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The quantification of stereo imaging

LDKTA

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Having a system that has precise stereo imaging is absolutely a thing and exists.

From my experience its a room and placement thing, not a speaker or equipment thing. All speakers can pull the neat trick of having a stereo image. I've noticed that the horns on my JBL 4367 offer a more 'hanging in the air' sort of voice then other speakers I have owned. It's kind of a spooky thing, like the voice is hanging in the air in front of you. You can close your eyes and hear the voice move, again, depending on the recording.

I love the track Paultalk from the album Peter, Paul & Mary: Live in Japan 1967. There is a strong sense of venue space in the recording and as both artists, Paul and his translator talk on stage you can hear their placements, as well as when Paul starts moving around. You can tell when he moves the mic closer to his mouth, and when he's stepped off to the side. You can hear and feel the rumble of the footsteps on the stage as they walk around.

https://tidal.com/browse/track/18236272

My 708s do the same. Great directivity from a waveguide. It can certainly be spooky... but so lovely.
 

majingotan

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Any perceived effect of depth, width or height is purely an artifact of the loudspeakers, the loudspeakers interaction with room reflections (delay), and response anomalies mimicking the ears spectral modification that encodes the source (height, width and depth). A cool illusion nonetheless.

I'd really want to test this in an anechoic chamber. Would I finally hear the true sound stage? Then again, my speakers when listened 2 feet away from tweeters can mimic a large concert hall if the recording is done well.
 
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dshreter

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The most accurate (two channel) stereo playback system is one that puts all the soundstage at a constant height. Any perceived effect of depth, width or height is purely an artifact of the loudspeakers, the loudspeakers interaction with room reflections (delay), and response anomalies mimicking the ears spectral modification that encodes the source (height, width and depth). A cool illusion nonetheless.

I find it believable that there can be three dimensional attributes captured in a stereo recording. With the complexity of phase interactions, it’s believable that there can information in a recording indicative of the Y and Z axes. With binaural recordings, while the effect is best realized with headphones, to me they are strong evidence that a 3D soundstage is possible to capture in a recording.

I would still prefer to focus on imaging along the singular x axis and it’s measurability, then build from that point.
 
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dshreter

dshreter

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Griesinger has done some very excellent work on localization and attention (his interest is specifically in concert hall acoustics).
I like this line of thinking. Working back from how aural localization is achieved should help with identifying measurable parameters for how well a system is achieving localization or imaging.

This page seems to have some good information on the topic:
http://acousticslab.org/psychoacoustics/PMFiles/Module07a.htm
We localize sound based on phase (period-related time), intensity level, and spectral differences between the portions of the sound arriving at each ear. Interaural differences in arrival time (phase) and intensity constitute the most important sound localization cues. The theory outlining their contribution to sound localization judgments is referred to as the duplex theory of sound localization and was introduced by Lord Rayleigh (1877-1907).

Phase, intensity, and spectral composition are all measurable so we have a starting point to make measurements! Interestingly, the effect is achieved differently based upon frequency, with phase being most important for low frequency sounds and variation in intensity for high frequency.

So what we would want to test is a system’s ability to achieve the appropriate phase differential from ear to ear, and the ability to achieve the appropriate intensity differential from ear to ear. I really don’t know what to make of spectral shift from ear to ear, and this seems like it would be the most complex of the three measures to evaluate.

Does anyone have ideas for how these concepts could be measured using a toolkit like REW?
 
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audiophile

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It’s measurable. By measuring distances from the speakers to the rear and side walls as well as to the listening position.
Here’s a calculator that uses Cardas method of speaker placement:
Speakers placed along the short wall
Speakers placed along the long wall

It provides rough estimations for the best speakers and chair placement in a room, which results in the most holographic 3D presentation of music on almost any recording. It works for any speaker of traditional design, doesn’t matter if it’s a $200 or $10000 speaker.

After the optimal position is found you can play Jennifer Warnes’ “Bird on a Wire”, close your eyes and see this very clearly:

0159DB16-DAD4-45C9-85DD-9CE543C8755B.png

This is an exact instruments layout showing how this song was mixed. Notice that the whole soundstage is located behind the speakers, this is how it should be when done properly.

Unfortunately, most people won’t be able to use Cardas placement in their living rooms. I’m lucky to have a dedicated listening space, built around the speakers. But even if you can’t use this positioning on a permanent basis, I strongly suggest at least trying it temporarily and see what you’re missing. There is a good chance you’ll be blown away, especially if you never heard true soundstage “depth” before.
 
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restorer-john

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After the optimal position is found you can play Jennifer Warnes’ “Bird on a Wire”, close your eyes and see this very clearly:

Ah, the classic audiophile and HiFi salesmen's goto recording. What about The Hunter album by Jennifer Warnes? It's a great disc to sell HiFi to, as well.

The example above, the drum kit has been torn apart and the saxophone player is in between- hardly representative of a real situation. More like the guy on the mixer had too many mics and too many pan pots if you ask me. And yes, I love Jennifer Warnes, but not so much that old chestnut of a recording. I guess I heard it too often.

Depth and height in live recordings is something amazing. Usually achieved with a crossed pair of omnis from out in the audience or perhaps coincident cardioids closer to the action. But I'm no expert, I just know it when I hear it, and on 90% of recordings, it's simply not there.
 

audiophile

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Ah, the classic audiophile and HiFi salesmen's goto recording.
The only reason to use this specific song is because we have the instruments layout for it. I’d gladly use other examples if similar information was available for them.

The example above, the drum kit has been torn apart and the saxophone player is in between- hardly representative of a real situation.
So what? That’s not the point. Do you hear the instruments coming from their locations as shown on the picture? That’s the question to ask yourself to verify if your system setup correctly.
 

restorer-john

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The only reason to use this specific song is because we have the instruments layout for it. I’d gladly use other examples if similar information was available for them.

I wasn't criticizing the choice, just the endless analysis of that particular disc done by 'experts' for several decades now. That graphic has done the rounds.

As I said, don't get me wrong, a good recording is a reference, but Famous Blue Raincoat was usurped by literally hundreds of better recordings even in the 90s.

And yes, I have several copies myself... ;)
 

audiophile

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I wasn't criticizing the choice, just the endless analysis of that particular disc done by 'experts' for several decades now. That graphic has done the rounds.
I know what you mean. I’m bored as hell with this record too. Listened to it too much while tweaking the system, although there were times when I liked it :)
 

Wombat

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It seems like an artificial construct to me. How can that be meaningful? Like Yello's The Race. Impressive but not real(istic). Sound effect stuff.
 

Juhazi

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Imaging is much more about the room and positioning than the speakers. I can't see any point trying to create quantification to it.
Besides this, some people prefer a more diffuse and wide soundfield, which often also gives wider listening area (like myself, I'm not a mixing/mastering engineer)

We can make an educated guess of how "tight" imaging we can get from a pair of stereo speakers. Directivity performance tells that for the speaker (the more narrow beam, the better imaging), but positioning and room reflectiveness is more complicated. Placing speakers on the long wall far from sidewalls helps, Cardas setup is good guideline.

http://www.aes.org/e-lib/browse.cfm?elib=7671
https://www.researchgate.net/public..._sound_quality_-_a_review_of_existing_studies
http://www.linkwitzlab.com/Constant_directivity_louds.htm
 

audiophile

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Impressive but not real(istic). Sound effect stuff.
Again, this is not the point when setting up a system to reproduce wide and deep soundstage. Realistic or not you should hear the instruments coming from their exact places as shown on the drawing.
 

FrantzM

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What we hear at home on our stereo system and marvel at, our sacred and so-loved "imaging", is not what I perceive in most venues.

With my eyes, ears and brain, I can process and manage to hear and find where (some?) of the instruments are .. Without my eyes and an intellectual effort, I hear a big, blob of sound in all of the concert hall in which I have gone (several)... In much smaller settings say a Jazz trio in a small club and seating up close, I can make of sound coming from the different instruments .. even with my eyes closed .. add a few more instruments, a sextet for exemple and the blob returns...
I do like the imaging effect and am somewhat attracted by speakers that present that acoustical "image" well. In my experience, all speakers do not acquit themselves equally well of such...
Measurements that would allow us to know why and or a way to measure the level of imaging presented by a speaker would be welcome. Other will interject, I do not know of such metric or at the very least a series measurements that would help derive some metric or scale.


P.S. Long time audiophiles may recall a speaker that imaged in a very spooky way ( did a few other things well too...): the Spica TC-50. With reasonable care and placement it was easy for this little speakers to completely disappear. I l have fond memory of this one; back when I was in college these were one of the few so called "audiophile" speakers my pocket could afford (second hand of course) and that could live in a small living room. Those speakers disappeared in a way few speakers I have heard do ... One the anecdotal things that attract me to Siegfried Linkwitz is how they are said to disappear within the soundfield and image extremely well. Something I do favor in spite of Live Music music experience being presented to me mostly as a big blob :D
 

Wombat

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Again, this is not the point when setting up a system to reproduce wide and deep soundstage. Realistic or not you should hear the instruments coming from their exact places as shown on the drawing.

And this then is optimum for all recordings?

I was disabused of the value of the general applicability of soundstage when, many years ago, I realised that most recordings are a cut and paste of individual artists/instruments in an unknown(to me) spatial relationship. Isolation booths, different studios, various cities and countries - different times and spaces. At root, an assortment of isolated/individual 'tracks' manipulated into a 'performance' at a mixing/mastering desk.
 
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audiophile

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And this then is optimum for all recordings?
I think so. It’s about accurate reproduction of the soundstage as it was done by the mixing engineer. I too prefer recordings which are mixed naturally, close to a live performance. They all sound excellent in my room and project very life-like holographic soundstage.
 

Wombat

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I think so. It’s about accurate reproduction of the soundstage as it was done by the mixing engineer. I too prefer recordings which are mixed naturally, close to a live performance. They all sound excellent in my room and project very life-like holographic soundstage.

I get the impression that you are happy with an artificial construct if it meets your subjective expectation of soundstage.
 

fredoamigo

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The mixing engineer is not often at the scene of the initial recording so he will try to transcribe, embellish, or even modify the initial sound scene with spatialization, selection of frequencies used to place each instrument in the audio spectrum, reverbs, delays, compression, and other more sophisticated processing.
Some mixes are very impressive like the famous Roger Waters - Amused to Death perfect sense part1
many of them have nothing to do with the reality of the initial sound recording and you end up with a drum set that is too big or a saxophone that is too big ...
sometimes we are in the circle of confusion, at least more in the realm of illusionism than reality. what do we expect from high fidelity ? the pleasure of an artificial 3d sound stage or the raw reality of a sound recording ?


 

thewas

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As partially said in above posts
a) imaging depends more on the speaker placement and room acoustics then speakers themselves
b) less reflections like in from a less reverberant room and/or a more directional speaker bring usually the image closer to the listener and make it sharper but also smaller (an extreme example are headphones)
c) from speaker side of view, a less good imaging is often due to nearby diffraction problems https://heissmann-acoustics.de/en/kantendiffraktion-sekundaerschallquellen-treiberanordnun/ (which can also be visually seen with previously shown acoustical camera - had the fun to use one at work) and/or higher pair deviations
d) most music and imaging is just a product of mixing where the different instruments are virtually panned to their positions
e) stereophony as an underactuated system (2 signals try to create a 3 dimensional image) is a compromise with big deficits and only works quite ok due to our previous auditive experiences and with trickery like the famous "Amused to death" https://en.wikipedia.org/wiki/QSound
 
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Hipper

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It seems there are a number of factors that contribute to good imaging:

1. The recording.
2. The speakers.
3. The room, its contents, and speaker/chair positioning in that room.
4. Our brain.

Within reason, most stereo recordings will give some sort of image if speakers are reasonably well set up. Our brain - psychoacoustics - seems variable in quality and experience and training can help but the phantom image appears to be a fortunate quirk of stereo listening which has no obvious evolutionary reason - does it help us survive (I think this applies to a stereo photographic image too).

What the OP is asking for is some quality/quantity that we can measure (using Room EQ Wizard for example) in our rooms, namely, once we've set up the room, speakers and listening chair as best we can.

I would have thought these measurements would be on the lines of:

1. Both speakers have exactly equal performance.
2. Some measurable qualities like phase, frequency response, direct sound and off axis response, dispersion, degree of reflections.

Before we know what these measurements are we need to understand what qualities are required, or are detrimental, to the formation of the phantom image.

One thing seems obvious - reflections are not necessary. We can get a phantom image with headphones where there are no reflections. I suspect though that reflections can damage the image, but I can't say for sure.

Another factor might be interaural crosstalk (where the left ear hears the sound not only from the left speaker but the right too). We don't get interaural crosstalk on headphones, and even if we use a processor that gives us this, or we remove it from speaker listening with ambiophonics, we still get a phantom image. It's possible these things can enhance or reduce the image - I don't know.

This article by Sean Olive from 2009 talks of desired speaker qualities:

https://seanolive.blogspot.com/2009/01/what-loudspeaker-specifications-are.html

"1.The perception of loudspeaker sound quality is dominated by linear distortions, which can be accurately quantified and predicted using a set of comprehensive anechoic frequency response measurements (see my previous posting here)

2. Both trained and untrained listeners tend to prefer the most accurate loudspeakers when measured under controlled double-blind listening conditions (see this article here).

3. The relationship between perception and measurement of nonlinear distortions is less well understood and needs further research. Popular specifications like Total Harmonic Distortion (THD) and Intermodulation Distortion (IM) do not accurately reflect the distortion’s audibility and effect on the perceived sound quality of the loudspeaker.

4. Current industry loudspeaker specifications are woefully inadequate in characterizing the sound quality of the loudspeaker. The commonly quoted “20 Hz - 20 kHz , +- 3 dB” single-curve specification is a good example. Floyd Toole made the observation that there is more useful performance information on the side of a tire (see tire below) compared to what’s currently found on most loudspeaker spec sheets (see Floyd's new book "Sound Reproduction")."

The tests showed that the preference was for accurate on axis frequency response and smooth off axis with smooth phase. They also preferred some reflections. Even this is controversial as electrostats for example would measure poorly but many like them. I assume electrostats produce a phantom image so perhaps the above requirements aren't essential for our purposes, or more likely, there's something more.

I suggest it's more about speaker positioning. I know that is the case with photographic images. Take a pair of stereo images, use a stereoscope then line up the images until the stereo image appears. This can be difficult but when you hit the spot (there's just one), ships' masts come up and poke you in the eye! Perhaps stereo music is like that.

If that's the case, it is not about measurements of the speakers but exact positioning. I would think that what is needed is some recording that will produce signals coming out of the speaker which will allow us to best align the speakers. Of course some attempts (Stereophile, Chesky) have been made at this But I've never found them particularly helpful. Jim Smith in his book 'Get Better Sound' tries to help with suggestions of what you should hear on particular music CDs if your set up is right, and he is trying to produce some new product called 'Through the Sound Barrier' which may go further.
 

majingotan

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index.php

This is an exact instruments layout showing how this song was mixed. Notice that the whole soundstage is located behind the speakers, this is how it should be when done properly

This is exactly why I don’t use headphones for my home listening. None of them can replicate this imaging and sound stage that I hear from my near field speakers.

BTW, the way sound is reproduced as depicted from the photo is most easily achieved by listening 2 feet away from the tweeters and at perfect triangular position. Obviously not all the instruments in the recordings will position themselves the way the photo depicts them but the key is that the sound is emitted in a way that you’re a few rows back. Like many have said, it’s not dependent on speaker but room correction and placement.
 
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