Is soundstage DEPTH a myth?

Much of what sense of depth you perceive has to do with how a recording was made. 

We hear with two ears that are for all practical purposes are the same distance from the front of the stage.  They are also the same distance from the rear of the stage.  The space between our ears accounts for the difference in arrival time as well as the difference in intensity of sound reaching each ear.  This works very well in helping us locate (left to right) the source of sound.  What helps us differentiate what sounds are coming from the front of the stage vs. the rear, is the proportion of direct to reflected sound as well as the loudness.  In a concert hall, the closer we sit to the front of the stage, the greater the difference  we will perceive between strings and woodwinds as an example.  When we sit more toward the back of the concert hall, the greater the amount of reflected sound vs. direct sound reaches us and so the depth of the orchestra gets flattened out. 

So back to how a recording was made:  If many microphones are placed throughout the orchestra, not only will the sounds of say, the horns reach their mics at the same time as the sounds of the strings reach their mics, the pickup of each of those sections will contain roughly the same proportion of direct vs. reflected sound.  While it is possible to delay signal coming from mics toward the rear of the orchestra, there is not much that can be done to alter the proportion of direct to reflected sound in any sort of a natural way.  This is why these kinds of recordings sound so flat from a depth perspective.  It's kind of like a cardboard cutout of an orchestra.  Everything sounds intimate, but not anything like it sounds in a concert hall.  If you listen to very early stereo recordings made by Lewis Layton or Bob Fine for RCA and Mercury respectively, you will hear all the natural depth of the orchestra from the best seat in the house.  Why?  They used only two or three mics and placed them very carefully.  Many of the Telarc and Chandos recordings were made using similar techniques.

Recordings of rock and jazz and pop music are typically (not always) made using close mic techniques.  Seven mics on a drum set is not unusual.  Very intimate sound, but nothing approaching natural sounding.

@dinov Spot on. After a bit of upgrading (more than a bit) I could have sworn all of a sudden music was playing behind as well as in front of my listing chair. That's the very definition of holographic soundstage. 

Soundstage depth mostly depends on recording and mixing quality rather than your equipment. 

I had a recording studio for 10 years and I can assure you that to a recording engineer, soundstage depth is "a thing." Depending on the band and the source material, I worked very hard to create an illusion of soundstage depth using several well known techniques.

Creating the illusion that some instruments and voices are behind others involves using carefully structured reverb and delay on each track besides volume differences and EQ (not to mention how the instrument was actually recorded). The engineer can vary the timing of a delayed reverb, the length of the tail, the frequency response of the reverb, and other cues to make it sound like some instruments are further back than others. Most engineers would be very disappointed to hear someone say that there was no soundstage depth to their recordings.

If you read the recording notes of many modern classical recordings you will see that the engineer uses several microphones placed near the orchestra and various places in the hall. The mixing engineer then can manipulate these individual tracks to create the illusion that you are sitting in that hall. I've got some classical records that have caused people unfamiliar with audiophile sound to sit there gaping in awe. One friend exclaimed loudly, "How does it do that!!!?"

In contrast, some genres like hardcore want zero depth. They want the sound to be in your face, in a flat plane between the speakers. Obviously, this demands a different set of recording and mixing techniques. I can tell you from experience, it's not easy to get that sound.

I'll give you an old example to test. Santana's first album has a very good soundstage with the illusion of depth. If you hear a flat soundstage where all the instruments sound like they are in the same plane my advice is to work on your system. If you haven't been to an audio show I would suggest that you start there. You will definitely hear some systems and recordings that are downright spooky in how they create the illusion of depth.

Here is a relatively quick test to see if you can hear this phenomenon. Move your speakers out into the room and move your listening seat if needed so that you are listening in a very nearfield setup. Put the speakers about 3 or 5 feet in front of you (experiment) and sit exactly between them. You should get an effect approaching that of wearing headphones. The sound should be "holographic." Hopefully you should hear the illusion of depth on good quality recordings. Once you hear this you will "get it." Too often audiophiles constrain themselves with speaker setup that prevents achieving a deep soundstage. For an afternoon, forget WAF or any other constraint and play with your speaker and listening location. Maybe you can't leave everything in the optimal listening position but you you will know what you are shooting for and you can try to get it as close as possible.

For me the illusion of depth is one of the most thrilling aspects of this hobby. Sometimes when I'm listening to a favorite well recorded title I just smile and shake my head. I've heard this thousands of times and it still blows me away.

@hypoman 

Your comments are among the most relevant to the issue.  Many pop/rock recordings, and other studio recordings, don't have genuine depth.  Well-recorded orchestral recordings are perhaps the best for hearing depth, partly because there is more physical depth to an orchestra than to smaller groups.

I suppose you also have to have some level of quality in your electronics--there needs to be enough transparency to hear the depth clearly, and mid-fi electronics may lack that.