Blue or red pill?

[adamdea]

7 hours ago, lmitche said:

So the Superposition Principle works differently for microphones then eardrums? 

 

It is perfectly clear from listening that, for lack of a better term, "height cues" are captured by microphones and are reproduced by most recordings. Sure, microphone position matters, but usually, no always, height information is there.

 

I am happy to agree to disagree in this one.

I think you are missing an important distinction here. There are things in a recording which (some) people will interpret as height. That is not the same as saying that the recording has encoded actual height information. There isn’t really and way for it to do that except possibly using dummy heads, but even then they would only work using headphones and even then only to the extent that they match your personal hrtf. 

However, given the way your brain decodes height information (and potential quirks of gap filling) it may interpret certain spectral patterns as height. This effect can’t be encoded to match actual height by an ordinary mikes and is not consistent across listeners. The sound has to reach the ears from the right angle in order for your head to create the right spectral patterns for it to work properly. 

[Audiophile Neuroscience]

14 minutes ago, mansr said:

Two microphones in, say, a standard XY stereo configuration clearly separate sounds on a left/right axis. This is so blatantly obvious that I neglected to explicitly mention it in that post you refer it. Picture a sound source at centre, some distance directly in front of such a microphone pair. The sound arrives at both microphones 45° off-axis, giving equal response from both. If the source moves sideways, it comes closer to the axis of one microphone and further off-axis of the other. As these are cardioids, their responses will now be unequal. The lateral position is thus readily recorded. I doubt anyone disputes this.

 

Now let the sound source move upwards from its original centre position. As it rises, the source moves further off-axis, by equal amounts for both microphones. The resulting response is somewhat diminished but otherwise unchanged. Due to symmetry, the exact same difference obviously is produced if the sound source moves down rather than up. Moving the sound source, still centred, away from the microphones again drops the amplitude of the response. From the recorded signals, there is no way of determining from which point in a plane bisecting the angle between the microphones the sound originated. For an off-centre source, the geometry becomes a little more complicated and dependent on the exact pattern of the microphones, but in general, for any point in space, there are infinite other points where a sound source would produce the same relative response from the microphones. Mathematically speaking, we are dealing with a projection of three dimensions onto two, and this always entails loss of information.

 

The reason we are able to locate sounds is that our ears are not symmetrical. Their frequency response varies with direction, and the resulting change in sound as our head moves, even by a small amount, helps us deduce the location of the source. For this reason, locating the source of a pure tone can be quite difficult compared to a spread of frequencies. In fact, sirens on emergency vehicles have in many places been altered to take this into account. Likewise, electric carts seen in places like airports often emit bursts of pink-ish noise as alerts since this is more easily localised than a tone.

Thanks Mans for the explanation!

[semente]

20 minutes ago, STC said:

Ok. Now I admit I didn’t read your link. I always thought both meant the same thing. 

 

I think I should alert oxford dictionary to include audiophile’s jargons too. 

 

[STC]

Re: Height in stereo

 

It is my understanding that height is not possible with stereo but in ATD the voice of god indeed sounded as if coming from above with standard 2 channel stereo. 

 

On some occasions, I did perceive height but didn’t bother to find out the reason. Now that I am using a very tall speakers which is almost twice my height from sitting position I do perceive height more often. 

 

OTOH, it is possible that we are using our prior encoded knowledge encoded in is to place height. In one classical recordings, there was some flying birds chirping and I was very sure it sound at hear level before but when I don’t listen but just enjoy the music the chirps appear to be coming from above. 

 

This is purely my observation.  

 

[mansr]

41 minutes ago, mansr said:

Mathematically speaking, we are dealing with a projection of three dimensions onto two, and this always entails loss of information.

Slight correction. Although there are two microphones, their responses are not independent. The projection is onto one dimension, the left/right axis, although it ends up encoded using two values. This might seem wasteful, but we anyway need two values in order to represent both position and amplitude. Using a mid/side microphone configuration, their outputs more closely resemble this separation. Calculating the sum and difference of the XY signals gives a similar result.

[STC]

Just listened to the track again. Toselli: Serenade Opus 6 ( Maastricht Salon Orchestra). ?? the birds at ear level. Maybe couple of inches above. 

[mansr]

5 minutes ago, STC said:

birds at war level

Probably best not to provoke them.

[STC]

1 minute ago, mansr said:

Probably best not to provoke them.

 

? I hate Iphone auto correct. Meant to say at ear level. 

[mansr]

Another note on stereo recording. In my earlier post, I discussed an XY microphone setup. Consider instead using spaced omnis. Here the difference in distance between the sound source and each of the microphones produces a variation in output level. Additionally, there will be a phase difference with the more distant microphone delayed relative to the nearer one, and this may contribute to our interpretation of the sounds on playback. This still does not, however, help with height or depth localisation. Any points with the same difference in distance to the microphones will give identical outputs aside from overall amplitude. Although the shape of the surfaces formed by such points will be different than for the XY configuration, the effective result is still a total loss of height and depth information. The same is true for any recording method using two microphones.

 

For setups involving more than two microphones, such as the Decca tree, the analysis becomes more involved. However, as long as the microphone pickup patterns are vertically symmetrical, no height information can be encoded.

 

To record the position of a sound source in two dimensions, left/right and up/down, a minimum of three microphones are required. For example, the usual XY or ORTF configurations could be extended with a third microphone pointed more or less upward from the centre. The whole assembly might of course need to be reoriented for best results. A three-channel recording from such a setup would include the height of sounds as well as their left/right location. How to reproduce it is of course another matter, and I have no idea how that might best be achieved. It would, obviously, require more than two speakers.

[semente]

1 hour ago, STC said:

Re: Height in stereo

 

It is my understanding that height is not possible with stereo but in ATD the voice of god indeed sounded as if coming from above with standard 2 channel stereo. 

 

On some occasions, I did perceive height but didn’t bother to find out the reason. Now that I am using a very tall speakers which is almost twice my height from sitting position I do perceive height more often. 

 

OTOH, it is possible that we are using our prior encoded knowledge encoded in is to place height. In one classical recordings, there was some flying birds chirping and I was very sure it sound at hear level before but when I don’t listen but just enjoy the music the chirps appear to be coming from above. 

 

This is purely my observation.  

 

I have a recording of The Hilliard Ensemble made in a Spanish cathedral and in the silent moments one can hear birds chirping. This helps me create a mental image of the space, the tall hard walls, but I can't say that the sound is coming from above. I think or perceived it is because I know how music and sound in cathedral is like and that birds generally hang out out of human reach and close to the windows where there's natural light.

[manisandher]

6 hours ago, Audiophile Neuroscience said:

 

I have been asked that question a number of times before so it's all here on public record.

I have no audio qualifications but have been an audio and music enthusiast my whole life really. In the 90s I probably read every issue of Stereophile and the Absolute Sound. From there I sought out more academic literature and met some extremely knowledgeable and helpful people through connections with audio fora. I am lucky enough to have a fine audio system.

I chose "audiophile" as part of my moniker before I knew it had become a ‘dirty’ word. I don't retract from it. I chose "neuroscience" because I thought it reflected my background interests in the functioning of the nervous system and mind-body relationships. I first did Neurology and then Rehabilitation Medicine morphing into a spine/pain medical specialist. I have formal training in neuropsychology (but no degree) and have also worked in neuropsychiatry. Research methodology and statistics were a necessary part of the training but I have no formal qualifications in that area.

 I have always been fascinated by things perceptual and their physical and psychological influences. Reading as widely as I can in philosophy seems to naturally complement my interests in psyche and soma. Putting together "audiophile + neuroscience" I foolishly thought I could bring some new or different perspective.

I used to put my bio on the CA profile but found some people tended to use the information negatively or to stereotype me. I also used to list my audio system. Then I was recently accused of pretending to have an elitist audio system to pose as an audiophile so I could express anti-audiophile ideas. Go figure!

Cheers

David

 

Thanks David. Neurology, hey? Very interesting.

 

Mani.

[beerandmusic]

height can be "created" in mixing

 

https://theproaudiofiles.com/width-height-depth-in-a-mix/

 

https://www.google.com/search?q=mixing+stereo+to+add+height

[fas42]

8 hours ago, semente said:

 

From what I have read there's no mechanism creating height in stereo images produced by a pair of speakers.

It's probably your brain that expects certain sounds to come from different heights.

 

The LeCleach presentation I posted previously or this:

 

https://theproaudiofiles.com/width-height-depth-in-a-mix/

 

How to Create Width, Height and Depth in a Mix

 

Height

So let’s start with height.

It’s a strange and interesting phenomenon that we hear high pitched frequency content as coming from above, and low tones coming from below.

Partially this is due to suggestion. We subconsciously equivocated “high” pitch with “high on a vertical scale.” Partially, this is due to common tweeter placement with speaker woofers most often being lower than the tweeter in vertical alignment. Partially, this phenomenon is also caused by the way low frequency tones project. The wider dispersion of low tones allows them to reflect off the nearest surface such as your desk. Higher tones are more directional and will reach your ear without as much near reflection over short distances.

For these reasons and probably others, we tend to hear high harmonic content as “up” and low harmonic content as “down.”

By creating contrast in the extremes of the frequency spectrum we can make a mix sound “tall.”

If just one naturally bright element like a bell or hi-hat is a touch brighter, and one low element like a kick or bass is a touch subby-er, the whole mix will expand.

 

I would largely agree with this - I don't particularly 'see' height as being an attribute of the sound, rather space is the character of the presentation I register, a sense of "bigness" to what I'm hearing. As they say , the walls of the listening area disappear, and an arena the size of a football field can be there, or, the concert hall - the information from interaction of sound with the room surfaces is ignored by the brain, and that of the recording acoustic completely dominates.

[fas42]

It's all illusory, but the presentation can be, yes, totally convincing - the difference between being so, and not, is black and white, at least for me - anything less than this level to me is flawed, and I find it easy to discern the actual distortion in the sound which prevents the illusion from forming, when it fails to meet the standard needed.

[sandyk]

4 hours ago, manisandher said:

 

Thanks David. Neurology, hey? Very interesting.

 

Mani.

 

 His hearing isn't too bad either !

It probably helps being trained to accurately interpret what is heard via a Stethoscope as a Medical Professional too. I gather that it is a fine art that has to be learned via experience, possibly a little like learning how to interpret Sonar information buried in noise ?

[Audiophile Neuroscience]

8 hours ago, mansr said:

To record the position of a sound source in two dimensions, left/right and up/down, a minimum of three microphones are required. For example, the usual XY or ORTF configurations could be extended with a third microphone pointed more or less upward from the centre. The whole assembly might of course need to be reoriented for best results. A three-channel recording from such a setup would include the height of sounds as well as their left/right location. How to reproduce it is of course another matter, and I have no idea how that might best be achieved. It would, obviously, require more than two speakers.

 

This is exactly what i was going to ask you about after reading your two previous posts. All makes perfect sense in relation to the limitations of what two microphones in three dimensional space can 'see'.

 

It then obviously begs the question of omnidirectional mics which still basically suffer the same limitations in space despite their wider 'listening' angles. If you like they sample a wider one dimension of three dimensional space - laterality. I get how sources (aka stimuli) moving up and down produce symmetrical reductions in mic output/amplitude, only lateral information is 'seen' differently.

 

The obvious is to add the third mic as you said.Now we have a differential parameter in another dimension which will encode accordingly.

 

Then it struck me, and as you said, we traditionally have only two channels and two playback speakers separated laterally in the one dimension so how to deal with this third dimension being fed from the 3 mic recording?

 

Just some other musings. Representation of depth is easily perceived and presumably due to the change in the mic output/amplitude that we hear as loudness.Things further away sound softer and become louder as the source moves closer to the mic. Lateral information is also preserved allowing to sense if the source is approaching from front to back from the left or right. Additionally, moving from back to front the source sound interacts differently with the room, well at least the mic 'hears' more or less "direct" sound or more or less room reflections at different times. This is easily heard and it seems to me that therefore there is depth information as well as lateral information on a stereo recording. I get that this is NOT a new dimension in the mathematical sense and depth would not excite a differential signal with respect to the stereo mics. Nontheless the physical cues are there for depth similar I imagine to stereoscopic depth perception in vision or hearing.

 

Looking at vision (pun), there is a distinction between "dimension" as in 3D and just distance.There are cues for both. So in the recording mentioned above we are picking up distance (depth) cues. Indeed people can still perceive this type of depth with only one eye (Monocular not Binocular).

 

Regarding sound waves most already know our perception of depth and movement results from various changes in amplitude, frequency, inter-aural differences in arrival time. These things can be manipulated in experiments to create illusions of distance, movement and direction. Clearly not all these parameters can be encoded on to a recording but it appears at least enough cues can be to create a convincing illusion of depth.

 

So the question still remains can the spatial information in recordings, including depth (if accepted cues are there) be measured?

 

The height thing remains a mystery to me. Clearly it can be manipulated into the signal so height is perceived.There is a track on the Moody Blues Search for the Lost chord that sends out a little flying object that circles and orbits above you and around the room. I have heard it irrespective of the room where played. My question again would be can this information built into the signal post recording be measured ?

 

 

 

 

[esldude]

9 hours ago, mansr said:

Another note on stereo recording. In my earlier post, I discussed an XY microphone setup. Consider instead using spaced omnis. Here the difference in distance between the sound source and each of the microphones produces a variation in output level. Additionally, there will be a phase difference with the more distant microphone delayed relative to the nearer one, and this may contribute to our interpretation of the sounds on playback. This still does not, however, help with height or depth localisation. Any points with the same difference in distance to the microphones will give identical outputs aside from overall amplitude. Although the shape of the surfaces formed by such points will be different than for the XY configuration, the effective result is still a total loss of height and depth information. The same is true for any recording method using two microphones.

 

For setups involving more than two microphones, such as the Decca tree, the analysis becomes more involved. However, as long as the microphone pickup patterns are vertically symmetrical, no height information can be encoded.

 

To record the position of a sound source in two dimensions, left/right and up/down, a minimum of three microphones are required. For example, the usual XY or ORTF configurations could be extended with a third microphone pointed more or less upward from the centre. The whole assembly might of course need to be reoriented for best results. A three-channel recording from such a setup would include the height of sounds as well as their left/right location. How to reproduce it is of course another matter, and I have no idea how that might best be achieved. It would, obviously, require more than two speakers.

I don't disagree with what you have posted on this. 

 

However, some X-Y recordings have the microphones positioned to line up the center of the diaphragms and have one positioned a fraction of an inch above the other.  This means that while the directional characteristics are symmetrical there is a distance difference when sounds originate from an upward or downward direction.  When you have differences of distance you'll get comb filtering.  Such could be in the right frequency range to create a sense of height.  It wouldn't be accurate (except by accident), but it seems to me you'll get a notch in the FR in the right area to trigger height perception.  

 

Easy enough to experiment with and see if it happens.  If I weren't occupied with important matters currently I would do it.  May get around to it later if no one else does.  George Graves 

@gmgravesuses a microphone that has the diaphragms aligned vertically in one package, and he reports his recordings display height.  Maybe he could provide a snippet of one that can demonstrate. 

 

You can see below how X-Y and ORTF can have a difference in positioning that is offset vertically.  

 

 

 

 

[Audiophile Neuroscience]

1 hour ago, sandyk said:

 

 His hearing isn't too bad either !

It probably helps being trained to accurately interpret what is heard via a Stethoscope as a Medical Professional too. I gather that it is a fine art that has to be learned via experience, possibly a little like learning how to interpret Sonar information buried in noise ?

 

1 hour ago, sandyk said:

5 hours ago, manisandher said:

 

Thanks David. Neurology, hey? Very interesting.

 

Mani.

 

 His hearing isn't too bad either !

It probably helps being trained to accurately interpret what is heard via a Stethoscope as a Medical Professional too. I gather that it is a fine art that has to be learned via experience, possibly a little like learning how to interpret Sonar information buried in noise ?

 

I have cited the example many times how an experienced cardiologist with reduced hearing acuity can 'hear' subtle heart murmurs better than inexperienced interns with far better hearing acuity. This appears to be true for even the HF components of the murmur where you would swear they would be compromised, certainly in the case of one cardiologist that sometimes struggled with hearing conversations at times. Of course I'd rather have an experienced cardiologist with perfect hearing.

 

A lot is to do with pattern recognition and knowing what to look/listen for.What is uninterruptible noise to one brain is easily perceived and described in detail by another.

 

Mani, yes but I no longer work or would call myself a Neurologist. Whether in neurology or Rehab we worked closely with neuropsychologists. As said I had to pass exams in neuropsychology to get the rehab  med specialist degree. When working in Neuropsychiatry (organic brain syndromes) we had neurologists, a psychiatrist and permanent neuropsychologist on the team. It was revealing to get their different perspectives. To be honest, having read many neuropsychologists reports I found them very skilled, often measurement based, but often telling us what we already knew clinically, NOT always. I find the insights from a good clinical psychologist invaluable in understanding people's behaviour.Now semi retired I do some medicolegal work assessing impairments.

 

The legal dimension introduces a whole different way of thinking and reasoning. Dare I say not so much right or wrong but correct within certain binding parameters (and jurisdictions). Good to have new challenges!

 

[esldude]

This doesn't answer questions related to height, but somewhat does to depth.  

 

Yes, old research from the 1930's.  Still worth reading.  

 

Auditory perspective-Physical Factors by Steinberg and Snow. 

 

http://www.durenberger.com/documents/BSTJLISTFACTORS.pdf

 

Second article in this group published republished by Paul Klipsch in 1964 is the same paper as above though perhaps a little easier to read. 

 

http://www.aes.org/aeshc/docs/bell.labs/auditoryperspective.pdf

[sandyk]

4 minutes ago, esldude said:

Yes, old research from the 1930's.  Still worth reading.

 Yeah.

 So is this old one.

Inside the Vacuum Tube - J. Rider (1945) WW.pdf

[Audiophile Neuroscience]

55 minutes ago, esldude said:

Auditory perspective-Physical Factors by Steinberg and Snow. 

 

http://www.durenberger.com/documents/BSTJLISTFACTORS.pdf

 

A quick read seems to confirm

 

1 hour ago, Audiophile Neuroscience said:

Things further away sound softer and become louder as the source moves closer to the mic. Lateral information is also preserved allowing to sense if the source is approaching from front to back from the left or right. Additionally, moving from back to front the source sound interacts differently with the room, well at least the mic 'hears' more or less "direct" sound or more or less room reflections at different times. This is easily heard and it seems to me that therefore there is depth information as well as lateral information on a stereo recording.

 

The results are better for 3 channel vs 2 but nonetheless, depth is recorded in stereo recordings.Interestingly, the "reverberant" sound is more important for depth than lateral localization but no surprise I guess. Loudness differences as expected are more important in lateral spatial information given the two mics are picking up and producing larger differentials in output/amplitude.

[STC]

1 hour ago, esldude said:

 

This doesn't answer questions related to height, but somewhat does to depth. 

 

 

From award winning recording engineer. 

 

Height

So let’s start with height.

It’s a strange and interesting phenomenon that we hear high pitched frequency content as coming from above, and low tones coming from below.

Partially this is due to suggestion. We subconsciously equivocated “high” pitch with “high on a vertical scale.” Partially, this is due to common tweeter placement with speaker woofers most often being lower than the tweeter in vertical alignment. Partially, this phenomenon is also caused by the way low frequency tones project. The wider dispersion of low tones allows them to reflect off the nearest surface such as your desk. Higher tones are more directional and will reach your ear without as much near reflection over short distances.

For these reasons and probably others, we tend to hear high harmonic content as “up” and low harmonic content as “down.”

By creating contrast in the extremes of the frequency spectrum we can make a mix sound “tall.”

If just one naturally bright element like a bell or hi-hat is a touch brighter, and one low element like a kick or bass is a touch subby-er, the whole mix will expand.

 

 

https://theproaudiofiles.com/width-height-depth-in-a-mix/

[fas42]

2 hours ago, Audiophile Neuroscience said:

So the question still remains can the spatial information in recordings, including depth (if accepted cues are there) be measured?

 

The height thing remains a mystery to me. Clearly it can be manipulated into the signal so height is perceived.There is a track on the Moody Blues Search for the Lost chord that sends out a little flying object that circles and orbits above you and around the room. I have heard it irrespective of the room where played. My question again would be can this information built into the signal post recording be measured ?

 

 

 

 

 

Not quite sure what the point of measuring the spatial information in the recording would be ... there are plenty of recordings with test signals deliberately recorded to make the depth aspect clear cut; and it should be possible to analyse these, and see what's in the waveform. Here, the depth aspect is strongly highlighted; but "normal" recordings would have the same constituents, just less prominent - the principle, for how the playback can reveal such, is similar to shining a light in 'dark' areas; the more powerful the beam, the more detail can be perceived.

 

Manipulated, 'artificial' recordings, say pop albums, have this in spades - the depth "ranking" of various sound elements is quite straightforward to hear.

 

The Moody Blues thing is just playing with phase manipulation between left and right channels, a very overt way of encoding location cues.

[gmgraves]

12 hours ago, mansr said:

Another note on stereo recording. In my earlier post, I discussed an XY microphone setup. Consider instead using spaced omnis. Here the difference in distance between the sound source and each of the microphones produces a variation in output level. Additionally, there will be a phase difference with the more distant microphone delayed relative to the nearer one, and this may contribute to our interpretation of the sounds on playback. This still does not, however, help with height or depth localisation. Any points with the same difference in distance to the microphones will give identical outputs aside from overall amplitude. Although the shape of the surfaces formed by such points will be different than for the XY configuration, the effective result is still a total loss of height and depth information. The same is true for any recording method using two microphones.

I think this is a terrible idea, but a lot of recording and broadcast engineers agree with you. Spaced omnis give a lousy stereo image because they aren't phase coherent. That means, among other things, that you can't mix a recording made with two spaced omnis into mono. Phase cancellations wreck havoc on the resulting mix. Bob Fine of Mercury Living Presence fame found that out early-on. He was making stereo recordings for Mercury before there was a stereo disc to distribute those recordings on. The commercial releases of these early stereo recordings had to be monaural. He quickly found that mixing the the two stereo tracks down to one didn't work. He needed to add a third channel and have his Ampex 300/350 tape recorders modified to three tracks instead of two and he added a third omni microphone in the center. It was from this third center mike track that the mono versions of his Living Presence recordings were cut. When stereo records were finally rolled out in late 1957, he found that the center of the two channel stereo tracks were so confused, image and phase wise, that he started to mix the center channel (originally there only to provide a mono feed)  equally into the left and the right channels. 

[gmgraves]

3 hours ago, esldude said:

I don't disagree with what you have posted on this. 

 

However, some X-Y recordings have the microphones positioned to line up the center of the diaphragms and have one positioned a fraction of an inch above the other.  This means that while the directional characteristics are symmetrical there is a distance difference when sounds originate from an upward or downward direction.  When you have differences of distance you'll get comb filtering.  Such could be in the right frequency range to create a sense of height.  It wouldn't be accurate (except by accident), but it seems to me you'll get a notch in the FR in the right area to trigger height perception.  

 

Easy enough to experiment with and see if it happens.  If I weren't occupied with important matters currently I would do it.  May get around to it later if no one else does.  George Graves 

@gmgravesuses a microphone that has the diaphragms aligned vertically in one package, and he reports his recordings display height.  Maybe he could provide a snippet of one that can demonstrate. 

 

You can see below how X-Y and ORTF can have a difference in positioning that is offset vertically.  

 

 

 

 

Frankly, that amount of vertical displacement is not enough for the microphones to even notice. But what you show above is not an X-Y, pair it's an A-B pair. A true X-Y configuration does not have that vertical displacement. I don't use A-B or Blumlein coincident with separate mikes because there are enough things to worry about when setting-up to do a location stereo recording than worrying about reversed channels (in the above examples, the left-hand mike is point at the right side of the ensemble and vice-versa!). Below, Image #1 is True X-Y and image #2 is Blumlein Coincident.