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Can You Trust Your Ears? By Tom Nousaine

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fas42

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"annoying" is not the only question asked in BS1116. But it does require ABC/hr, and it does require instant switching that does not create artifacts. These properties are an absolute necessity for even moderately sensitive auditory testing.

I'm not sure what you think you were doing, or what kind of sensitivity you believe you need, but what you were doing doesn't seem to be either ABC/hr or BS1116, or Mushra, either.
It's not following any standard method of testing, but I was intrigued that BS1116 focuses on the concept of impairment, and the degree of annoyance registered by the subjects when they become aware of it. This is how I subjectively assess playback, and decide whether changes made are a genuine improvement, or not.
 

j_j

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My hypothesis is that a sufficiently high enough quality of playback allows this behaviour, and I have already stated that it's extremely difficult, currently, to achieve that.

Well, then, you need to provide evidence for this assertion.

1) What is this "high enough quality"? Can you define it?
2) How do you get around the issues of interaural cancellation on center images?
3) How do you provide proper diffuse stimuli that change appropriately with head movement.

These are the technical hurdles.
 

fas42

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Well, then, you need to provide evidence for this assertion.

1) What is this "high enough quality"? Can you define it?
2) How do you get around the issues of interaural cancellation on center images?
3) How do you provide proper diffuse stimuli that change appropriately with head movement.

These are the technical hurdles.
In terms of a technical specification, I can't define "high enough quality" - it appears to hinge on the level, and type, of low level, non-random noise or distortion riding on the waveform - where that impairment originates from is manifold; it tends to be pervavise in most systems, from electrical interference factors, vibration sensitivity, non-ideal power supplies, triboelectric behaviours, electrical connections which are not exemplary, other parastic properties of parts used - I have found that all of these can play a part.

Theoretical cancellations and head movements appear to be all be taken into account by the internal processing of the hearing system, without assistance. A system can manifest "high enough quality" and then drop below that level, simply because some aspect of the system has altered below optimum, for whatever reason; and then be adjusted to reinstate the required quality. This is precisely what happened to me when I first experienced this aural behaviour - the system would slip in and out of the necessary quality level, constantly - so I built up a very strong understanding of the difference in the subjective experience, between strong imaging and then the absence of it.
 

Cosmik

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Not even close. Not even in the dugout, let alone in the actual ballpark. Steinburg and Snow took that apart on 1933. There was an argument about 2 vs. 3 then, with jingoistic advertisers ranting quite maliciously about "you only have two ears", and even then, missing the basic physics of the situation that were already known.

3 channels is rock-bottom MINIMUM for a front soundstage, with no envelopment or depth. Sorry, but that's been firmly established for going on a century now.


So then, you do understand (obviously you do NOT) that different people prefer illusions from their stereo system. Some like direct, some like totally diffuse, some like a mix. That's just one element for starters. I am not going to even describe this in one paragraph.

And for the "two ears" foolishness, our heads move. That alone is a refutation.
I was quite careful in my argument: that two channels has been deemed sufficient "by convention or deliberate design". Notice that I didn't say "because that is what tests have revealed". Or "because listeners prefer it that way". Or "because we only have two ears". The rest of your comment then labours on exactly what I didn't say!
 

Cosmik

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Measure for what? Frequency response of direct signal? Frequency response of diffuse signal? Degree of diffusion of diffuse signal? Direct to diffuse ratio? That as a function of frequency? Distortion? Room interaction (many measurements there), etc.

Remember, two channel playback is a very, very ROUGH approximation of an original soundfield. Steingburg and Snow proved in 1933 (YES, 1933) that ***THREE*** channels were absolutely necessary for proper rendering of the front soundstage, and that 2 was not sufficient.

So we have an illusion made by a flawed system.

Which illusion do you PREFER? Tell me that? Can you describe that in measurements? Just for starters.
I know that in my particular room(s), I don't want omnidirectional, and I don't think I want a super-narrow beam, and I don't want egregiously uneven dispersion against frequency. Large box speakers with more than two ways get it about right in my opinion. Make them active, DSP, linear phase and all that good stuff and I am happy. N.B. Not room correction per se - I am one of those heretics who believes that we hear past the room. As such, the measurements become exceedingly simple.

The point of my earlier post was that this is still the commercial state of the art despite all the talk of listening tests, preferences, diffuse sound fields, measurements. In 1967 people were using 20-20kHz, 0.1% THD systems. Fifty years later, they still are! A few minor tweaks have improved the basic measurements, size and cost that's all. If there's something so much better, people have wasted entire lifetimes not achieving it!
 

Cosmik

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Remember, two channel playback is a very, very ROUGH approximation of an original soundfield. Steingburg and Snow proved in 1933 (YES, 1933) that ***THREE*** channels were absolutely necessary for proper rendering of the front soundstage, and that 2 was not sufficient.

So we have an illusion made by a flawed system.
I make no judgement on who is more correct, but I note that Mr. Linkwitz says:
Far from "being fundamentally flawed" I have found that a 2-channel stereo system is capable of greater spatial realism and believability than n-channel systems typically achieve. Rather than overpowering the brain into surrender to direct sound streams from n-directions for forming a spatial impression, a 2-channel playback cooperates with evolutionary hearing mechanisms, provides a minimum set of spatial cues from two direct streams and from room streams of sound for rendering a frontal auditory scene, which is familiar when appropriately recorded. The perceptual apparatus fills in when cues are missing, but gets distracted when cues won't fit with the formation of a believable mental image and leads to the question: Where am I?.

Can a test in 1933 really "prove" that three channels are necessary? I don't know the details of their experiments, but if it involved sound from loudspeakers, then I doubt they had the FR, distortion and phase characteristics that we have now. With 1933 standards of correlation between the channels then maybe you do need that third speaker..?
 
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Can a test in 1933 really "prove" that three channels are necessary? I don't know the details of their experiments, but if it involved sound from loudspeakers, then I doubt they had the FR, distortion and phase characteristics that we have now.
The test was that of speech (obvious interest of AT&T in that era as the telephone company). The setup of the experiment is on the left. Speakers were placed at the 9 locations and then placed behind curtain. Listeners then voted as to the location of the voices relative to the plane of the curtain:

upload_2017-10-27_22-56-23.png



Start at the bottom with the first box I have highlighted in red. That is what the direct sound was voted as. We see distortion even there (indicated by O vs X). Then look up at the middle diagram for 2-channel which I have highlighted. Configurations 4, 5 and 6 lack depth. The top configuration is for 3 discrete channels and that depth is restored. But error is introduced in the left and right configuration relative to stereo.

Other configurations explore mixing of the discrete channels. This is key as obviously 3-channel mixes can sound bad if all the vocals are dumped in the center channel alone for example. You would get clean sound there but would have shrunk the soundstage. Hope is that some is also put in left and right channels and that the room has side reflections to help with that.

The paper goes into much depth trying to explore what is a pretty complex situation.
 

Blumlein 88

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I wonder how the results might have been different if the 1933 test were done using coincident microphone instead of those spread apart. I suppose from reading the papers they were trying to accomplish soundfield reconstruction. So using single point stereo or 3 channel recordings didn't enter into it at the time.

I have seen listening tests of stereo microphone configurations and their spatial accuracy where crossed figure 8s followed by mid-side recordings resulted in listeners able to most accurately place the performer's location in the recording. Various spaced techniques including spaced pairs of omni's fared much less well. I seem to recall the spaced omnis were the worst.
 

Cosmik

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The test was that of speech (obvious interest of AT&T in that era as the telephone company). The setup of the experiment is on the left. Speakers were placed at the 9 locations and then placed behind curtain. Listeners then voted as to the location of the voices relative to the plane of the curtain:

View attachment 9436


Start at the bottom with the first box I have highlighted in red. That is what the direct sound was voted as. We see distortion even there (indicated by O vs X). Then look up at the middle diagram for 2-channel which I have highlighted. Configurations 4, 5 and 6 lack depth. The top configuration is for 3 discrete channels and that depth is restored. But error is introduced in the left and right configuration relative to stereo.

Other configurations explore mixing of the discrete channels. This is key as obviously 3-channel mixes can sound bad if all the vocals are dumped in the center channel alone for example. You would get clean sound there but would have shrunk the soundstage. Hope is that some is also put in left and right channels and that the room has side reflections to help with that.

The paper goes into much depth trying to explore what is a pretty complex situation.
Thanks Amir, that's great. I notice that it's a pretty specific arrangement of spaced microphones - not a Blumlein pair or other 'coincident' set of microphones.

[Edit: Sorry Blumlein - you said it much better!]
 

Burning Sounds

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Magnepan did some experimentation with 3 channel a few years ago, using a Bryston unit that processed 2 channels into three. IIRC they played some music with the three speakers behind an acoustically transparent curtain to audio journalists who generally raved about what they heard and then some of them felt tricked when Magnepan revealed it was three speakers and not two. Although three six-foot panels may not be practical for most people, Magnepan seem to have successfully used the experiment to develop their motorised on wall speakers aimed at keeping interior designers happy.
 

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Can you give references to research that has determined that internal, ear/brain processing cannot compensate for anomalies in the soundfield, such as interaural cancellation, etc?

Not my job. You claim it exists. You prove that it happens. Your request is similar to asking me to prove "there is no green cheese on the moon".
 

j_j

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My hypothesis is that a sufficiently high enough quality of playback allows this behaviour, and I have already stated that it's extremely difficult, currently, to achieve that. For proper research to be done, enough systems working at that level have to be easily available, and I haven't the facilities for providing that. Evidence from 1933 is valid, when one of the key requirements is that a very high standard of replay accuracy is used - do you think that makes sense?

No, "head in a vice" and "head movement" factors are irrelevant - the brain automatically compensates, with remarkable robustness. The necessary information is provided in two channels, but normal replay corrupts the integrity of the critical, low level detail, which is essential for the brain to do the necessary processing - the illusion never forms, the data is too damaged to allow the processing to occur.


Again, until you can state a falsifiable hypothesis, which the above is not, you are stating nothing but an unsupported belief. This is 'audio science forum'.
 

j_j

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In terms of a technical specification, I can't define "high enough quality" - it appears to hinge on the level, and type, of low level, non-random noise or distortion riding on the waveform - where that impairment originates from is manifold; it tends to be pervavise in most systems, from electrical interference factors, vibration sensitivity, non-ideal power supplies, triboelectric behaviours, electrical connections which are not exemplary, other parastic properties of parts used - I have found that all of these can play a part.

For this to be a ***SCIENTIFIC*** hypothesis, you need to create a falsifiable hypothesis. Again, this is not falsifiable. It isn't even a well-formed statement of any sort.
Theoretical cancellations and head movements appear to be all be taken into account by the internal processing of the hearing system, without assistance.

This is proven false by the 1933 work you obviously have yet to read.
 

j_j

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I was quite careful in my argument: that two channels has been deemed sufficient "by convention or deliberate design". Notice that I didn't say "because that is what tests have revealed". Or "because listeners prefer it that way". Or "because we only have two ears". The rest of your comment then labours on exactly what I didn't say!

I think it's reasonable to say it was "because we can get that on a record". If you look at the history there were many 3-channel recordings in history. Look at the recording for Fantasia, for instance.
 

j_j

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If there's something so much better, people have wasted entire lifetimes not achieving it!

Well, yes. And we knew this in 1933, and then it became the property of advertising and market arguments. 2 channel is surely cheaper.
 

j_j

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I wonder how the results might have been different if the 1933 test were done using coincident microphone instead of those spread apart.

Some abandoned work from the 1990's suggests that NEAR-coincident works even better. Coincident does not provide a wide listening area or proper perspective as the listener's head moves.
 

j_j

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The test was that of speech (obvious interest of AT&T in that era as the telephone company).

Having seen the original data, there were a variety of stimulii, but speech provided results consistent with the other sounds.
 

j_j

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I make no judgement on who is more correct, but I note that Mr. Linkwitz says:

Seigfried and I have indeed had a similar discussion. He is responding based on most of the material presently available. For that, given that the production is very wrong for proper spatialization, he's right.

The hints to "right" come in the 1933 paper and in later work on ITD and ILD understanding from the 1950's.

I'm hoping he will get to the spatial audio conference in Redmond next summer.
 

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Seigfried and I have indeed had a similar discussion. He is responding based on most of the material presently available. For that, given that the production is very wrong for proper spatialization, he's right.

The hints to "right" come in the 1933 paper and in later work on ITD and ILD understanding from the 1950's.

I'm hoping he will get to the spatial audio conference in Redmond next summer.

BTW, what's your opinion on two channel omnis, JJ? I've been a lone proponent of that kind of speaker here. For me, spatialization is one of the key reasons why I like them.
 
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