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Are audio companies all involved in a huge conspiracy? - Page 20

post #571 of 3048
Quote:
Originally Posted by sdurani View Post

Or you have personal experience that counters some of his conclusions. If you're going to follow Toole's advice and set up a listening room based on your preferences, then you have to be careful not to let others tell you what your own preferences are. As the number of speakers keeps increasing, how audible do you think reflections will continue to be compared to sound coming directly from all those speakers?
I am not talking about MY preferences (or really any others for that matter). I am talking about Toole and studies that may be counter to his. I said something about Earl Geddes at a recent CEDIA seminar and he said, well, yes he has his "opinions". I took that to mean studies of preferences are different than just having one:-) I don't know the answer to the second question but I guess you are makng the point that the speakers would override the reflections. If not, please let me know if that is what you are saying or if you are just asking the question of me. I don't really know the answer and was just throwing it out for discussion. Not sure why I became defensive when I read your reply. I am sure you didn't mean it demeaningly.
Edited by Randy Bessinger - 10/5/12 at 3:09pm
post #572 of 3048
Quote:
Originally Posted by goneten View Post

Okay, but there is no evidence published in any peer reviewed journals, correct?
"Invariably, by the time I get to this point of the argument with someone, the conversation turns into “yes but… is it audible?” As unfair as it might be, I am going to punt that question."
Can you guess who wrote that?
post #573 of 3048
Quote:
Originally Posted by amirm View Post

So no, as a matter of engineering you cannot say it is impossible for the cable to make a difference in audio. It can.
Who argues that? None of the frequent posters in this thread who I am familiar with would say "cables don't make difference". They can depending on their length.
post #574 of 3048
Quote:
Originally Posted by goneten View Post

Okay, but there is no evidence published in any peer reviewed journals, correct?

There was at least one article in the Journal of the AES that showed nobody could hear even very high amounts of jitter. Amir is correct that audio over HDMI can have much higher levels of jitter than normal S/PDIF, but even at those elevated levels it's not likely to be audible. The claim that jitter subtly reduces clarity, or sound stage width, or "fullness" etc are fraudulent, which was your original question.

--Ethan
post #575 of 3048
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There was a paper written by some Japanese guys I think. There is also this Dolby paper. I know Chu has the Dolby paper. I shared the former one here in AVS. Guess who attacked me for committing that sin?
Quote:
There was at least one article in the Journal of the AES that showed nobody could hear even very high amounts of jitter.

There have been AES conference papers, but those are not strictly peer-reviewed. I don't recall ever seeing one that got published in the print journal.
post #576 of 3048
Quote:
Who argues that?
If Amir were limited to arguing about things people actually said, he'd be mute.
post #577 of 3048
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You can then wave your hands on whether it is audible given the fact that there are no listening tests of any kind
Bulls**t. Dunn did listening tests. If you don't like his results, you can do your own. But until you do, we've got evidence, and you don't.
post #578 of 3048
Quote:
Originally Posted by amirm 
I thought you were looking for justification to say that it is impossible for the cable to make a difference. The data I gave you shows that as a matter of engineering, you can't say that.

I don't recall saying anything of the sort. I just wanted to know if there was any concrete evidence that jitter in HDMI cables was audible. From what I understand (since I'm no digital cable guru) is that you either have a reliable HDMI cable or you don't. An unreliable HDMI cable can give you audio drops, pops and blocky, snowy images. A reliable cable is the opposite - no blocky or snowy image, no audio drops or pops.

So we know if the connection is secure and reliable that is a good thing for everyone. Now then, how do we go from unreliable to reliable and then from reliable to "WTF"? OMG, the sound transformed, bass is much deeper, more insight into recordings etc"? Amir, I've been told that you are one of the most knowledgable sources of information on this very topic and so I decided to seek you out.

I for one am glad I did. You talk and I listen.
post #579 of 3048
Quote:
Originally Posted by amirm 
So no, as a matter of engineering you cannot say it is impossible for the cable to make a difference in audio

I don't believe I said that.
post #580 of 3048
Quote:
Originally Posted by amirm 
The graph by the way in my article on cable induced jitter, came from an Audio Engineering Society recommendation for digital audio, "AES information document for digital audio engineering — Guidelines for the use of the AES3 interface": http://tvit.org/GuyCD/Reports/Conference/aes-2id-1996.pdf

It doesn't get more peer reviewed than that smile.gif

There are a couple of graphs. One shows cable induced jitter in a 100 meter (330 foot) digital cable; the other shows cable induced jitter when using an analog cable instead of a digital cable to transmit a digital signal. There is no data in the article or elsewhere which shows that even in those two extreme cases, the cable induced jitter is audible. So while the paper may be peer reviewed and published in the JAES, it doesn't stand for the proposition that cable induced jitter is a problem if you use the right cable in any ordinary length. More intellectual dishonesty from amirm.
Edited by audiophilesavant - 10/7/12 at 10:29am
post #581 of 3048
Quote:
Originally Posted by Amirm 
I thought you were looking for justification to say that it is impossible for the cable to make a difference.

I don't believe I said that either. I'm sure there are some measurable differences between HDMI cables, however minute, so you could say there are differences. What I wanted to know is whether there is evidence to support the assertion that it is audible. Your peers say no. What is your position, Amirm?
post #582 of 3048
Quote:
Originally Posted by hd_newbie View Post

As mentioned by Arny many times HDMI jitter is multiple times lower than what we get through analog. I know this is not question, but I thought it was an interesting piece of knowledge when I first heard.
Hopefully you also realized the really interesting bit there: that psychoacoustics of those two domains paints an entirely different picture with regards to audibility than what one thinks. Higher levels of "jitter" are by no means more audible! The spectrum is the "high order bit" that matters, not the amplitude. You know nothing about jitter audibility without it.

As I explained in my article jitter creates distortion sidebands that are distanced from the music tone by the frequency of jitter. In analog, speed variations are measured in single digit Hertz. In digital, the jitter can be any frequency well into Kilohertz. Why is this significant? Because a psychoacoustic factor called masking. This says that if a signal is in the shadow of another, it may not be heard or heard as much. Masking is strongest when you get very close to the source frequency which would is the case with analog speed variations. As I just explained, in digital jitter frequency can be and is much higher and hence masking may not get triggered at all. In discussing this topic with Arny, I showed him this graph:

i-bSLwHw3-XL.png

"Masker" is our music signal and the blue and red are equal distortions created by same amplitude jitter but at different frequencies. We clearly see that the higher frequency jitter in red is audible since it is outside of the "masking threshold." Notice how I can half its height/amplitude and it would still be audible since it is above the threshold of hearing represented by the bottom u-shaped graph. The blue on other hand, representing much lower frequency jitter (i.e. as in analog) is completely in the masked area and hence probably not audible at all. This is why we say that spectrum of jitter is more important than its amplitude. The nature of the beast needs to be analyzed as we did with room acoustics. BTW, this is at the heart of lossy audio compression like MP3 and how we can compress the signal 12:1 and still have it sound pretty high fidelity. We get to take a lot of the signal because they were not audible at the start.

The reason we still hear WoW and Flutter (i.e. the speed variations in analog above) is due to an entirely different set of reasons having to do with the signal level itself being modulated. It is this modulation that we hear, and not the sideband distortions generated. I showed an exhaustive proof of this relative to its psychoacoustics to Arny who kept arguing otherwise using his own text references in this post, http://www.avsforum.com/t/1340051/seeking-education-about-those-ultra-expensive-interconnects/1830#post_20710842 and follow up to his rebuttal: http://www.avsforum.com/t/1340051/seeking-education-about-those-ultra-expensive-interconnects/1830#post_20713767.

Here is his agreement to the above:
Quote:
Originally Posted by arnyk View Post

Amir, I have already admitted this this was an error in a reply to John Atkinson in post 1768.

In some sense the analog guys are damn lucky. Their systems do have a lot more distortion but they happen to often be of the kind that is far less audible as I have shown here.

So again we need to get past simple talking points here and peel the layers of the onion to understand the true nature of these things.
post #583 of 3048
Quote:
Originally Posted by Randy Bessinger View Post

I don't know the answer to the second question but I guess you are makng the point that the speakers would override the reflections. If not, please let me know if that is what you are saying or if you are just asking the question of me. I don't really know the answer and was just throwing it out for discussion.
Just asking your opinion. My first Lex processor in the mid '90s came with an instruction manual as well as "theory & design" manual that explained the science behind their proprietary surround processing modes. One of the things it mentioned was that the more the room was dampened, the better you could hear their processing create a different (larger) space. I used to take that for granted until a few years ago, when I started looking into whether the conventional wisdom on reflections was all that wise. The graph I posted earlier suggests that early reflections would have to be awfully loud (i.e., louder than the direct sound from the speaker) in order to have a negative impact on the sound. With 2 speakers, the room becomes the surround processor, and so much of what you're hearing is the room. When you have 11 speakers (7.1 + wides + heights), ambience, envelopment, imaging stability, soundstage width & height, etc., are delivered by the speakers. Makes me wonder whether reflections will be able to compete with all that, let alone need deadening.
post #584 of 3048
Wouldn't jitter also be introduced during the recording and mixing process?
post #585 of 3048
Quote:
Wouldn't jitter also be introduced during the recording and mixing process?
Only if you're converting it to analog at some point along the way.
post #586 of 3048
My prediction:
Quote:
Expect a lot of handwaving and diversion from the usual suspect,
The outcome:
Quote:
Originally Posted by amirm View Post

Hopefully you also realized the really interesting bit there: that psychoacoustics of those two domains paints an entirely different picture with regards to audibility than what one thinks. Higher levels of "jitter" are by no means more audible! The spectrum is the "high order bit" that matters, not the amplitude. You know nothing about jitter audibility without it.
As I explained in my article jitter creates distortion sidebands that are distanced from the music tone by the frequency of jitter. In analog, speed variations are measured in single digit Hertz. In digital, the jitter can be any frequency well into Kilohertz. Why is this significant? Because a psychoacoustic factor called masking. This says that if a signal is in the shadow of another, it may not be heard or heard as much. Masking is strongest when you get very close to the source frequency which would is the case with analog speed variations. As I just explained, in digital jitter frequency can be and is much higher and hence masking may not get triggered at all. In discussing this topic with Arny, I showed him this graph:
i-bSLwHw3-XL.png
"Masker" is our music signal and the blue and red are equal distortions created by same amplitude jitter but at different frequencies. We clearly see that the higher frequency jitter in red is audible since it is outside of the "masking threshold." Notice how I can half its height/amplitude and it would still be audible since it is above the threshold of hearing represented by the bottom u-shaped graph. The blue on other hand, representing much lower frequency jitter (i.e. as in analog) is completely in the masked area and hence probably not audible at all. This is why we say that spectrum of jitter is more important than its amplitude. The nature of the beast needs to be analyzed as we did with room acoustics. BTW, this is at the heart of lossy audio compression like MP3 and how we can compress the signal 12:1 and still have it sound pretty high fidelity. We get to take a lot of the signal because they were not audible at the start.
The reason we still hear WoW and Flutter (i.e. the speed variations in analog above) is due to an entirely different set of reasons having to do with the signal level itself being modulated. It is this modulation that we hear, and not the sideband distortions generated. I showed an exhaustive proof of this relative to its psychoacoustics to Arny who kept arguing otherwise using his own text references in this post, http://www.avsforum.com/t/1340051/seeking-education-about-those-ultra-expensive-interconnects/1830#post_20710842 and follow up to his rebuttal: http://www.avsforum.com/t/1340051/seeking-education-about-those-ultra-expensive-interconnects/1830#post_20713767.
Here is his agreement to the above:
In some sense the analog guys are damn lucky. Their systems do have a lot more distortion but they happen to often be of the kind that is far less audible as I have shown here.
So again we need to get past simple talking points here and peel the layers of the onion to understand the true nature of these things.
Looks like I nailed it.
post #587 of 3048
Quote:
Originally Posted by mcnarus View Post

My prediction:
The outcome:
Looks like I nailed it.
But that's so easy to do these days. It's been his marketing pattern for quite some time now.
post #588 of 3048
Quote:
Originally Posted by goneten View Post

I don't believe I said that either. I'm sure there are some measurable differences between HDMI cables, however minute, so you could say there are differences. What I wanted to know is whether there is evidence to support the assertion that it is audible. Your peers say no. What is your position, Amirm?
My position on HDMI is simple: don't use it for critical listening. The combination of HDMI transceivers at both ends and the cable produce unacceptable jitter that can be demonstrated to be well above threshold of hearing. And indeed done so in more than one paper published in AES (e.g. Is the AESEBU / SPDIF Digital Interface is Flawed? paper by Hawksford and Dunn where they show even issues with that interface let alone HDMi with its worse jitter). So personally I would not mess around with the cable to get better sound. The whole interface is suspect at the start. To wit, there is a new technical committee in AES focused on High Resolution Audio. They had this to say in their January 2012 paper titled, Trends in High Resolution Audio:

"HDMI, the point-to-point connector required for BR [sic, Blu-ray] and HD video, has excellent bandwidth and an Ethernet data link (HDMI 1.4), but lacks an audio clock. HDMI receivers must derive audio word clock from the video pixel clock, commonly resulting in very high jitter that affects quality and can be audible. Some high end receivers address the jitter and many companies are researching it but current solutions are expensive and uncommon."

I have never seen any measurements of audio with relation to the HDMI cables alone. So I can't answer your specific question of how much difference it makes. When I have some time to kill, I might try to characterize it. It is very challenging because how a cable works is to some extent dependent on its endpoints. For now, if I am stuck with HDMI, my priority is having it work reliably. I personally don't care about variations causing audio fidelity differences.
post #589 of 3048
Quote:
Originally Posted by sdurani 
When you have 11 speakers (7.1 + wides + heights), ambience, envelopment, imaging stability, soundstage width & height, etc., are delivered by the speakers. Makes me wonder whether reflections will be able to compete with all that, let alone need deadening.
Entirely possible. However, I also wonder if with 11 speakers and good processing you will "need" the room for the increased spaciousness reflections may provide and which research seems to indicate most people prefer.

As I described in a previous post, sidewall reflections shouldn't be difficult to emulate at all with processing and wide speaker placements. I know this is essentially what DSX does. Whether people prefer the real thing over the emulation I think is an interesting question... I'll follow up with a post about that specifically.

What would seem to suffer by having a lively room with lots of speakers is that you may lose flexibility to tailor the room via the dsp processor capabilities. If you wanted, say, a more lively room (sound) with two channel sources, more dead room (sound) with multichannel sources, or different for music vs movies, or even genre's of music, or perhaps even variable as volume level changed, or variable for how many people are in the room... the possibilities are nearly endless, and no doubt at some point in the future we will have a processor capable of exposing this flexibility to savvy users who want it. Perhaps Atmos or similar will help speed that development. But if the room is already quite lively, relatively, you may limit just how much you can vary that processing.

On the other hand, the downside of a relatively dead room is that it isn't a comfortable environment for most people to sit and casually chat. Maybe good for dedicated environment, not so good for multipurpose environment. Of course Lexicon has already experimented with electronic methods of combating that as well...
Edited by Bigus - 10/5/12 at 10:21pm
post #590 of 3048
Ethan,

Since the question of how to perform a proper test was never answered directly, I'll give it a shot. I started thinking about this months ago and started a thread about it... lots of discussions, few good suggestions (IMHO). Having thought about it more, I think perhaps the problem isn't so insurmountable. And in a very practical way, as per my post to sanjay above, perhaps the application goes beyond testing to how we might approach an actual listening space.

Absorbed sidewall reflections vs preserved sidewall reflections... To me, the easiest way to tackle this is to replace a physical reflection with a simulated one, by placing speakers at the first reflection points in a room with very well damped sidewalls. The actual speaker type used might have some effect on the outcome, but I wouldn't expect very much, so long as the wides are identical to the fronts.

Creating the simulated reflection shouldn't be difficult. There are off-the-shelf processors that allow you to add variable delay to a signal. Dabbling in the recording/mixing side of things as you do, perhaps you already have something with that capability. If not, a minDSP could probably handle all of this easily. A copied, slightly attenuated, appropriately delayed version of the respective L or R front channel is a good first approximation. This should be quite easy to test by muting and unmuting the wide channels. I have no doubt that even blinded you will know which is which, so I don't know that this control would remove your existing bias, even if you tried to randomly select on or off wides. i.e., I think in your specific case, there is likely no use for blinded listening. But you could certainly do this for friends and others that may not have recently participated in such a discussion, may not have thought nearly as much about the topic, and indeed may not have the existing biases. Ideally, you may even want to tell them you want help testing something else, like an EQ tweak you have made, or two different surround processing modes being applied to only the front channels (i.e., tell them the wides are off the whole time). The best controls are sometimes when the subjects being tested aren't even aware of what they are being tested for, especially when audibility is established and it is preference we are after.

This testing could be expanded by modifying the wide channel signals. Change the EQ to simulate front speakers of differing off-axis response. Mix in a copy of the contralateral and or center channels which is more attenuated and delayed to move beyond a first order approximation. Do we like reflection of only the ipsilateral side (ala ambiphonics) or like the increased richness (or muddiness) from the crosstalk? How does our preference shift with levels of delay or gain of the reflection? Are preferences the same for "stereo" vs "multichannel" playback? Lots of things could be tested this way more thoroughly than I find in the current literature.

Cost should be rather low. Room treatments to sufficiently damp natural sidewall reflections (I have no space I can currently do this in or I would consider doing it myself). Another pair of identical speakers and amplification. Processor, whether off-the-shelf, PC, or miniDSP. Might be doable in a budget fashion for a grand or so. Perhaps a few grand to ensure quality speakers and adequate treatments. Certainly not a fortune.

The best part, as per the above post to sanjay, is that this reasoning might be extendable to real listening environments as processors improve. And that means more treatments to create the dead environment needed.... equals more business for you! smile.gif Hey, maybe you should champion this approach and hook up with DSX or a studio processor solution to help sell more acoustic treatments. biggrin.gif
Edited by Bigus - 10/5/12 at 10:26pm
post #591 of 3048
Amirm, if the HDMI cable gives audible pops, or drops out completely, shows sparkles etc ... is that related to jitter or completely unrelated? Thank you so much for your involvement here.
post #592 of 3048
Quote:
Originally Posted by goneten View Post

Amirm, if the HDMI cable gives audible pops, or drops out completely, shows sparkles etc ... is that related to jitter or completely unrelated? Thank you so much for your involvement here.
Thanks for the kind words. The answer to your question is "kind of." Take a look at this comparison of a good transmission over HDMI and a bad one:

eye_diagram.jpg

The quality metric is called an "eye" pattern. An "open" eye pattern has pulses that transition from low to high fast enough and without too much side to side movement (jitter) as to allow easy discrimination by the receiver. This is the picture on the left. If a cable for example has high frequency loss which can occur if it is low quality or too long, the transitions take longer which means they straddle the zero crossing longer (more closed eye pattern on the right). This causes more jitter in the receiver meaning there may be times that it can't lock onto the incoming signal correctly and you get those temporary failures (whether that happens is often data dependent).

Note that there are differences just like audio in receivers with respect to how tolerant they are. Some will be better than others in dealing with the upstream degradation. Likewise, some transmitters put out a signal with too much jitter to start and the cable situation then aggravates it. Even on the same receiver, one input may work better than the other as the designer didn't know to keep their lengths to the receiver the same and avoid sharp bends.

An easy way to determine if you have a cable problem is to reduce the resolution. Go from 1080p to 720p or even 480p. If the problem then goes away then you do have a transmission problem. For a constant amount of jitter, the higher the transmission speed, the more damage it causes. If reducing the resolution doesn't makes a difference then likely it is not a cable. Solutions if it is, include using an equalizer that boosts the high frequencies at the start so that even though they are attenuated on the cable, they arrive at the right amount. Alternatively you can use HDMI to cat-5/cat-6 adapters at each end and use that kind of cabling although there are a lot of bad devices of this type which can create their own problems. HDBaseT devices do the best job here.
post #593 of 3048
Quote:
My position on HDMI is simple: don't use it for critical listening.
This position is not supported by the data that has been presented so far, but it's not an unreasonable position.
Quote:
The combination of HDMI transceivers at both ends and the cable produce unacceptable jitter that can be demonstrated to be well above threshold of hearing.
You may believe it can be demonstrated. Unless you've got data you've previously denied the existence of, it has not yet been demonstrated.
Quote:
And indeed done so in more than one paper published in AES (e.g. Is the AESEBU / SPDIF Digital Interface is Flawed? paper by Hawksford and Dunn where they show even issues with that interface let alone HDMi with its worse jitter).
The relevance of concerns about SPDIF to HDMI is highly questionable.
Quote:
"HDMI, the point-to-point connector required for BR [sic, Blu-ray] and HD video, has excellent bandwidth and an Ethernet data link (HDMI 1.4), but lacks an audio clock. HDMI receivers must derive audio word clock from the video pixel clock, commonly resulting in very high jitter that affects quality and can be audible. Some high end receivers address the jitter and many companies are researching it but current solutions are expensive and uncommon."
Not having access to this paper, I don't know the basis for the clause in bold. I'm gonna go out on a limb here and speculate that the technical committee has not actually done listening tests to confirm this. Perhaps they have measurements that show jitter reaching known audible thresholds. If so, I'd like to see them. But this sentence could be read to mean something less than definitive; i.e., that jitter can be high enough to be audible, rather than that the level seen in HDMI are necessarily that high. Without further clarification, I'll have to reserve judgment.

However, the Paul Miller article listed one receiver with an HDMI jitter spec of only 50 ps. This suggests that HDMI is capable of very low jitter, and that the problem may be one of implementation. Note that I said "suggests."
post #594 of 3048
Quote:
Originally Posted by amirm View Post

My position on HDMI is simple: don't use it for critical listening.
What connection do you use for multi-channel SACDs and Blu-ray audio discs?
post #595 of 3048
I thought that with Blu Ray and the hi-rez codecs that there was no jitter because the clocking was done after "unpacking" the codec at the pre-amp. If that's the case, wouldn't the cable be irrelevant?
post #596 of 3048
Quote:
Originally Posted by Ethan Winer View Post

Yes, and I made the same point there that I've made here many times, that nobody seems to consider: Whether side-wall reflections are desirable or not depends in large part on the size of the room.

Well I have certainly considered it, and brought it up several times in the context that there's no "standard' room or MLP in real world applications.
In reality, isn't not treating first reflections just a room treatment "option".
To speak of room treatments in the same context of disingenuous audio marketing or products seems like a huge waste of bandwidth.
post #597 of 3048
Quote:
Originally Posted by Bigus View Post

To me, the easiest way to tackle this is to replace a physical reflection with a simulated one, by placing speakers at the first reflection points in a room with very well damped sidewalls.

I'm sure that would work, but it leaves room for naysayers to dispute whether this is the same as bare walls versus absorption. To be bulletproof, the test really should be with and without absorption.

BTW, I did such a test in 2009 in my living room, but the result wasn't compelling enough. I recorded music in stereo at the listening position with all of my first reflection absorbers in place, then covered every one with a 2x4 sheet of Masonite, and also laid Masonite sheets on the floor at those reflection points. It was a huge PITA to buy and schlep the material, and climb on a ladder to cover the ceiling absorbers. It took an entire day. But the difference as recorded wasn't as obvious as the difference heard in the room. This is a shame, because then people could listen and choose their preference without the hassle of movable panel covers. I'm not wiling to do that again, but if I did I'd rent one of those dummy head thingies, and let people listen on earphones. That's still not the same as absorbers versus no absorbers live in the room through loudspeakers, but it might be a better comparison than what I did.

Speaking of an entire day, I've done lots of tests in my company's "lab" room, and every one was an all-day affair. But to do what Amir expects would be vastly more effort. (Note how easy it is for him to make demands, but how hard it is to answer my question about what test he'd consider valid.) Maybe we don't really need motor driven panel covers. Maybe just covers on clips that could be attached in five minutes. But as far as I'm concerned this is moot and unnecessary, because everyone I know greatly prefers absorbers. biggrin.gif

--Ethan
post #598 of 3048
Quote:
Originally Posted by rnrgagne View Post

To speak of room treatments in the same context of disingenuous audio marketing or products seems like a huge waste of bandwidth.

Yet this is exactly what Amir does anyway. rolleyes.gif

I'm still waiting for Amir to show me the blind preference tests to back up half a dozen claims on his own company's web site I listed. Did anyone else notice that he ducked that completely?

--Ethan
post #599 of 3048
Quote:
Originally Posted by Bigus View Post

I also wonder if with 11 speakers and good processing you will "need" the room for the increased spaciousness reflections may provide and which research seems to indicate most people prefer.
Early reflections can do more than encourage spaciousness, they also help with articulation and making colourations/resonances less audible. In my experience, reflections also act like a glue between various channels, helping to blend speakers into a seamless ring of sound. Sort of a connecting-the-dots effect vs sounding more like 5 or 7 pools of mono placed around the listener.
Quote:
Originally Posted by Bigus View Post

As I described in a previous post, sidewall reflections shouldn't be difficult to emulate at all with processing and wide speaker placements.
That's kinda what Haas did in his early experiments. Not having access to an anechoic chamber, he used the roof of a building (no walls), placing a "source" speaker about 10 feet in front of the listener (not too different from a typical home set-up), with a speaker at ±45° to either side to simulate a single early reflection. The test subjects adjusted a volume knob until they felt the reflection was as loud as the source, leaving Haas free to experiment with a single variable: delay.

During the first 5-30ms, listeners only heard the sound as coming from the source speaker (first arrival of the sound) and not the reflections (delayed copies of the same sound). And this is under the worst conditions, where the reflection was as loud as the source (imagine your room walls being made of material that had 0% absorbtion and was 100% reflective). In fact, in that delay range, Haas could ramp up the reflection speaker up to 10dB louder than the source speaker without it being heard as separate. That's loud, and not something you're likely to experience with reflections at home.

So what you're describing not only works, but has been used for over 60 years to test the effect of reflections in a precise and controlled manner.
post #600 of 3048
Quote:
Originally Posted by Ethan Winer 

I'm sure that would work, but it leaves room for naysayers to dispute whether this is the same as bare walls versus absorption. To be bulletproof, the test really should be with and without absorption.

No doubt, but I still think this would be hugely beneficial research. Comparing the simulation to real to see which is then preferred would also be necessary at some point (and quite useful for the dsx and similar researchers) but obviously the more difficult undertaking.

The great advantage of testing using the simulations is that the switching can be instantaneous and easily randomized, and you also don't need real blindfolds. wink.gif

But.the biggest advantage for you is that if you convince people this is the way to get the best sound, either with or without reflections, they need lots of your absorbers either way. biggrin.gif
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