software in the processor to handle downmixing and bass management. I say that "seems" to be your view because I'm not really sure. I asked for your view on that in previous posts and got no answer. As for DTS, I believe its HD decoder also handles downmixing and channel expansion before outputting the resulting PCM to a receiver for subsequent processing. That belief is based on DTS' stated desire to have the output of its decoder match the number of channels configured in the playback system. That's the basis for DTS-HD Speaker Re-mapping along with the channel expansion done by DTS-HD Essential player decoders and receiver decoders such as some recent models of Onkyos. So, we are left with some questions about which software is responsible for what. You repeatedly describe what the AVR does. That would certainly apply to multichannel PCM sources, which is a rather small subset of all potential sources. What about mutlichannel Dolby and DTS sources? Do those decoders handle the downmixing and bass management before the PCM gets to the AVR?
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If you own the AVIA calibration DVD you can test how your AVR behaves, yourself, using the track entitled "Low Frequency Sweep, LFE". This is a sweep that is encoded entirely in the LFE channel. Configure your AVR for 2.0 and play that track. You will hear it from your speakers.
Yes, I do, and I've used the sweeps on the full range channels to fine tune bass management crossovers. I will take some time, likely over the weekend, to run the tests you suggest. However, I suspect it will not be relevant to the issue I have been posting about, which is whether a Dolby decoder discards LFE when downmixing for a pure stereo output. Wouldn't the LFE sweep would need to be encoded as DD 5.1 in order to test the output of a Dolby decoder?
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post #28 of 41 Old 07-23-2013, 01:07 PM
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BTW, Roger Dressler has addressed the apparent difference between the Dolby decoder specifications and what AVRs actually do, before, here in these forums. I couldn't find it (trust me, I tried!) but I do remember it.
Let me see if I can recount the facts. First, we need to distinguish between downmixing and downmixing. One of them is a process conducted within the confines of the Dolby decoder algorithm, the other happens somewhere downstream.

When 2.0 downmixing is done in a Dolby Digital decoder, the LFE is omitted. For all other cases, including other Dolby decoders like DD+ and TrueHD, LFE is not discarded.

Bass management (redirecting bass) and speaker management (redirecting channels) all occur downstream of the decoder, and only function in a multi-channel environment (no downmixing in the audio codec). So it's a totally different paradigm than the case where a 2-ch source product like a DVD player or STB outputs only 2-ch audio.

When an AVR receives a DD bitstream, and the AVR is set to stereo mode (like for headphones or plain stereo listening), there is no downmixing in the audio codec. It outputs the full 5.1 of the source, and a secondary bass/speaker management process handles the formulation of the speaker feed signals.

Let me know if this fails to clarify the situation.
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post #29 of 41 Old 07-23-2013, 02:10 PM
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Originally Posted by BIslander View Post

I am going to make an assumption that both statements are correct, which seems like a reasonable starting point given that the documents come from Dolby engineering and have been vetted over many years.

So, what would explain the seeming inconsistency? The most obvious answer is that Dolby treats stereo downmixing as a special case. In multichannel systems, the Dolby decoder redistributes all source channels, including LFE, to the channels that are configured for playback. However, when the playback system is just stereo, the Dolby decoder discards LFE to avoid the risk of what it calls "significant stress".

Do you have some other explanation that allows both statements in the Dolby document to be correct? Or, are you taking the position that the one about stereo is wrong or that it only applies to the limited case of downmixing in a device like a player or a set top box for analog stereo output? The analog stereo limitation is not an unreasonable position to take. But, surely it's sourced somewhere, yes?

I would simply take the position that when an AVR is configured for 2.0 playback, there is never an actual "downmix to stereo" involved when decoding and redirecting multichannel material. Obviously, as often as it is repeated throughout the Dolby documents, a decoder WILL discard the LFE channel when a "downmix to stereo" is performed. But since an AVR doesn't behave this way I can only conclude that there is not a "downmix to stereo" involved.


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Originally Posted by BIslander View Post

I come into this one believing that the Dolby decoder handles the downmix before outputting PCM to the receiver for subsequent processing and the DAC.

Why? I am not sure what you are saying, here. Do you mean before a source device outputs "downmixed" 2-channel PCM to an AVR? I don't know what is output in that instance but it is certainly testable. I would not be surprised at all to find that the LFE channel is dropped in this instance. It would make sense for a source device that is simply connected to a television via an HDMI connection, for example. And it would only tend to support what I posted in Post#2. That being that source devices drop the LFE channel. True, I was referring to what happens when downmixing for 2-channel analog output because I suspected that if the OP was decoding his material at his source device, he would probably be utilizing an analog connection. But I also left the possibilty open that there was a digital connection to an AVR configured for 2.0 playback, and multichannel PCM or bitstream might be being passed from the source device. Which was the whole point of Post#2. An AVR configured that way would not drop the LFE channel.

If 2-channel PCM is being passed, though, there is no LFE channel to be dropped by the AVR. It would have either 1) already been dropped or 2) mixed into the R/L channels by the source device. Either way, there is no LFE channel there to be dropped by the AVR. So it is a moot point. But I would suspect that the OP is not passing 2-channel PCM from his source device. With speakers other than the television's involved, if there is a digital connection being utilized, I would think that in most cases multichannel PCM or a bitstream is what is being passed to an AVR/processor; not 2-channel PCM.

But, again, it is irrelevant to what I was trying to clarify, that being that AVRs do not drop the LFE channel, regardless of how that LFE-channel containing material gets to the AVR.

Again, if you are passing 2-channel PCM, there is no LFE channel, anyway.

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Your view seems to suggest something different, that the Dolby decoder outputs the full 5.1 or 7.1 PCM, leaving it up to software in the processor to handle downmixing and bass management.

Yes, if you pass multichannel PCM (or bitstreamed, for that matter) material to an AVR, the LFE channel will still be maintained and routed into the R/L channels if the AVR is configured as having no subwoofer connected. But, again, I am not sure what you are saying here. Or why this is "my view". It is, frankly, irrelevant to what I posted in Post#2. That being that an AVR does not drop the LFE channel when configured as having no subwoofer connected. I really do not care "why?", exactly. When you first posted in Post#3, I wasn't sure what point you were trying to make, but it soon became apparent that you do not (or DID not) believe this to be true and had posted the Dolby paper linked in your Post#3 in order to support that.

If a player has multichannel analog outputs and can be configured for bass management, I believe that in most cases these bass management settings would only be applied to the player's analog outputs, not to the players multichannel PCM output. I think there might have been an instance or two a few years back where this was not the case and a player could actually (undesirably, I would add) pass bass-managed multichannel PCM. But I do not think that there are any bass (or time) management settings available in a player with no multichannel analog outputs. If configured to do so, the player simply passes full-range channels of multichannel PCM to the AVR/processor for processing, which includes the bass and time management.

If a player is configured to pass 2-channel PCM, again, obviously, there is no LFE channel involved at that point. The LFE channel material has either already been discarded or mixed into the other (usually the R/L) channels.


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Originally Posted by BIslander View Post

You repeatedly describe what the AVR does. That would certainly apply to multichannel PCM sources, which is a rather small subset of all potential sources. What about mutlichannel Dolby and DTS sources? Do those decoders handle the downmixing and bass management before the PCM gets to the AVR?

What do you mean by "multichannel Dolby and DTS sources"? Bitstream? Multichannel PCM? What? The LFE channel would be treated the same way by an AVR configured as having no subwoofer connected whether it is receiving multichannel PCM or bitstreamed LFE-containing material.

Again, I am not sure what you are asking/saying, here. Or why you think that passing multichannel PCM to an AVR is such a small subset. I would think that passing 2-channel PCM to an AVR would be the smaller subset. Passing multichannel PCM or bitstreamed x.1 material would probably both be much more common than passing 2-channel PCM to an AVR/processor. And whether you are passing multichannel PCM or bitstreamed x.1 material to an AVR, the LFE channel is maintained when the AVR is configured as having no subwoofer connected. This is true whether it is configured for 2.0 or 7.0 playback; it doesn't matter.


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Originally Posted by BIslander View Post

However, I suspect it will not be relevant to the issue I have been posting about, which is whether a Dolby decoder discards LFE when downmixing for a pure stereo output.

confused.gif Really? Why would it not be relevant? Having a way to discern exactly what happens to material encoded specifically in the the LFE channel in different configurations would be entirely relevant, no?


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Originally Posted by BIslander View Post

Wouldn't the LFE sweep would need to be encoded as DD 5.1 in order to test the output of a Dolby decoder?

confused.gif It IS encoded as DD5.1. There is nothing encoded in the other channels. There is only the sweep that is encoded in the LFE channel in that particular track. The sweep starts well into the range where most speakers will reproduce it (100Hz, IIRC) and descends from there.

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post #30 of 41 Old 07-23-2013, 02:11 PM
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Let me know if this fails to clarify the situation.

Clarified it just fine for me. Thanks. smile.gif

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