Envelopment: Toole, Multichannel, Binaural

[Scott Borduin]

As mentioned on a previous thread, I have been doing a lot of research and thinking about the basic paradigms of audio as they relate to the goal of more realistic, natural reproduction - of music, in particular. A lot of this thinking was inspired by reading the latest version of Floyd Toole's book: https://tinyurl.com/y8am5le7 , which is pretty much mandatory reading for any science-oriented audiophile, IMO. Further insights came from this book: https://tinyurl.com/y8gg8kyz , which is a publication of the AES and therefore more technical, but still enlightening even for the non-mathematically inclined. I apologize if a lot of this post is too pedantic, familiar, or obvious, but to have a productive discussion on this it seems important to be on the same page to start.

To start with, here are some basic observations from Toole that I am treating as core assumptions. I suspect that these core assumptions will not be uncontroversial but they are backed by a lot of hard and empirical science at this point.
1. The basic signal path from microphone through recording, storage, and playback all the way to the loudspeaker is now sufficiently perfected that it has minimal to no impact on the quality of reproduction.
2. Loudspeaker design, as it relates to perceptual quality, is now a quite well-understood discipline. Speakers exhibiting flat on-axis response and even directivity will be highly rated for naturalness by a broad cross section of listeners across a broad range of physical conditions and program material.

In other words, we've now reached a high plateau of performance in all the basic elements of sound recording and reproduction, from mics to digital recording to electronics to speakers. And yet: nobody who goes to concerts on a frequent basis is ever fooled into believing that their stereo system recreates the experience of a musical event in a concert hall or other performance space. The two books I reference above describe the problem in gory detail, but you can boil it down to one word: stereo.

On the face of it, stereo is an attractively simple concept for recording and reproducing music. We have two ears, stereo has two channels. Record those two channels accurately, deliver them to your ears, viola. In practice, this simplicity is undone by a number of problems, but the two most glaring defects are both related to the same issue: we hear each channel with both ears.

Stereo defect number 1 is the most obvious and familiar - stereo does not recreate the full sense of space, immersion, envelopment we hear in an actual performance space. Why is this? To start with, our sense of being in a performance space comes from reflected sounds, sounds that bounce off the walls and ceiling of the space (the floor level is usually covered by absorbent people). As it turns out, the most important of these reflections from the perspective of envelopment are reflections that are "decorrelated" - dissimilar between the two ears. Those reflections will largely be lateral (side) reflections. So to recreate a sense of envelopment, we should start by capturing and recreating these low-correlation sounds at the ears. You see the problem: in conventional stereo, both ears hear both speakers, and the necessary decorrelation is greatly reduced. Recording engineers can do things to partly compensate for this, through microphone arrangements or signal processing that increase the amount of decorrelated sound, but the ear/brain combination is never wholly convinced.

Stereo defect number 2 relates to imaging and timbral accuracy. Think about the center image of a vocalist in a pop recording. The center image is created by routing the same signal to each speaker. Once again, though, each ear hears each speaker. And with speakers placed to the right and left of the listener, the signal will arrive at one ear slightly before the other. The result of combining a signal with a delayed version of itself is a frequency response artifact called comb filtering. In the case of the center image example above, the comb filter will create a strong frequency response dip around 2khz, and some other artifacts as well - see section 7.1.1 of the Toole book. If you have experienced the difference between a system with a physical center channel and a "phantom" center using just right and left speakers, the difference is obvious and "phantom" is not a bad description. And of course, the phantom imaging of stereo loses fidelity when the listener moves or rotates their head.

The two most promising paradigms for fixing/replacing the stereo problem are multichannel and binaural. Given how long this post is already, I'll break each of those into separate subsequent posts.

Scott

 

[Scott Borduin]

So one obvious tack to take when two channels are not enough: add more channels! And indeed, it would seem that more channels can help solve both of the fundamental issues with stereo. But thinking of multichannel as simply "surround sound" misses the fact that Mch solves two different problems in two different ways.

First, the addition of a well-matched center channel for reproducing sounds toward the center of the stage can help overcome the comb filtering problem mentioned above - the center image is now reproduced by a dedicated center speaker, the sound of which will arrive at both ears simultaneously. And of course, the location of the center image will remain fixed in position even as the listener moves. Although it is obviously desirable if a recording is engineered with an explicit center channel, it can also be synthesized to good effect. I personally used Meridian processors for many years, which implement a proprietary version of an algorithm called "Trifield" which upmixes from 2 channel to 3 or more channels. I found that the Trifield mode did a great deal to solidify the center image, and I pretty much always preferred it to straight stereo if the center channel was well matched in response and height (the "ventriloquism effect" works fine when you have a visual image, not so much without). Meridian's Trifield also synthesized side and rear surrounds, which I did not find as convincing. Note that the basic Trifield algorithm is based on simple mid/side extraction, equalization, and matrix mixing of the MS signals - something which might be accomplished using pro audio software plugins, or some of the more advanced consumer software like JRiver and Roon.

Second, the addition of side channels provides a direct way of reproducing decorrelated sounds - reflections - at the listeners ears. Side and rear channels also obviously present the opportunity for artistic possibilities like "middle of the band" perspective, but I'm talking here about the usual perspective of performer(s) up front, listener in the performance space. Reading Toole and listening to his lectures, I had an "aha" moment. It seems that research from multiple sources on concert hall design suggests that the sense of envelopment is maximized by reflections from a frontal angle of about +-60 degrees (apparently the classic highly regarded "shoebox" hall design tends to create reflections from these angles). So if we want to create maximum envelopment, why aren't our side speakers located at +-60 degrees instead of the usually specified 90-110 degrees? The answer, of course, is that multichannel specifications are designed to recreate movie sound effects, not necessarily concert hall envelopment.

For a time, I experimented with true discrete multichannel, but was never fully satisfied with the results. To my ears, the surround channels tended to pull the stereo image forward, and add some spaciousness, but real envelopment seemed elusive. Perhaps it was just my particular setup, or I just never found the right recordings, but I wonder what would have happened had I just known to experiment with surround channels placed further forward. Toole himself suggests a "9.1" configuration with the two extra speakers at +-60, decorrelated from the side channels via simple delay of 10 ms or so (in a post on AVSforum, the link to which I have lost).

In any case, I gave up on Mch a few years back, partly because I wasn't getting the results hoped for, partly because multichannel didn't lend itself well to ripping and playback in the computer-based audio systems which have become my sole source. But now there are feasible, if not exactly friendly, methods for ripping SACD, and playback software which handles multichannel PCM and DSD. I have some new insights into Mch. There has been progress in extending the Mch paradigm into more channels, especially height channels. The library of multichannel classical recordings continues to grow, despite the seemingly moribund commercial status of the SACD format. And there are new developments in synthesizing surround from legacy 2 channel material. So, having passed the point of diminishing returns in stereo, I intend to jump back into the Mch world and see where it takes me, with more of a determination to maximize the potential this time around.

 

[Scott Borduin]

So, on to Binaural, the other very promising candidate for stereo replacement. Binaural goes back to that simple equation, 2 ears == 2 channels, but tries to fix the fundamental problem of each ear hearing both channels. This turns out to be way more complicated than it sounds

If it was just as simple as eliminating interaural crosstalk - making sure each ear only hears the channel intended for it - we would just put on a pair of headphones with any acoustic stereo recording and viola, we'd be magically enveloped by the sound of the original space. Instead, what happens is we get an orchestra or band playing in inside our head - what is referred to in chapter 4 of the Immersive Sound book as Inside-the-Head Locatedness (IHL) or, alternatively, lateralization. Our ear/brain mechanism stubbornly refuses to recognize the spatial cues embedded in the recording.

It turns out that there are a number of interrelated factors which are suspected in IHL, but two major issues are the Head Related Transfer Function (HRTF) and Motion Invariance. HRTF refers to the phase and frequency response alterations imposed by our torso, head, pinnae (external ears) and ear canals. The sound that reaches our eardrums is highly altered from the external sound, and that alteration is highly dependent on direction. In other words, our ability to sense location of sounds is partly dependent on getting the "correct" frequency and phase response shaping (HRTF) entering our ears - and what is "correct" is different for every person! Conventional stereo mic technique doesn't account for HRTF. Binaural recording with a dummy head does try to correct for HRTF, but by using a generic head/ear shape that might or might not match closely your personal HRTF. No wonder binaural recordings generate such different subjective results.

On top of that, part of the way our ear/brain localizes sound is by detecting the differences in sound as we move our heads - even when those motions are quite subtle. This localization cue is particularly important for disambiguating front from rear sounds. But using conventional headphones, the sound does not change when you move your head. In my personal experience, listening to binaural recordings from Chesky and the like over headphones, I get a strong impression of sounds originating far distant to the sides, but with no sense of depth. The result is more distracting than pleasing for me. I suspect this very much related to the motion invariance problem in my case.

So to create a convincing binaural impression, we must have: 1.) suitable recordings, 2.) a reasonably close match to our personal HRTF, and 3.) motion tracking. Fortunately, the convergence of binaural recording, digital audio processing, and advanced image processing or other motion detection techniques makes it possible to satisfy these requirements, at least in theory. Chapter 4 of the Immersive Audio book lays all of this out.

Even more intriguing to me was chapter 5 of that book, written by Edgar Choueiri, the inventor of the BACCH 3D suite of processing algorithms. BACCH 3D attempts to create binaural audio over stereo loudspeakers, using advanced DSP processing to dramatically reduce interaural crosstalk. And referring back to my post above, interaural crosstalk is the root of stereo's evils. There have been attempts to do this before - I owned a Carver Sonic Hologram back in the day, which created fascinating if not always realistic effects - but it there are some basic mathematical problems which have limited the effectiveness and application of these attempts. While I'm really not qualified to pass definitive judgement, it seems Choueiri has solved the toughest of these problems with BACCH 3D. His system also uses personalized HRTF (via measurements with in-ear microphones) and motion tracking via image processing from a web cam.

Unfortunately, the commercially available BACCH 3D systems range in price from "nice Hawaii vacation" (a Mac software-based solution called BACCH4Mac) to "new car" (all-in-one custom hardware solutions). Nonetheless, I'm intrigued enough to try it sometime soon. In correspondence with BACCH, they claim good results with both ordinary stereo and binaural recordings, and the pro version will also create a binaural representation of multi-channel recordings - for headphones or speakers. And of course cancelling interaural crosstalk also fixes the comb filter problem with phantom center images. We shall see.

Anyway, I see I used up way more pixels than I intended on these topics, but writing it all out was useful for me at least Hopefully, it will stimulate some good discussion as well.

Scott

 

[Cosmik]

I feel sorry for people who don't find that stereo delivers a fair impression of 'live'. I am guessing they may not be starting out with a neutral system that is as free as possible of phase shifts and timing errors. (In the intro, no mention is made of phase and timing; only flat response and even dispersion).

I know that there are people who share my 'ability' to be transported to the venue with stereo, but only with a neutral system. Here is one:

The imaging on these speakers is also absolutely unbelievable, in all dimensions. The front to back depth is unreal; room information is conveyed incredibly well. You’re there. In fact it might be the depth that astounded me more than anything else. The stereo image is absolutely enormous, involving, and everything sounds real.

When I go to classical concerts, I do consciously try to take in whether it sounds vastly different/better than recordings played over a stereo system, and I often conclude that it doesn't. I sometimes put a recording of the same piece on when I get home just to check!

Of course, if you start with a certain idea in mind ('Stereo can't possibly reproduce a satisfying experience' or, in my case, 'I love stereo') what you experience will probably confirm it!

 

[oivavoi]

Wow! Great write-up! The link to that AES book seems broken though?

I agree with most of your points. EDIT: even though I have heard stereo setups which felt real to me, but only when seated exactly in the sweetspot.

I would add that well-designed and well-placed omni speakers also are able to recreate some of that which is often lost with conventional stereo.

Listening to a well-implemented and music oriented m.ch. setup is very high on my todo list this year.

 

[svart-hvitt]

I feel sorry for people who don't find that stereo delivers a fair impression of 'live'. I am guessing they may not be starting out with a neutral system that is as free as possible of phase shifts and timing errors. (In the intro, no mention is made of phase and timing; only flat response and even dispersion).

I know that there are people who share my 'ability' to be transported to the venue with stereo, but only with a neutral system. Here is one:


When I go to classical concerts, I do consciously try to take in whether it sounds vastly different/better than recordings played over a stereo system, and I often conclude that it doesn't. I sometimes put a recording of the same piece on when I get home just to check!

Of course, if you start with a certain idea in mind ('Stereo can't possibly reproduce a satisfying experience' or, in my case, 'I love stereo') what you experience will probably confirm it!

I feel sorry for people who don't find that stereo delivers a fair impression of 'live'. I am guessing they may not be starting out with a neutral system that is as free as possible of phase shifts and timing errors. (In the intro, no mention is made of phase and timing; only flat response and even dispersion).

I know that there are people who share my 'ability' to be transported to the venue with stereo, but only with a neutral system. Here is one:


When I go to classical concerts, I do consciously try to take in whether it sounds vastly different/better than recordings played over a stereo system, and I often conclude that it doesn't. I sometimes put a recording of the same piece on when I get home just to check!

Of course, if you start with a certain idea in mind ('Stereo can't possibly reproduce a satisfying experience' or, in my case, 'I love stereo') what you experience will probably confirm it!

@Cosmik , you wrote:

«I feel sorry for people who don't find that stereo delivers a fair impression of 'live’».

Cinemas left stereo for multichannel ages ago. There is no going back because stereo can’t deliver the multichannel experience. My own estimation is that film audio has made big leaps in the past 5-15 years.

Why should it be otherwise in music (reproduction).

This is not to say that multichannel is easy or cheap. However, the roll-out of high-quality multichannel systems in cinemas indicates that multichannel sound is a complicated problem, not a complex one.

So multichannel is - in my view - undoubtedly superior to stereo. Modern cinemas (of the past 1-5 years) are the evidence in my eyes.

PS: Which is not to say that stereo is «bad». It’s just that stereo can be improved upon.

 

[Phelonious Ponk]

So one obvious tack to take when two channels are not enough: add more channels! And indeed, it would seem that more channels can help solve both of the fundamental issues with stereo. But thinking of multichannel as simply "surround sound" misses the fact that Mch solves two different problems in two different ways.

First, the addition of a well-matched center channel for reproducing sounds toward the center of the stage can help overcome the comb filtering problem mentioned above - the center image is now reproduced by a dedicated center speaker, the sound of which will arrive at both ears simultaneously. And of course, the location of the center image will remain fixed in position even as the listener moves. Although it is obviously desirable if a recording is engineered with an explicit center channel, it can also be synthesized to good effect. I personally used Meridian processors for many years, which implement a proprietary version of an algorithm called "Trifield" which upmixes from 2 channel to 3 or more channels. I found that the Trifield mode did a great deal to solidify the center image, and I pretty much always preferred it to straight stereo if the center channel was well matched in response and height (the "ventriloquism effect" works fine when you have a visual image, not so much without). Meridian's Trifield also synthesized side and rear surrounds, which I did not find as convincing. Note that the basic Trifield algorithm is based on simple mid/side extraction, equalization, and matrix mixing of the MS signals - something which might be accomplished using pro audio software plugins, or some of the more advanced consumer software like JRiver and Roon.

Second, the addition of side channels provides a direct way of reproducing decorrelated sounds - reflections - at the listeners ears. Side and rear channels also obviously present the opportunity for artistic possibilities like "middle of the band" perspective, but I'm talking here about the usual perspective of performer(s) up front, listener in the performance space. Reading Toole and listening to his lectures, I had an "aha" moment. It seems that research from multiple sources on concert hall design suggests that the sense of envelopment is maximized by reflections from a frontal angle of about +-60 degrees (apparently the classic highly regarded "shoebox" hall design tends to create reflections from these angles). So if we want to create maximum envelopment, why aren't our side speakers located at +-60 degrees instead of the usually specified 90-110 degrees? The answer, of course, is that multichannel specifications are designed to recreate movie sound effects, not necessarily concert hall envelopment.

For a time, I experimented with true discrete multichannel, but was never fully satisfied with the results. To my ears, the surround channels tended to pull the stereo image forward, and add some spaciousness, but real envelopment seemed elusive. Perhaps it was just my particular setup, or I just never found the right recordings, but I wonder what would have happened had I just known to experiment with surround channels placed further forward. Toole himself suggests a "9.1" configuration with the two extra speakers at +-60, decorrelated from the side channels via simple delay of 10 ms or so (in a post on AVSforum, the link to which I have lost).

In any case, I gave up on Mch a few years back, partly because I wasn't getting the results hoped for, partly because multichannel didn't lend itself well to ripping and playback in the computer-based audio systems which have become my sole source. But now there are feasible, if not exactly friendly, methods for ripping SACD, and playback software which handles multichannel PCM and DSD. I have some new insights into Mch. There has been progress in extending the Mch paradigm into more channels, especially height channels. The library of multichannel classical recordings continues to grow, despite the seemingly moribund commercial status of the SACD format. And there are new developments in synthesizing surround from legacy 2 channel material. So, having passed the point of diminishing returns in stereo, I intend to jump back into the Mch world and see where it takes me, with more of a determination to maximize the potential this time around.

Seems to me that this...

“The answer, of course, is that multichannel specifications are designed to recreate movie sound effects,”

This, not technical limitations, is the real roadblock. If the ultimate goal is to create concert hall sound, the most fundamental problem is that so few recordings even attempt to capture it in the first place. There are some audiophile and classical recordings that do, using the current multi channel systems, but multi channel is a small fraction of a shrinking home audio market, music, as opposed to movies, is a small fraction of the multichannel content market, and content that aims to reproduce natural hall ambiance (as opposed to, say, five Eagles singing harmony from five different speakers) is a small fraction of the multichannel music market.

There is just not enough money in it to change the way hardware is made, much less recordings. It will have to be synthesized from stereo, or your listening options will be so limited that...well, who was it that said audiophiles use music to listen to their equipment, not vice versa? This is that. In the extreme.

 

[Phelonious Ponk]

I would add that well-designed and well-placed omni speakers also are able to recreate some of that which is often lost with conventional stereo.

Yeah, it might make more sense to pull all the room treatments, use omnis and listen to your room instead of trying to hear another one. The Linkwitz approach. Great observations and ideas here, but virtually no content to test or use it, , and virtually none forthcoming.

 

[Kal Rubinson]

2L has lots of interesting material in 5.1/7.1/ATMOS/Auro-3D. Their demos at AES last November were impressive.

 

[Scott Borduin]

Wow! Great write-up! The link to that AES book seems broken though?

I agree with most of your points. EDIT: even though I have heard stereo setups which felt real to me, but only when seated exactly in the sweetspot.

I would add that well-designed and well-placed omni speakers also are able to recreate some of that which is often lost with conventional stereo.

Listening to a well-implemented and music oriented m.ch. setup is very high on my todo list this year.

Hmm, link works for me. Anyway, the full title of the book is "Immersive Sound: The Art and Science of Binaural and Multi-Channel Audio", if you want to do a search on it. Expensive book, although the Kindle edition is half the price.

I had MBL speakers at one time. I found them to be addicting at first, not so much later on. The problem was that the sense of space was too similar recording to recording - a factor of speaker/room interaction, probably.

 

[svart-hvitt]

2L has lots of interesting material in 5.1/7.1/ATMOS/Auro-3D. Their demos at AES last November were impressive.

@Kal Rubinson , what was the gear 2L used to demo their recordings?

 

[Scott Borduin]

I feel sorry for people who don't find that stereo delivers a fair impression of 'live'. I am guessing they may not be starting out with a neutral system that is as free as possible of phase shifts and timing errors. (In the intro, no mention is made of phase and timing; only flat response and even dispersion).

I know that there are people who share my 'ability' to be transported to the venue with stereo, but only with a neutral system. Here is one:


When I go to classical concerts, I do consciously try to take in whether it sounds vastly different/better than recordings played over a stereo system, and I often conclude that it doesn't. I sometimes put a recording of the same piece on when I get home just to check!

Of course, if you start with a certain idea in mind ('Stereo can't possibly reproduce a satisfying experience' or, in my case, 'I love stereo') what you experience will probably confirm it!

My current stereo system is based on Sanders 10e electrostatics. I go back and forth between manual EQ below 500hz, and full correction with Acourate. These speakers are certainly neutral in the sense of measured and subjective frequency response, and have very good impulse and step response even without Acourate phase correction. I didn't mention phase response above because 1. most of the empirical science does not show it to be a major factor, if even audible with much program material and 2. my own experience with Acourate on several speakers shows subtle effects at best between min-phase and phase correction filters. Certainly nothing that overcomes the basic experience gap between live and reproduced. I've chased the stereo thing for long enough to realize that I'm trying to compensate for limitations that will never be entirely overcome.

I hear things at concerts I've never heard from any stereo system. Solo woodwinds have a sense of size, body, richness live that doesn't come across reproduced. Massed strings, the same. Orchestral climaxes are powerful, engulfing events that can't be duplicated at home by just turning up the volume. All of these things are interactions between ensemble and performance space that just don't come across for me in a convincing way over any of the audio systems I've personally spent a lot of time with. Perhaps I'm too picky about this, and should learn to enjoy just how good I have it! Or perhaps my obsession will lead to a step function change in realism for me. We'll see.

 

[Kal Rubinson]

@Kal Rubinson , what was the gear 2L used to demo their recordings?

I cannot recall. The rack was filled with familiar equipment and the speakers were arrayed all around on a 3D grid. http://www.aes.org/events/143/presenters/?ID=6321

 

[RayDunzl]

stereo can’t deliver the multichannel experience

multi-
ˈməltē/
combining form

1. more than one; many, especially variegated.

Stereo, 2 channels, is, by definition, multichannel.

(sorry)

 

[Scott Borduin]

I cannot recall. The rack was filled with familiar equipment and the speakers were arrayed all around on a 3D grid. http://www.aes.org/events/143/presenters/?ID=6321

Was the demo Auro or Atmos?

 

[tomelex]

My current stereo system is based on Sanders 10e electrostatics. I go back and forth between manual EQ below 500hz, and full correction with Acourate. These speakers are certainly neutral in the sense of measured and subjective frequency response, and have very good impulse and step response even without Acourate phase correction. I didn't mention phase response above because 1. most of the empirical science does not show it to be a major factor, if even audible with much program material and 2. my own experience with Acourate on several speakers shows subtle effects at best between min-phase and phase correction filters. Certainly nothing that overcomes the basic experience gap between live and reproduced. I've chased the stereo thing for long enough to realize that I'm trying to compensate for limitations that will never be entirely overcome.

I hear things at concerts I've never heard from any stereo system. Solo woodwinds have a sense of size, body, richness live that doesn't come across reproduced. Massed strings, the same. Orchestral climaxes are powerful, engulfing events that can't be duplicated at home by just turning up the volume. All of these things are interactions between ensemble and performance space that just don't come across for me in a convincing way over any of the audio systems I've personally spent a lot of time with. Perhaps I'm too picky about this, and should learn to enjoy just how good I have it! Or perhaps my obsession will lead to a step function change in realism for me. We'll see.

I certainly admire your search for a "better sound" for you. But, two channel stereo as you say, well, it was for the movies screen. I too had some issues listening to stereo, changing from mono to stereo on the fly or over extended periods of time, you can hear just how artificial stereo is. It sounds as weird as it is, two point sources trying to create a sense of width (depth while possible is not its strong point nor height) can not fool these ears in the least. I have been an advocate for binaural, despite its limitations, always sounds better to me.

Alas, a long time ago I accepted stereo for what it is, and a lot of learning and experimenting finally allowed me to believe the conclusions logic and my ears provided and so I have no problem accepting it for the "effect" it is. I found that listening for detail provided me with a more enjoyable experience than trying to deal with weird stereo effects and two single point sources. I enjoy stereo for what it is, not what is isn't. However, you need to reach your own conclusions and travel your own path and hopefully finally just enjoy it for what it can do, and not what it can not do-that is a long list indeed!

I would say that although in essence I agree with the comments you quoted in the first post about a fairly well perfected signal chain, it is perfected pretty much in that it takes wiggles in one small area (the mike area) and makes corresponding wiggles out of the speakers, pretty good. If we just wanted to capture one small area of space in time, the chain can do that well. Like you are seeing, though, stereo is not capable of recreating probably more than a few percent of the actual performance vs what you ears hear. So, given it can replicate a few percent of the entire performance (little bits of sound right at the little itty bitty mics) it is actually pretty damn good when you think of it that way. So for me, the more detail I hear, the better the recording and the better the resolution of the system, AS a replicator of the itty bit it can do, however, many audiophiles, including me sometimes, want embellishments to the sound, such as SET to provide more flesh on those skinny little bones of stereo.

It is really a lost cause as a replication system, so it needs help from our imaginations (stereo is only a process we create in our ear/brains) and some have really much better imaginations than others do. Me, not so much imagination, however, knowing and accepting stereo for what it is, and its pretty much all most of us have (guys with multi-channel are way ahead of the rest of us) then I can accept it and since I do not hope for something that it cant do, can simply enjoy it.

Your first few posts were very good at narrowing down some stereo basics, thanks.

 

[Kal Rubinson]

Was the demo Auro or Atmos?

Dunno. I suspect it was Auro. I will ask.

 

[Fitzcaraldo215]

Absolutely awesome, Scott. Beautiful, insightful writing about one of my favorite subjects.

Just a few, ok, more than just a few, comments on part 2 in terms of my own experience:

I do think that the important proof of concept for Mch in music comes down to subjective listener opinions of recorded vs. the recalled sense of live in a dimensional concert space. That seems most meaningful for classical music in good acoustic spaces, which are many, as opposed to rock concerts in sporting areas with PA systems or jazz in acoustically challenged basement clubs with glasses clinking. But, some club and theater venues might offer the possibility of very good Mch recordings for non-classical genres. I just wish that there were more such recordings.

I also don't see much point to Mch for studio recordings, since studios are deadened spaces to facilitate multitrack stereo recordings, including techniques like extensive panning and mixdown. The audible sense of local space captured around a performer's mike does not pan or mix well when combined with other tracks containing the different local space around other performers. Hence, the studio deadens and suppresses them all. Besides, we have no listening experience in the studio. Audiences are not permitted. How would we know?

To be clear, this is not a put-down of most popular recordings, which are an engineered, often brilliant, art form unto themselves. It is just my meager attempt to explain what I think actually happens quite often.

So, in case anyone was wondering why Mch seems to appeal more to classical lovers, especially those who go to live concerts, the above paragraphs may explain why. Also, it might partly explain why Mch lacks as much appeal for rock, jazz, etc., unfortunately.

I really do not like the terms "envelopment" and "surround sound". I think they are easy to misconstrue. Also, the multidimensional space, ambiance, etc. feels totally natural to me live, not specifically "enveloping" or "surrounding", though they are that. The sense of space, ambiance, etc. are just an inseparable part of the total, singular impression of live sound, somewhat vaguely and diffusely. My sense is that good Mch recordings convey this in a similarly natural way, without undue emphasis of the presence of additional speaker channels. That should be totally seamless in a properly set up Mch system. And, I have countless recorded examples of where it is just that.

What I actually feel is that stereo "unenvelops" or "unsurrounds" the listener by truncating those natural, live aural cues on playback. But, you might not notice that too much until the Mch is taken away. We have become acoustomed to stereo sound. I have fooled many a stereo listener on hearing my system. I play in surround, lying to them about the extra speakers being off, then switching to stereo on the same recording. They did not perceive the lie, at first. The sound field, of course, then collapses in stereo. Good music still comes through. But, it does so just over there, up front, no longer providing a room filling "we are there" image. They were, of course, impressed. Some are now devoted Mch listeners, like me.

But, the real point is that the value of Mch audio is often more revealed by its absence rather than by its presence. Sure, the Berlioz Requiem with surrounding brass choirs is spectacular in Mch, way beyond anything stereo can do. But, so are innumerable, non-exotic, orchestra, performers or soloists "up front" recordings by adding back the surrounding space dimension that stereo cannot.

For whoever reasons, I am not a fan of artificial synthesis of additional spatial channels. I believe that the ITU standard for the 5.0/.1 Mch scheme adopted by Sony/Philips for their Scarlet Book for SACD (the SACD equivalent of CD's stereo-only Red Book) clarified and became an important standard for Mch music. That was even beyond SACD, not only in home speaker setup, but also in determining what music recording engineers actually used and aspired to in miking, mixing and production for music playback with most realistic reproduction. At least one Mch label, Channel Classics, uses only a 5 channel ITU mike array. Others may use more mikes, but the same ITU array is the backbone of the setup, and final mixing and mastering is done via an ITU speaker array.

So, I am not enthusiastic about needing to add extra speaker channels at +- 60 degrees in order to possibly create additional "envelopment" beyond what is already there, as captured by mike arrays and engineering according to ITU standards. A pleasurable sonic effect? Yes, possibly. But, is it more "real"? Questionable. I prefer to stay with what the engineers mixed and mastered from mikes in the hall. I have been satisfied with that.

The ITU standard, incidentally, was not developed solely for cinema. Sony/Philips adopted it for the music medium of SACD, greatly improving on prior mistakes, like the Quad 4.0 setup or numerous other misguided experiments. Fortunately, ITU was also quite compatible with developments in HT that materialized and firmed up only later. My ITU speaker array plays brilliantly with both music and with cinema, in my opinion. So, unless a new, widely accepted standard for more discretely recorded channels, such as +- 60, comes along, I am quite happy with where I am.

 

[Fitzcaraldo215]

I feel sorry for people who don't find that stereo delivers a fair impression of 'live'. I am guessing they may not be starting out with a neutral system that is as free as possible of phase shifts and timing errors. (In the intro, no mention is made of phase and timing; only flat response and even dispersion).

I know that there are people who share my 'ability' to be transported to the venue with stereo, but only with a neutral system. Here is one:


When I go to classical concerts, I do consciously try to take in whether it sounds vastly different/better than recordings played over a stereo system, and I often conclude that it doesn't. I sometimes put a recording of the same piece on when I get home just to check!

Of course, if you start with a certain idea in mind ('Stereo can't possibly reproduce a satisfying experience' or, in my case, 'I love stereo') what you experience will probably confirm it!

Yes, old buddy, old curmudgeon, stereo delivers a "fair impression" of live, as did mono for many decades before that. The music comes through in all cases, and it can be enjoyed for what it is. I listen to stereo most of any day on my (cheap) FM radio, and I enjoy the music immensely.

I reach an entirely different conclusion than you, however, on whether a live concert differs "vastly" from even a top quality home stereo. For me, it never came remotely close enough, quite clearly, in spite of some really good audio systems, my own and countless others I heard. I always believed a better replica would be preferable and it might someday be possible. It is still not perfect, but I believe Mch today is a very substantial advance in the right direction. Improving audio systems, reducing distortion, etc. etc. by better science and engineering just does not take us there. Like Scott and Toole, I agree it is the stereo paradigm is seriously flawed if a plausible replica of live is the goal.

YMMV.

 

[Wombat]

Movie application is very different to music reproduction. Movies use effects to simulate off-screen 'occurrences'.

Surround sound for domestic music entertainment is trying to recreate the recorded ambience by modifying the domestic ambience. Music performances generally don't have direct sounds coming from the sides or rear. How are different size/shape listening spaces and speakers accommodated by the recording?
Is it really so good or is it just another illusion/preference?