Once Again is one of those quad-to-5.1 jobs, so it's probably best to delete the center altogether.
DIGITAL At Least a Dozen 2002/2003 Elliot Scheiner 5.1 Mixes Have a LFE Issue (info/list/fixes inside)
- Thread starter steelydave
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Once Again is one of those quad-to-5.1 jobs, so it's probably best to delete the center altogether.
knifeman
500 Club - QQ All-Star
Believe it or not, I am thinking of buying one. Thanks for the warning.Buy a telescopeIt suffers from the same flaw (worse, in fact) and for the same reason. They're complex instruments, each owner configures theirs a bit differently, and there isn't enough economy of scale to foot the bill for software that "just works."
I recommend it highly! Just don't expect it to be smooth sailing all the way.Believe it or not, I am thinking of buying one. Thanks for the warning.
@steelydave, you are the only one in this whole thread who's brought up that it's the playback system's job to send the appropriate low frequency material to the subwoofers.
It's called a "Low Frequency Effect" channel, not a "Subwoofer" channel. In their wisdom, the creators of 5.1 sound knew that it needs to be the responsibility of the playback receiver to crossover music material to the subwoofer. People who mix music and movies don't know what kind of subwoofer / satellite speakers you have, and what the crossover points are. Your receiver knows. To arbitrarily have some frequency range of music in the LFE channel is just complete folly, but somehow only a few 5.1 sound mixers seem to understand this.
With the possible exception of the canons in the "1812 Overture", no one should be mixing 5.1 music with any material in the LFE channel.
It kind of looks like most of these mixes are sending the musical low frequencies to the LFE channel, but not applying a similar hi-pass filter to the rest of the channels. This means it might be appropriate to mute the LFE material, let your receiver decide what to send to the subwoofer, and boost the subwoofer volume to compensate for the junky LFE data that we blocked.
Am I crazy?
Nope, its why I don't have a LFE sub as its an effect channel, for it to work properly you should be feeling its effect! I'm not that much of a fan of the Centre either, as its really there to centre the speech in the middle of the screen in cinemas as people are sitting across a wide area. Atmos came about for the same reason but to help with surround effects placement. However, without 5.1 appearing we probably wouldn't have had music mixed into surround, and Atmos is allowing us to get new mixes, so its the rough with the smooth, but either way I'm just happy to get music in surround.
NB: I can't think of the last time I watched a film/movie in surround, in fact I can't remember when I last watched one!
I'm still working on the B's, just got to Blackfield IV (5.1 mix by Steven Wilson).
Yup, 10ms LFE delay. Maybe someone could ask him?
Yup, 10ms LFE delay. Maybe someone could ask him?
OMG! Do we have a line on Mr. Wilson here? He's my god for his Yes mixes! I would love for him to comment on why he has music program material in the effects channel in the first place. I just looked at his Blu-ray of "The Yes Album", and there's material there in the LFE channel. It looks like it's crossed over at about 200 Hz (and yes, it's about 15-18 mS delayed).
Insiders will say they did everything correctly. We are probably seeing errors in the software we use to rip and convert to flac. Sounds ludicrous but of course they will.
Why only on some titles, and mostly only LFE? I think it’s authored with the delay.
Of course it is. But the authors will claim no fault. Just watch.
Interestingly when I mentioned this delay issue to my kid who does sound design, their response was, are they sure it's not just the phase shift of the filter?[ now playing: Jethro Tull, "Wond'ring Aloud ]
OK - just what the hell is going on here, anyway?
This delay has now been demonstrated in so many titles, I've started wondering if there aren't just some natural phenomena at work here, as DuncanS humbly submitted waaay back up the road in this thread.
As we know, the LFE channel, among other treatments, is (ostensibly) a low-pass filtered extract from the main program. I understand for the most part the way filters work, and the phase shift they produce. But something with which I still struggle is the concept of group delay. I've read all the technical explanations of what it is, and they seem to make sense enough, but I'm just not able to grok the overall effect for some reason. But Duncan's reminder has stuck with me throughout my reading of this developing saga, and has made me curiouser and curiouser. So I decided to make an LFE channel of my own, from scratch, to see the exact changes that occur to the timing of the waveform.
I wanted something with a nice big convenient bassy transient right at the start, so of course I went straight to "Morph the Cat."
View attachment 64154
The full-range version is on top, the filtered version of that same waveform below. I've used the selection tool to measure the delay; it starts at a waveform peak on the full-range, and ends with the corresponding peak on the low-pass filtered version. Way down in the lower-right corner I've circled the length of the selection (delay), which is 6 milliseconds.
To satisfy my own curiosity I did another round, this time moving the cutoff to 120 Hz just to observe any changes. Here's that output:
View attachment 64155
This delay came in at 4 mS.
The 2 conclusions I'm drawing from this experiment are:
1. Allowing for rounding errors caused by the 1 mS resolution of the Cool Edit timeline, these figures line up just fine with Duncan's formula above.
2. These delays are in the general area of those being discovered by so many here, and I believe they account in large part for what we're seeing. We all know that the processing of the LFE channel can vary widely from one title to the next, from the ridiculous full-range examples to any number of unspecified LP filter treatments. There's certainly no standard being adhered to with this stuff. In my estimation, this would account for a lot of the variation in delay times being measured.
So for me, the question now becomes: Why do some titles NOT show this delay?? Perhaps they were processed in the digital domain, using FIR filters (which can be configured for no phase shift or group delay) as opposed to the more conventional IIR types, which are basically digital versions of classic analog filters, with all the attendant phase behavior? That's my guess at this point.
Any other thoughts or ideas gratefully received.
Finally - Thanks DUNCAN!
I found this article which seems to document the same issue and diagnose it as being related to the low-pass filter (LPF) and possibly the encoder. https://www.aes.org/technical/documentDownloads.cfm?docID=248
I definitely have not read it all but it seems relevant.
For instance, see Fig. 3 about which they say "In this condition, a peak-to-peak delay of approximately 8 ms is observed in the impulse response." Sounds familiar.
They show that some "encoders employ some processing to align the LFE and the mains, although they use LPF in the LFE channel" and say that "We have information that some older versions of DP569 exhibit a delay in the LFE channel when the LPF is switched on."
So maybe the culprit is the encoder.
Jim the Oldbie
My right elbow hurts.
Thanks for the link!
Yup, the delay is likely some combination of group delay and phase shift*, although admittedly that's still part of what I don't understand about it. Is group delay just a type of phase shift, or should they be thought of as separate phenomena? I need to sit in a quiet room, with a liter of coffee and a good book or 3, and figure this stuff out one of these days. Maybe some biscotti too.
* (plus maybe a bit of random digital latency weirdness just for good measure)
Yup, the delay is likely some combination of group delay and phase shift*, although admittedly that's still part of what I don't understand about it. Is group delay just a type of phase shift, or should they be thought of as separate phenomena? I need to sit in a quiet room, with a liter of coffee and a good book or 3, and figure this stuff out one of these days. Maybe some biscotti too.
* (plus maybe a bit of random digital latency weirdness just for good measure)
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I really find it interesting that so many people are going back and adjusting all these LFE channels. I'm not belittling the idea as I love making changes to surround mixes that don't sound right, but I just don't see the point in adjusting a wave diagram to "look correct" if the music/mix sounds fantastic already. For example, Beck "Sea Change" sounds amazing and has always been highly regarded by most surround enthusiasts (and myself), so what do I care if the LFE is off by a few milliseconds? For me, listening to the music is what's most important as opposed to looking at it. On the other hand, I'm sure many people here have better or more trained hearing than me, or their bass management is set up differently, so maybe making this small change yields audible rewards, and in those cases the extra work would be justified. It's very interesting the change in outlook that's occurred around QQ the last few years as more people have shifted to ripping music and looking at the wave forms. In the end, we audiophiles all seem to have a bit of OCD, so I can understand how knowing that something is off by a few milliseconds, audible or not, could decrease one's enjoyment of the music. Personally, though, a mix has to sound wrong in some way before I'll bother putting any work in.
Yes I completely agree with you, there's no point in lining up waveforms just for the sake of it. Believe me, I wouldn't have even started this thread if it was just an OCD thing.
When waveforms are out of sync by even a small amount, there's a cancellation effect which means the LFE is doing the opposite of what it should be doing, subtracting bass from the mix instead of augmenting it.
In my real-world tests, listening to corrected versions both as stereo fold-downs on headphones and on my "big system" as 5.1 there was a noticeable difference in the amount of bass content, and in a pleasing way, not just a "MORE BASS" kind of what, which is why I started this thread.
If you have a system with full range speakers and no bass management (ie speakers set to LARGE) then this thread is probably moot, but for anyone else, there is a substantial improvement in my opinion.
I also don't agree with the idea that if something sounds good or great, that there still isn't room for improvement. If that was the case, what's the point of remastering anything, or audiophile labels in general? I appreciate this thread is a downer in some ways because maybe it makes people feel like their prized possessions have been devalued in some way by me suggesting there's a flaw (which is why I went to such extensive lengths in laying out my research and methodology, I wanted this thread to be useful and informative, not a way to kind of sneer at a lot of great engineers) in them, but by the same token how can you decide that what you have is the best possible iteration of something if you haven't listened to any proposed improvements? Things can always be bettered or improved upon, and if you don't believe it, it's your own folly - itt's like the guy who ran the US Patent Office in the late 1800's who wrote to the president asking him to shut the department down because he believed everything of note had already been invented. Little did he know the industrial revolution was just around the corner!
When waveforms are out of sync by even a small amount, there's a cancellation effect which means the LFE is doing the opposite of what it should be doing, subtracting bass from the mix instead of augmenting it.
In my real-world tests, listening to corrected versions both as stereo fold-downs on headphones and on my "big system" as 5.1 there was a noticeable difference in the amount of bass content, and in a pleasing way, not just a "MORE BASS" kind of what, which is why I started this thread.
If you have a system with full range speakers and no bass management (ie speakers set to LARGE) then this thread is probably moot, but for anyone else, there is a substantial improvement in my opinion.
I also don't agree with the idea that if something sounds good or great, that there still isn't room for improvement. If that was the case, what's the point of remastering anything, or audiophile labels in general? I appreciate this thread is a downer in some ways because maybe it makes people feel like their prized possessions have been devalued in some way by me suggesting there's a flaw (which is why I went to such extensive lengths in laying out my research and methodology, I wanted this thread to be useful and informative, not a way to kind of sneer at a lot of great engineers) in them, but by the same token how can you decide that what you have is the best possible iteration of something if you haven't listened to any proposed improvements? Things can always be bettered or improved upon, and if you don't believe it, it's your own folly - itt's like the guy who ran the US Patent Office in the late 1800's who wrote to the president asking him to shut the department down because he believed everything of note had already been invented. Little did he know the industrial revolution was just around the corner!
+1,000 and coming from YOU means a lot to many of us here who have enjoyed your "renditions" of our favorite titles...one man's improvement is another man's OCD...I think you are spot on about the shift on the forum the last few years...more "experts" have surfaced...it used to bother me when new surround titles surfaced and the "honeymoon" of enjoying these treasures only lasted a day or so...but I've conditioned myself to ignore all the negativity...I just let the "experts" battle it out for attention of the masses...
Thanks for speaking up for the silent majority on here
Ugh. I dislike the use of that term in other contexts, and I'm surprised to see it used here. I guess I don't understand why this issue needs to be divisive. Those who don't care about it simply have to ignore this thread, and those who are interested in it can continue to look into it.+1,000 and coming from YOU means a lot to many of us here who have enjoyed your "renditions" of our favorite titles...one man's improvement is another man's OCD...I think you are spot on about the shift on the forum the last few years...more "experts" have surfaced...it used to bother me when new surround titles surfaced and the "honeymoon" of enjoying these treasures only lasted a day or so...but I've conditioned myself to ignore all the negativity...I just let the "experts" battle it out for attention of the masses...
Thanks for speaking up for the silent majority on here
I wasn't aware that having an opposing viewpoint was divisive...that wasn't my intention...and I usually do ignore threads like this..but I saw skherbeck's post and decided to read the thread...my mistake
While I have the capability to fix this issue on my rips, I just don't have the ambition to undertake it as yet. I too would like too hear an explanation from the pros before doing so.
I have had a quick reading to that paper and It looks like they do not provide any final solutions. Just make arise the issues to launch a debate.
I resume four points as I think I understood:
We do not have any good knowledge if or how Our AVR and SUB behaves with respect to generating phase mismatch depending on Bass Management is active or not. How can we measure that?
So, we cannot be sure if the eventually generated AVR/SUB phase mismatch would be added or cancelled to the original phase mismatch that would eventually exist in a particular source track. And if we change the original phase mismatch, we cannot know exactly the end result.
Would it be better to have more Bass or better to have less Bass for a few amount cancelled?
Complicated.
My Conclusion:
I like to follow this technical thread because you always learn something new.
With respect to change or not to change the waveform, and check if you like more or not, I think everyone should be allowed to do it. I mean that nobody should be criticised when he spends his time doing that kind of tests. For his pleasure and for us to learn about his conclusions.
What I will do? Just to enjoy the music. And if I feel there is too few Bass, just engage more the DEQ or increase the SUB gain. As it has been done for years.
But, I will keep following this thread with great interest.
I resume four points as I think I understood:
- First, I read that the best method to avoid the Bass cancellation between Mains and LFE is to add a delay in the mains to “put in phase”. This is what we have been talking in this thread all the time. BUT this is supposed to apply only to the generation of the Master File, I think.
- Then, in the section of how a Home AVR runs with Bass Management active (Speakers Small), it says that the sum of the Mains Bass redirected to SUB and the LFE channel are both passed by the same LPF and no phase cancellation occurs. But if NO bass management (Speakers Large), the LPF applied to LFE will induce the phase mismatch.
- Also more complicated things about Different AVR Bass management implementation and different SUB LPF implementation can cause different amounts of phase mismatch.
- Also interesting that It recommends NOT using any available LPF in the SUB itself as that will introduce additional phase mismatch.
We do not have any good knowledge if or how Our AVR and SUB behaves with respect to generating phase mismatch depending on Bass Management is active or not. How can we measure that?
So, we cannot be sure if the eventually generated AVR/SUB phase mismatch would be added or cancelled to the original phase mismatch that would eventually exist in a particular source track. And if we change the original phase mismatch, we cannot know exactly the end result.
Would it be better to have more Bass or better to have less Bass for a few amount cancelled?
Complicated.
My Conclusion:
I like to follow this technical thread because you always learn something new.
With respect to change or not to change the waveform, and check if you like more or not, I think everyone should be allowed to do it. I mean that nobody should be criticised when he spends his time doing that kind of tests. For his pleasure and for us to learn about his conclusions.
What I will do? Just to enjoy the music. And if I feel there is too few Bass, just engage more the DEQ or increase the SUB gain. As it has been done for years.
But, I will keep following this thread with great interest.
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