What makes the sensation of "sound stage"?

[restorer-john]

Nope ...

... and nope.

I said 2D for simplification purpose, but in reality, it's only 1D.
Let's introduce some similarity with geometry.
If you draw a line between 2 points, you have 1D (one axis), as in our case (2 point sources), so you can locate a sound from 100% left to 100% right. That is if you were in a 100% anechoic environment.
Depth (2D) needs a second axis to become real.
3D needs to introduce a third axis which is height.

Back to 2D and 3D: from lack of real additional sound source(s)(read axes), we have wall, floor and ceiling reflections, but they have nothing in common neither with real sources, nor with what the sound engineer did to give us some psychoacoutic clues for an illusion of depth.
Reflections are an altered image of our 2 primary sound sources. Think of it as 2 lights in a mirror box with black floor and ceiling. you could see multiple images of your light sources, but it is in fact the same source. We need additional information from behind, not an altered and delayed copy of the front (reflection from the wall behind the sound sources).
I said altered copies because:
- wall absorption properties alter the spectrum of the incoming sound from the speaker (same for front and ceiling)
- the spectrum sent by the speaker varies according to its directivity (except for some true omnidirectional speakers)

Oh,and did I mention comb filtering due to interference between 2 coherent sources ?

Let's face the truth: recorded music is a projection performed by the sound engineer of a 3D environment to a simple line (1D) in front of you.
Photography is a 2D projection of a 3D environment, where depth is also an illusion, depending on the skills of the photographer.
Ah the skills of the recording engineer ...

Nope.

Stereo means 3D. Comes from the Greek word "stereos" meaning solid.

Stereo reproduction (audio) is all about 3 dimensions, always was, always will be. Otherwise it's just 2 channel monophonic.

 

[richard12511]

Nope.

Stereo means 3D. Comes from the Greek word "stereos" meaning solid.

Stereo reporduction (audio) is all about 3 dimensions, always was, always will be. Otherwise it's just 2 channel monophonic.

I think there's a distinction between what it physically is, and how it sounds. I think both of y'all are correct, but talking about different things.

Technically, and mathematically, he's correct. 2 speakers treated as points is just 1 dimension, and that's dictated by the physics/mathematics. You only ever need one dimension to fully describe their relative position. Imagine you have a lazer that can pass through objects. You would only need 1 such lazer to hit both speakers. It's impossible to have anything more than 1 dimension with just 2 points in space. Kinda weird, but I think the key to understanding it is understanding the difference between points, lines, and planes, and that points are 0 dimensional constructs. Lines drawn through the points define your dimensions. Given a sheet of paper with 2 points on it, what is the minimum number of lines you need to draw so that the line passes through both points? The answer to that question gives you the number of dimensions.

Practically, though, I get what you're saying. 2 speakers can sound fully 3 dimensional, with sounds coming from all directions.

Also might be important to distinguish between the technical sound they can produce, and the actual sound that comes out and reaches your ears. While technically just 1 dimensional, the 2 speakers are 3 dimensional objects themselves, and they are playing into a 3 dimensional world, so the sound that you hear really is 3 dimensional.

Another important distinction I would say is that while the engineer technically only has 1 spatial dimension(L) to work with, he actually has 2 dimensions in reality, with the other one being time.

 

[Chrispy]

Stereo isn't just 2.0....

 

[richard12511]

Stereo isn't just 2.0....

Do you mean 2.1, or something else? To be clear I was talking specifically about 2 discrete channels playing into a room. Such a configuration has one spatial dimension and one non spatial dimension, but produces 3D sound.

 

[Emlin]

I think there's a distinction between what it physically is, and how it sounds. I think both of y'all are correct, but talking about different things.

Technically, and mathematically, he's correct. 2 speakers treated as points is just 1 dimension, and that's dictated by the physics/mathematics. You only ever need one dimension to fully describe their relative position. Imagine you have a lazer that can pass through objects. You would only need 1 such lazer to hit both speakers. It's impossible to have anything more than 1 dimension with just 2 points in space. Kinda weird, but I think the key to understanding it is understanding the difference between points, lines, and planes, and that points are 0 dimensional constructs. Lines drawn through the points define your dimensions. Given a sheet of paper with 2 points on it, what is the minimum number of lines you need to draw so that the line passes through both points? The answer to that question gives you the number of dimensions.

Practically, though, I get what you're saying. 2 speakers can sound fully 3 dimensional, with sounds coming from all directions.

Also might be important to distinguish between the technical sound they can produce, and the actual sound that comes out and reaches your ears. While technically just 1 dimensional, the 2 speakers are 3 dimensional objects themselves, and they are playing into a 3 dimensional world, so the sound that you hear really is 3 dimensional.

Another important distinction I would say is that while the engineer technically only has 1 spatial dimension(L) to work with, he actually has 2 dimensions in reality, with the other one being time.

Once again I'm being pedantic, but stereo does mean 3D. And lazer refers to a tree, whereas laser doesn't.

 

[richard12511]

Once again I'm being pedantic, but stereo does mean 3D. And lazer refers to a tree, whereas laser doesn't.

And I never disputed that, which is why I said both are correct. I’m not disputing the word meaning, I’m disputing that 2 points can ever be more than 1 dimensional.

Im also agreeing that stereo produces a 3 dimension sound.

Btw, tping on a phone, so don’t be surprised to more fat finger mistakes. Kinda lame to pick on spelling mistakes. Do you really think that added to the value of your post? I agreed with the rest of it.

 

[Chrispy]

Do you mean 2.1, or something else? To be clear I was talking specifically about 2 discrete channels playing into a room. Such a configuration has one spatial dimension and one non spatial dimension, but produces 3D sound.

Just meant that stereo encompasses not just 2.0/2.1 but all the surround modes as well, they're just other ways of going about getting a stereo image (which is essentially the 3d thing)

 

[richard12511]

Just meant that stereo encompasses not just 2.0/2.1 but all the surround modes as well, they're just other ways of going about getting a stereo image (which is essentially the 3d thing)

Gotcha. Yeah then I don’t mean stereo. My point applies specifically to just 2 speakers. I thought we were debating whether or not 2 speakers can be 3D, but I see now that some of y’all were debating the word definition. I got nothing to add there, at least not without googling.

Edit: @Emlin, @Chrispy I just reread my post, and I never even used the word stereo(I could have sworn I was careful not to), so I'm not sure why y'all thought I did.

My point in that post was that although @restorer-john is correct, I thought the person he was talking to was talking about something completely different, which was where the disagreement was coming from.

 

[Destination: Moon]

Isn't the existence of anything other than 3 dimensional objects purely theoretical? Any physical object or rendering exists in 3 dimensions. Even if it's one molecule in size, it still has 3 measurable dimensions

 

[Wombat]

Soundstage = main signal + its room echo interference/interaction summation impinging on a point in the room space. A manipulatable and non-verifiable(from the recorded information) effect - that some find likeable.

 

[restorer-john]

Isn't the existence of anything other than 3 dimensional objects purely theoretical? Any physical object or rendering exists in 3 dimensions. Even if it's one molecule in size, it still has 3 measurable dimensions

What about time (4th dimension)?

 

[richard12511]

Isn't the existence of anything other than 3 dimensional objects purely theoretical? Any physical object or rendering exists in 3 dimensions. Even if it's one molecule in size, it still has 3 measurable dimensions

Yep, even a single speaker produces a 3d soundstage when it plays into a 3 dimensional world. 0 dimensional points (afaik) don't exist in reality.

I was just trying to clarify that both fmplayer and John were technically correct, but just talking about different things, at least from what I could tell. I feel I just added to the confusion. Sorry for that.

 

[Pennyless Audiophile]

I would suggest keeping both if you have the space. I have 5 active systems, including one with 4 zones and one for the whole house, but I still hang on to several 4-6 pairs of other speakers in case I want to spice it up.

Basically a harem...

 

[oursmagenta]

Let's make that straight:
1. It's impossible to make 3D from 2D (in our case stereophony), there's something missing. So it's all a matter of psychoacoustics.
2. Sound is recorded multimiked most of the time.
Mics are close to the musicians and the frequency spectrum is not the same compared to a musician farther away (highs are more absorbed by atmosphere than mids for example). For those who might think that recording with more distant microphones solves the 3D problem, it just mixes more reverberation from the room (Add soe flavour of the acoustics at the cost of clarity).
3. The recording engineer is key

Fom the recording engineer's perspective, point is to gel everything from a 3D sound into the 2 channel (2D remember ?) mix. Making something sound more distant is obtained by eq'ing down the highs of a track, eventually adding some delay. In other words, his job is to prepare the stereo signal, and make an illusion because the brain cannot do its job with recorded (2D) music.
Brain processes 3D sound, not 2D.
For those who doubt, compare a debate in real life and a debate on TV. In the former case, you understand everybody clearly, in the latter, it's just a big mess.
Remember also that the sound engineers listens either nearfield with small monitors or farfield with big soffit mounted speakers. In either case, there is little to no influence of speaker placement.

Mastering engineers have another point of view, closer to ours as to room environment influence.
From our perspective, room influence is key. Speakers far away from the walls make for an environment that resembles the recording engineers', where reflections don't mess the signal. For the others, DSP based cardioid directivity speakers (Dutch & Dutch,Kii Audio) aim at lowering room influence. For the vast majority of us, room reflections superimpose to 2D sound, and at best illusion is credible.
Speaker time coherence doesn't hurt of course, but incoherent spectrum between direct and reflected sound is a challenge for the brain to process those sometimes contradictory clues.

Huh. We have two ears. Remember that 3D cues are coming from the diffraction/reflection of the incoming sound sources w.r.t your body/head/ears etc... and time delays.

So technically with ultra directive speakers directed at your ears with a custom transfer function that would be variation of your HRTF we should be able to do 3D.

One approach would be to fake headphones + HRTF with ultra directive speakers + a sort of HRTF.
I'm not saying that it would be practical nor desirable, it would be actually totally dumb to do that.

Another one would be to try to reproduce as accurately as possible the pressure field around the listener with two speakers (it would only work for one given listening position of course).

The biggest issue would be to manage the cross-feed correctly (the fact that your left ears has also access to the sound of the right speaker, and vice versa) and optimize for it.

And my guess is that the best recording are actually doing this optimization not algorithmically but with the experience/skill of the mastering/mixing engineers.

 

[Destination: Moon]

What about time (4th dimension)?

https://phys.org/news/2012-04-physicists-abolish-fourth-dimension-space.html

 

[Blaspheme]

Yep, even a single speaker produces a 3d soundstage when it plays into a 3 dimensional world. 0 dimensional points (afaik) don't exist in reality.

I was just trying to clarify that both fmplayer and John were technically correct, but just talking about different things, at least from what I could tell. I feel I just added to the confusion. Sorry for that.

Semantics are hard.

The way I look at it, you need x,y to locate two points on a plane, so 2 dimensions. You need x,y,z to locate two points in a volume, so three dimensions. You can draw a line between the two points. You can consider that line as located on a plane, or within a volume, hence the confusion (same with a point, of course).

Personally, I'm with restorer-john on this. Stereo microscopes are very cool.

 

[richard12511]

Semantics are hard.

The way I look at it, you need x,y to locate two points on a plane, so 2 dimensions. You need x,y,z to locate two points in a volume, so three dimensions. .

Good thinking, and I almost clarified this point in my previous post, but I felt I was already getting too far out into the physics weeds that don't really matter for audio. Important to not confuse the "points" that I am talking about with "coordinates".

A plane(3 points) is indeed 2 dimensions, and the fact that you can identify any point on that plane with 2 coordinates(x,y) is a great way to think about it, as you mention. Similarly, you can fully define the location of any object on a line(2 points) with just 1 coordinate(x), hence it(and 2 speakers) being just 1 dimension.

There was a really great youtube video I watched 5+ years ago describing points, lines, and planes as a means to understand the 11 dimensions. I looked for it a few days ago, but couldn't find it. There was one that was similar, but no where near as good as the one I remember.

 

[RobL]

Interesting discussion...manufactured illusion or encoded effect? Is it possible that there are some localization clues (reflections etc.) captured by the mic’s that our brain can decode?
I’m sure that the engineers have tools available as well to enhance the effect. Listen to “Dogs” on Roger Water’s In The Flesh album. You will swear the barking is coming from behind you!

 

[audio2design]

No, both are similar size and design. One is sealed with a large passive radiator and the other is ported to the rear.

One is definitely more directional. Interestingly, the directional one seems to have the more district sound stage. The other is far less directional and open sounding, yet the music doesn't sound as 3 dimensional? Does that make sense?

Yes completely makes sense. Going to guess your room is not overly treated, and the more directional speaker has less interaction with your room, at least with respect to power of first reflections which can seriously impact your ability to extract location information that may be buried in the source material.

 

[Destination: Moon]

Yes completely makes sense. Going to guess your room is not overly treated, and the more directional speaker has less interaction with your room, at least with respect to power of first reflections which can seriously impact your ability to extract location information that may be buried in the source material.

Our room is exceptionally non reflective. Soft furniture and very heavy drapery on all windows. Whatever it is it's an interesting difference