The Centre channel: what signal gets sent to it? How demanding compared to Left and Right?

[Sancus]

I work on the assumption that LFE might or might not be discarded. This means I don't want to have content duplicated in mains and LFE because it makes the downmix summing unwieldy, and if content is only in the LFE then it mustn't be mission critical.

Thanks for all that info. The above is pretty ridiculous to me. You'd think Dolby would at least be able to enforce a consistent and straightforward treatment of the LFE after like, 3 decades of dealing with it, within their own proprietary codec stack that they have complete control over... lol...

 

[Newman]

Thanks guys, it has been an interesting exploration of the topic.

There were some informative waveform plots of multichannel mixes posted on page 2. They showed how the centre channel can have (1) more energy in movies and (2) less in music, compared to front left and right.

But nobody has explored in this thread how it plays out for upmixed stereo. Has anyone looked at this? Do 1 and 2 above still apply?

cheers

 

[gene_stl]

Different upmixers use different formulae to generate the center channel. Formulae that are probably trade secrets.

 

[Sancus]

But nobody has explored in this thread how it plays out for upmixed stereo. Has anyone looked at this? Do 1 and 2 above still apply?

TLDR; I don't think the upmixing case changes any conclusions.

Listening tests with Auro3D indicate that the center never exceeds the L/R when upmixing, but of course this would vary with material. Perhaps a silent passage with only center vocals would rely mostly on the center. However, no matter what scenario you pick, the overall per-speaker load will be less than stereo because Auro3D adjusts the SPL of the L/R down to compensate for all the additional speakers playing.

I'm too lazy to test the other upmixing algorithms since I think they suck; but the only one I'd think might do more is Dolby Surround w/center spread off? But I doubt it's so aggressive that it would be worse than multi-channel music.

If you really want to be sure you could record and analyze material from the pre-outs of an upmixing AVR but, yeah, I'll pass

 

[Blumlein 88]

TLDR; I don't think the upmixing case changes any conclusions.

Listening tests with Auro3D indicate that the center never exceeds the L/R when upmixing, but of course this would vary with material. Perhaps a silent passage with only center vocals would rely mostly on the center. However, no matter what scenario you pick, the overall per-speaker load will be less than stereo because Auro3D adjusts the SPL of the L/R down to compensate for all the additional speakers playing.

I'm too lazy to test the other upmixing algorithms since I think they suck; but the only one I'd think might do more is Dolby Surround w/center spread off? But I doubt it's so aggressive that it would be worse than multi-channel music.

If you really want to be sure you could record and analyze material from the pre-outs of an upmixing AVR but, yeah, I'll pass

Same here. I could do some measurements of upmixing. I've never heard an upmixer I liked in the least. Even the old Lexicon Logic 7 wasn't good to me. I've not heard Atmos upmixes which some say are better. So I'm not much motivated to measure it. If the source is stereo I'd just play stereo.

 

[KMO]

I'm too lazy to test the other upmixing algorithms since I think they suck; but the only one I'd think might do more is Dolby Surround w/center spread off? But I doubt it's so aggressive that it would be worse than multi-channel music.

If you really want to be sure you could record and analyze material from the pre-outs of an upmixing AVR but, yeah, I'll pass

Well, all non-spread upmixes like DPL II Movie and default Dolby Surround will be maximally steering.

The upmix will look like a 5.0 film soundtrack - very centre-heavy as it puts mono signals into centre only. The intent is to reverse a 5.1->2.0 downmix as much as possible.

That's far from optimal for non-Dolby-encoded music content, hence DPL II Music and the centre spread option for DSU.

DPL II Music has a 7-step control for centre width - basically "having isolated the mono component, where should I put it?". 0 means "centre only", same as DPL II Movie, 6 means "L+R only" (so centre isn't actually used at all), and 1-5 are intermediate weightings for C vs L+R. Default is 3, basically equal L/C/R level, though I've never measured it precisely. (And the last bit of secret sauce is the C is delayed by 2ms.)

 

[Nootmuskaatje]

I guess my own take on it is that the center doesn't need to be more "muscular" than the L/R, but it needs to be just as capable in SPL terms if it's not to be limiting factor in a system.

Moreover, since it leads the way in terms of content for film, when deciding on a system (for movies only, not mixed use) I'll build from the center outward. By that I mean, when listening on demo I'll start with the center and choose the rest once I'm happy with that, rather than falling in love with stereo pair and then finding there isn't a good center to match in. It is undoubtedly the speaker that you hear the most from in a movie.

It could have some use in being more muscular. I for instance raise center volume with 3dB, which, when listening at high volumes, will mean quite the extra watts.

 

[Andysu]

In my 11 speaker HT setup I don’t use bass management. LCR can go as low as 25Hz, surrounds and ceilings as low as 60Hz. My two subwoofers are fed with LFE only without any filtering.

Same here all cinema grade JBL five screen wide behind the AT screen and tuned down to 20Hz. LFE.1 plays as is, rarely do I use the all-channel blended onto it. surrounds side/back, below surround, overheads tuned for 30Hz.

 

[Newman]

It's your choice, obviously, but LCR are not in the ideal placement for best quality bass reproduction. Surrounds and overheads even less so.

Divert bass below 80-100 Hz to 2 to 4 decent subs, that have been placed in bespoke positions for your room and listening setup, and apply EQ intelligently all the way to 200-300 Hz, and overall sound quality from music will be upgraded.

This idea, that the less music one can send to subs the better, is misguided.

 

[sarumbear]

It's your choice, obviously, but LCR are not in the ideal placement for best quality bass reproduction. Surrounds and overheads even less so.

Divert bass below 80-100 Hz to 2 to 4 decent subs, that have been placed in bespoke positions for your room and listening setup, and apply EQ intelligently all the way to 200-300 Hz, and overall sound quality from music will be upgraded.

This idea, that the less music one can send to subs the better, is misguided.

What you are suggesting has no mention in Dolby specification. How can you think that using a setup as per the specifications is not ideal? Do you mean a Dolby certified set-up is wrong?

FYI, I do not listen music on my HT. It is my home theatre, as the name says. I have a separate room where I listen music.

 

[Newman]

Hopefully your separate room where you listen to music has the kind of stuff I'm talking about.

 

[sarumbear]

Hopefully your separate room where you listen to music has the kind of stuff I'm talking about.

Nope. I have just two speakers. They go sufficiently low enough for music.

 

[Newman]

Crippleware in this day and age.

 

[sarumbear]

Crippleware in this day and age.

You have every right to think whatever you want, however I respectfully disagree. Even though it is pretty odd to think that almost all recording and mastering studios equipped with crippleware sound systems. Bass management is a solution if your speakers are not capable, or if you don't want to use acoustically treat your room, or don't use powerful EQ. It is just a cheap solution.

 

[Andysu]

JBL 4673A (rare) five screen wide. L Lc C Rc R bass-mid HF is reproduced as intended
JBL 2226 15"
JBL 2445 CD
JBL 2380A horn

 

[flyzipper]

What you are suggesting has no mention in Dolby specification.

View attachment 175196
That's from the Dolby document, "Dolby Atoms Home Entertainment Studio Technical Guidelines", published May 6 2021.

What specification were you referring to?

Admittedly, "speakers with limited low-frequency response", isn't specific, but I don't think it's unrealistic to have 20Hz-20,000Hz as a design goal, and if that's the case, the majority of speakers would be considered "limited" in their ability to deliver 20Hz with sufficient levels, so subwoofers would be required.

I have just two speakers. They go sufficiently low enough for music.

... for you.

 

[sarumbear]

View attachment 175195
View attachment 175196
That's from the Dolby document, "Dolby Atoms Home Entertainment Studio Technical Guidelines", published May 6 2021.

What specification were you referring to?

Admittedly, "speakers with limited low-frequency response", isn't specific, but I don't think it's unrealistic to have 20Hz-20,000Hz as a design goal, and if that's the case, the majority of speakers would be considered "limited" in their ability to deliver 20Hz with sufficient levels, so subwoofers would be required.


... for you.

Do please re-read. That is for the LFE channel, not through bass management, i.e. the subwoofers are fed only from the LFE channel, LCR, etc. are not send to them.

There is a section about bass management to be used if the low frequency of the speakers are limited. However, it clearly qualifies what limited means; "all speakers' response should extend from 40Hz at the low frequencies..." (2.5.2). How many small 2-way speakers you know that can go down to 40Hz? In other words contrary what you think, Dolby does not accept the use small 2-way bookshelves.

 

[sdiver68]

Here's the parameters I use when giving home audio recommendations and considering the center channel question.

1) Only the buyer cares about "perfect" sound. The rest of the friends/family are awed by impressions of volume, aesthetics, bass, etc..

2) The buyer sits at MLP

3) The buyer cares enough about great sound to be on forums researching options

4) The buyer does not have the experience to have personally auditioned thousands of gear combinations with years of quality knowledge under their belt.

5) The buyer will later spend more money upgrading..it's what enthusiasts do. Thus, I want to support the smoothest upgrade path that requires less revision to the original investment.

6) The buyer states great music is an important consideration, versus HT 100%.

7) The system exists in a living space.

For almost any given speaker budget < X which is < $5000(?) MSRP, spending that money on better L/R/LFE and using phantom center is a good option vs buying a center channel within budget.

 

[sarumbear]

Here's the parameters I use when giving home audio recommendations and considering the center channel question.

1) Only the buyer cares about "perfect" sound. The rest of the friends/family are awed by impressions of volume, aesthetics, bass, etc..

2) The buyer sits at MLP

3) The buyer cares enough about great sound to be on forums researching options

4) The buyer does not have the experience to have personally auditioned thousands of gear combinations with years of quality knowledge under their belt.

5) The buyer will later spend more money upgrading..it's what enthusiasts do. Thus, we want to support the smoothest upgrade path.

6) The buyer states great music is an important consideration, versus HT 100%.

7) The system exists in a living space.

For almost any given speaker budget < X which is < $5000(?) MSRP, spending that money on better L/R/LFE and using phantom center is usually a better choice than buying a center channel within budget.

I disagree with the above vehemently. It is not an advice to the buyer but a way for a seller to keep a connection open with a client. I think it is called a captive customer.

 

[sdiver68]

I disagree with the above vehemently. It is not an advice to the buyer but a way for a seller to keep a connection open with a client. I think it is called a captive customer.

Except Im not a seller and have no vested interest in buyer other than to help them sort through options and optimize a multi-variable decision.

Im all about the value of perspectives and fine with disagreement but attacking the motives with implied financial gain considerations is a non-starter.