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Burn-in: Real Or Imagined??? - Page 15

post #421 of 665
Quote:
Originally Posted by AndreYew View Post

Ooh. This one is controversial. Floyd Toole poo-poos the idea (of multichannel bass) in his book.

--Andre

Andre - Your head interferes with the volume velocity in the room, right, and in doing so, creates pressure, eh?

Now, first, try this.

Take a 50 Hz sine wave. Play it to both ears. in phones. Play it to both ears, but invert one channel by 180.

Now, do you hear localization? No. Do you hear spatial effects? Well, most people seem to say "yes". If so, we have relevance to the human organism established. N.B. do not use high levels, or you may be able to hear the distortion spectra being different and we prove nothing.

Below 40 Hz or so this doesn't seem to be true.

Now, what does it mean if you're right at traverse zeroin a concert hall?

What does it mean when your head interferes with the energy in the traverse zero?

While it's true that the PRESSURE isn't there, the volume velocity, by definition, is. And there is pressure (out of phase) on the two sides of the zero, too.
post #422 of 665
Quote:
Originally Posted by jj_0001 View Post

Andre - Your head interferes with the volume velocity in the room, right, and in doing so, creates pressure, eh?

JJ, I'm in your camp here, and I've done the 50 Hz sine wave headphone experiment as well. I was just trying to add some fuel to the fire.

krabapple, Toole does advocate multiple subs, but all playing back the same signal in order to mitigate room modes. JJ and I are talking about different subs playing back different signals in order to reproduce a perceptual cue. Toole is pretty adamant that the latter is not useful.

--Andre
post #423 of 665
Quote:
Originally Posted by AndreYew View Post

JJ, I'm in your camp here, and I've done the 50 Hz sine wave headphone experiment as well. I was just trying to add some fuel to the fire.

krabapple, Toole does advocate multiple subs, but all playing back the same signal in order to mitigate room modes. JJ and I are talking about different subs playing back different signals in order to reproduce a perceptual cue. Toole is pretty adamant that the latter is not useful.

--Andre

I agree with Floyd. I've read most of the papers on spatial bass, and personally know most of the authors who wrote them. None of them have been able duplicate the effect using loudspeakers (not headphones) in my listening lab. In order to hear it, I'm told it takes years of training, a special type of room, and only works on certain types of recordings. It works better if you are coached and told you are hearing it... I'll take 4 subwoofers, and really smooth bass over a wide seating area any day, over an effect that is as subtle as interconnects and audible only on certain leap years.
post #424 of 665
It's the Clash Of The Objectivists! I'll pop popcorn. Oh, wait, you're basically done? Rats!
post #425 of 665
Quote:
Originally Posted by Tonmeister2008 View Post

I think the industry needs to move into this century and develop more meaningful specifications that tell a consumer how the speaker sounds.

That's a great idea. And highly unlikely. The incentive structure in the industry as far as I can see does not induce fair and equal published self-assessment. If we can't even agree if amplifiers have a sonic signature, and how to characterize it, and the FTC can't even get power tightly defined, how can that be expected of something as complex as a speaker?

let me ask you - Do you think Harman, Paradigm and PSB could agree on a recommended set of metrics for mutual assessment and publish them? (and these are the direct inheritors of the NRC lineage)

A different question might be: if you had to recommend to the reviewing industry a standard for assessment, what would it be? I can think of at least two magazines who might follow, one of which has in the past used NRC labs for article testing purposes. Could you get an partial industry/AES consensus on how reviewers should assess speakers for consumers and specific metrics to publish?

Here is another question: in the usual graphs that magazines who actually test publish, is there a way for us consumers to figure it out given the data? What data do we need? How do I assess the measured review of Paradigm vs. Harman vs PSB speakers as a consumer? What data do I need and what do I need to look for in it?

(PS didn't realize Dr. Toole had retired. That's a loss... hopefully he will enjoy consulting even more than staff work...)
post #426 of 665
Quote:
Originally Posted by Tonmeister2008 View Post

I agree with Floyd. I've read most of the papers on spatial bass, and personally know most of the authors who wrote them. None of them have been able duplicate the effect using loudspeakers (not headphones) in my listening lab. In order to hear it, I'm told it takes years of training, a special type of room, and only works on certain types of recordings. It works better if you are coached and told you are hearing it... I'll take 4 subwoofers, and really smooth bass over a wide seating area any day, over an effect that is as subtle as interconnects and audible only on certain leap years.

Actually, it's easy to show with the right recording, in 2 channel vs. 5 channel, it's not tough.

Problem is, most recordings don't capture the information you need in the first place (i.e. monoed bass or coincident mikes).

It's that simple.

JJ
post #427 of 665
Quote:
Originally Posted by jj_0001 View Post

And creating the same impression of bass that you get in a large venue with one subwoofer in a small venue can be downright (literally) impossible, too.

I'll say that having a sub is better than nothing, but no more.

I agree, multiple subs are pretty much a must IMO. Well, finally read through and see this is getting more serious than just multiple subs.
post #428 of 665
Quote:
Originally Posted by Michael Grant View Post

It's the Clash Of The Objectivists! I'll pop popcorn. Oh, wait, you're basically done? Rats!

I know you were joking, but I think this disagreement points out that there are lots of real, interesting problems left to be solved in audio, and I think it's a damned shame that the popular audio press is always obsessed with second order effects that may have not audible consequences at all --- just look at the high proportion of cables and other similar things in Stereophile's CES report this year.

It's a stereotype that objectivists only measure and that the world is black and white in that camp. There are lots of really interesting problems in audio that if solved would benefit a lot of people, but for some reason many audiophiles go on about power cords and wooden disks.

--Andre
post #429 of 665
Quote:
Originally Posted by Randybes View Post

I agree, multiple subs are pretty much a must IMO.

And the proper signals to drive them. The bass must be decorrelated to 40 Hz. Most commercially available recordings have mono (ie. perfect correlation) bass, unfortunately.

--Andre
post #430 of 665
Quote:
Originally Posted by AndreYew View Post

And the proper signals to drive them. The bass must be decorrelated to 40 Hz. Most commercially available recordings have mono (ie. perfect correlation) bass, unfortunately.

--Andre

I have also sent an invite to Earl Geddes to participate. He has some different ideas on setting up multiple subs but don't know his view on "stereo" bass.
post #431 of 665
Hey Sean, it's great to see you here! Your contributions will be a very welcome addition.
post #432 of 665
Quote:
Originally Posted by Randybes View Post

I have also sent an invite to Earl Geddes to participate. He has some different ideas on setting up multiple subs but don't know his view on "stereo" bass.

Excellent, I sent an invite to Geddy Lee, the preeminent bassist from Rush, to participate...

post #433 of 665
Quote:
Originally Posted by QueueCumber View Post

Excellent, I sent an invite to Geddy Lee to participate...


Good one
post #434 of 665
Quote:
Originally Posted by Randybes View Post

Good one

I couldn't resist the play on names...
post #435 of 665
Quote:
Originally Posted by AndreYew View Post

And the proper signals to drive them. The bass must be decorrelated to 40 Hz. Most commercially available recordings have mono (ie. perfect correlation) bass, unfortunately.

--Andre

This is indeed true. With monoed bass you achieve nothing meaningful.

Bass in any large listening room is, however, nothing near correlated as you expect, per measurements made and published, among other places, in Kuo, S. and Johnston, J. D., A study of why cross channel prediction is not applicable to perceptual audio coding, 111 AES Convention, New York, NY, 21-24 September 2001.

While that is not definitive, it shows the degree of decorrelation using part-velocity, part-pressure mikes in a near coincident array, even into bass frequencies. This shows that what hits your ear in the ORIGINAL venue is not correlated. THAT, coupled with the out-of-phase demonstration, is pretty conclusive, really.

Now, artificial stuff, say using a hilbert on bass (an interesting proposition, that, too ), may not do what you want or expect. What you want is a time characteristic much like some set of points in the original venue, not mono bass, not mono bass that's been processed.

The argument "only under special circumstances, etc" is simply not true.

We had a very nice demo at AT&T before it shut most of itself down, in which 1 and 2 channel renderings of a playback (taken from an array mike) were very, very boomy. Note, even 2 channel with 2 woofers was boomy. The 5-channel rendition, on the other hand, puts the room to the sides and back, and the boom hangs in the back like one expects, and sounds like a good concert hall rather than boomity-boom. This was with a set of 1 to 10 full range (Snell C-v) loudspeakers.

There was no sub in this setup at all.

As for the boominess, in fact the listener was getting the same average spectrum at each ear in both 2 and 5 channel, to a very notable degree. (there were some minor cancellations in mono in the bass)
post #436 of 665
Quote:
Originally Posted by AndreYew View Post

And the proper signals to drive them. The bass must be decorrelated to 40 Hz. Most commercially available recordings have mono (ie. perfect correlation) bass, unfortunately.

--Andre

Randy, with proper permissions, etc, it is most likely that I can offer a mike array for recording. I can't guarantee it, but it's likely that an array can be made temporarily available.

This, of course, an array that does show the intended effects, not a focused or coincident array.
post #437 of 665
Pardon me for getting involved without having read the entire chain, but a few questions might get me caught up.

What is meant by "decorrelated to 40 Hz."? Do you mean down to 40 Hz or 40 Hz and down?

I did a math analysis of the best possible signal processing for smoothing out bass in a small room. What I came up with turned out to actually have a name - it was called a "decorrelation filter". What small rooms lack at LFs is decorrelation. Large rooms have this by virtue of the multiple modes (high modal density). Small rooms only have a few modes and the signals thus tend to be highy correlated. If you try and add modes to a small room via some sort of electronic scheme you end up with a filter that can be seen to be a "decorrelation filter". Short of creating one of those however, exciting as many modes as possible in as smooth a sense as possible - via multiple subs and some sort of processing - achieves a very good facsimaly of a pure decorrelation filter.

A reverb unit is basically a decorrelation filter and I have often hypothesized that a reverb unit for only the subs would be an effective means of decorrelating the subs.
post #438 of 665
post #439 of 665
Quote:
Originally Posted by jj_0001 View Post

Actually, it's easy to show with the right recording, in 2 channel vs. 5 channel, it's not tough.

Problem is, most recordings don't capture the information you need in the first place (i.e. monoed bass or coincident mikes).

It's that simple.

JJ

So you admit that in order to hear the spatial effect requires recordings with non-mono decorrelated bass. That is my point. I suspect that less than 2-4% of commercial recordings (mostly classical ones made with spaced omni's & non-coincident mic techniques) meet this criterion. I would call those "special circumstances." Even under carefully controlled experimental conditions using artificial signals where the stereo bass was intentionally decorrelated (r = -1), the effect was near threshold (see Todd Welti's 2004 AES paper ).

I wish you good luck in trying to change how the recording industry makes recordings. Mono compatibility is still very important in the film and broadcast industries so they are not likely to subscribe to this. And the music industry - well, they are still trapped in mostly a 2-channel world, and barely surviving at that. Better you spend your time and effort convincing them about the spatial benefits of multichannel versus 2-channel since the spatial benefits are well above the audible threshold on 100% of the recordings -- not 2-4%.

And good luck getting consumers to use 2 or 5 full range speakers to hear spatial bass in the <2% of recordings that have decorrelated bass. Have you been to a CEDIA show lately? The speakers are small, thin or go into walls, and are connected to bass managed subwoofers. Commercially speaking, spatial bass is a non-starter.

I'm going to throw Todd Welti in the ring tomorrow for a few rounds of spatial bass battery. Start up those popcorn machines now since the fight has just begun
post #440 of 665
Quote:
Originally Posted by Bob Lee (QSC) View Post

Hey Sean, it's great to see you here! Your contributions will be a very welcome addition.

Thanks Bob!
post #441 of 665
Quote:
Originally Posted by Tonmeister2008 View Post

So you admit that in order to hear the spatial effect requires recordings with non-mono decorrelated bass. That is my point. I suspect that less than 2-4% of commercial recordings (mostly classical ones made with spaced omni's & non-coincident mic techniques) meet this criterion.

Yes, Sean, I admit that most recordings are made wrong. And? This is a reason to just leave it be as it is, or should maybe we teach people how to do it better?

Or do we just settle for monophonic bass, and stereo 5-channel (MPEG-Surround), discard all time cues, and wait for the way people percieve sound in nature to evolve away?

Same goes for non-delay panpots. We don't need mono compatability any more, but we still use panpots and create a bad front soundstage. Do we then use parametric stereo coders that require panpots in order to work right, and just give up on what we can actually hear, and let the industry drift farther and farther into mediocracy, or do we teach people how to do things that were understood before 1950?

Really?
post #442 of 665
Quote:
Originally Posted by gedlee View Post

Pardon me for getting involved without having read the entire chain, but a few questions might get me caught up.

What is meant by "decorrelated to 40 Hz."? Do you mean down to 40 Hz or 40 Hz and down?

I did a math analysis of the best possible signal processing for smoothing out bass in a small room. What I came up with turned out to actually have a name - it was called a "decorrelation filter". What small rooms lack at LFs is decorrelation. Large rooms have this by virtue of the multiple modes (high modal density). Small rooms only have a few modes and the signals thus tend to be highy correlated. If you try and add modes to a small room via some sort of electronic scheme you end up with a filter that can be seen to be a "decorrelation filter". Short of creating one of those however, exciting as many modes as possible in as smooth a sense as possible - via multiple subs and some sort of processing - achieves a very good facsimaly of a pure decorrelation filter.

A reverb unit is basically a decorrelation filter and I have often hypothesized that a reverb unit for only the subs would be an effective means of decorrelating the subs.

Care to postulate on equipment and approaches that could be used to try this out?
post #443 of 665
I'd like to see the recording industry educated (particularly on the music side). Each sound engineer seems to do 'whatever' and attempts to reproduce what they heard (or thought they heard) is a hit or miss effort. On the other hand, a good go at a windmill could prove to be more productive.
post #444 of 665
It looks to me like one could use the Behringer reverb unit. It has two channels. Lets say you have three subs. Now you want them all decorrelated so you feed one with the raw signal and the other two through the reverberator, one each channel. The settings on the two channels need to be different. Remember we are talking here about adding this effect ONLY to the subs not the mains - its a narrow LP bandwidth certianly all below 100 Hz, 150 Hz at best. Set the two reverbs to have a small initial delay with no "early reflections" just late reverb. The reverb tail should damp faily quickly, but trial and error here would be best. This will make all three sub uncorrelated to the extent of the direct to reverb ratio in the reverb unit. All reverb and they are completely decorrelated, some direct signal and they are only partially decorrelated. I'm looking for a reverb unit that also have some EQ as then the subs could be setup and the LFs EQ'd in the same unit. The Behringer lacks any EQ.

Subjectively the added "tail" on the bass signal will help to reinforce the perception of its loudness without it actually being any higher SPL. Its the duration of the bass in a large room that makes it so clear and audible. Small rooms just don't have this as there aren't enough modes to carry the energy. This whole idea came to me when I was at a David Sanborn concert. My brother, a bassist, asked why it was that the bass in a big room is always so "clean" (his subjective term). I've been thinking about this ever since. Coupled with the fact that my PhD thesis was on small room modes and I knew what the issues were there I found that this time of decay thing for LFs is significantly different in small rooms than larger ones - in addition to the obvious modal difference. Then if you look at what it takes to decorrelate LF signals and you find that its basically a reverberator it all comes together and makes sense. You get the same answer coming at it from two different approaches.
post #445 of 665
Quote:
Originally Posted by Dennis Erskine View Post

I'd like to see the recording industry educated (particularly on the music side). Each sound engineer seems to do 'whatever' and attempts to reproduce what they heard (or thought they heard) is a hit or miss effort. On the other hand, a good go at a windmill could prove to be more productive.

22 years ago I applied for jobs as a recording engineer with a Masters degree in Sound Recording. I was told by the people interviewing me that I was over-educated and advised to lie about my tonmeister training if I wanted to get hired (no one even knew what the word Tonmeister meant back then). Nearly every studio I went to had Yamaha NS10's with tissue paper over the tweeters to ostensibly correct a brightness that was due to the rising response in the woofer - not the tweeter (I'd already measured them at NRC).

At that point, I decided to go back to the NRC in Ottawa and work in the sound reproduction side of the business as a scientist where education was considered an asset and strongly encouraged.
post #446 of 665
I understand. I visited a studio using Jensen Triacs mounted in kleenex boxes! During the development of the Soundstream system, we were too educated to know anything about music reproduction.
post #447 of 665
Quote:
Originally Posted by Dennis Erskine View Post

I understand. I visited a studio using Jensen Triacs mounted in kleenex boxes! During the development of the Soundstream system, we were too educated to know anything about music reproduction.

Yes, I could tell by your reference to windmills that you'd had some similar experiences with the music industry like mine Dennis:I didn't know you were involved in Soundstream - the first digital recording company started by Thomas Stockham. I'd like to hear more about that experience.
post #448 of 665
"non-influential" comes to mind; but, it does sound like an excellent excuse to raid someone's wine cabinet.

The story (several of them actually) are fun and interesting. Ingelbretson and I went back several years prior to his involvement, and Stockham and I met when I was in the Physics department where I did ugly things with a PDP11/60. I had a connection with Maestro Abravanel so that's how it all came together.
post #449 of 665
Quote:
Originally Posted by Tonmeister2008 View Post

22 years ago I applied for jobs as a recording engineer with a Masters degree in Sound Recording. I was told by the people interviewing me that I was over-educated and advised to lie about my tonmeister training if I wanted to get hired (no one even knew what the word Tonmeister meant back then). Nearly every studio I went to had Yamaha NS10's with tissue paper over the tweeters to ostensibly correct a brightness that was due to the rising response in the woofer - not the tweeter (I'd already measured them at NRC).

At that point, I decided to go back to the NRC in Ottawa and work in the sound reproduction side of the business as a scientist where education was considered an asset and strongly encouraged.

Which was probably a wise move

You're not the only one to have such experiences. Sad. True.

I've seen more than one or two people dismiss science as "you guys in the ivory towers who have never done any real work". In fact, I think you were in the audience when somebody said that to me at a panel in New York, in regard to loudness measurement.
post #450 of 665
I was a recording engineer (did sound mixing for Earl Klugh) for a short time right after I got my MS. I tired quickly of making excuses for being educated. The advanced degree was a serious impediment to be accepted. Knowing what you are talking about also seemed to be a problem in the recording business. You needed to come up through the ranks, believeing what "they" belived and talking like they talked. Science was not part of the job.

PS. Anybody know why I don't get notification on any posts? Its checked in my profile.
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