Well, I can give you my thoughts as I read it, because 30 pages is a bit more than I'm up to in one sitting.
Quote:Ambiophonics is based on almost a century of psychoacoustics research on how the ear/brain localizes sound.
My thought here is of course why would it take 100 years of psychoacoustic research when we're likely going to be discussing the physical properties of sound waves...
Quote:Acoustic Crosstalk. You are listening to a live violinist playing directly in front of you. Both ears hear the violin. The sound at your left ear is similar to but not exactly the same as the sound at your right ear. There are many reasons for the slight sound differences but they are not important now. What is important is that the live violin has produced two versions, two presentations, of the violin sound – one at your left ear and one at your right ear. This is OK because your ear/brain has spent all its life learning to fuse two sound presentations such as this into one image—so what you perceive now is a single, live violin.
Yup.
Quote:Now consider a typical stereo recording of the same violinist. The recording is engineered so that the violinist will appear to be located directly in front of you, halfway between the two speakers. To accomplish this, the two channels of the recording will have similar loudness and will arrive at your ears at about the same time.
Assuming you don't move your head. IF you move your head left, the violinist will appear to also move left whereas in real life, the violinist would appear stationary (which is actually moved to the right relative to your head that moved to the left).
Quote:The problem is that your left ear hears both speakers and your right ear hears both speakers—and the four sound presentations are not exactly alike in level, arrival time, or frequency response. Your ear/brain now has four versions to fuse into a single violin.
No, I think it's better explained by what I just said. The problem with stereo vs. real life, is that stereo only works if the listener is not moving. In real live we move. Anytime there is more than one sound source there MUST and WILL be differences in level, arrival time and frequency response. In the real world, even with a single sound source there will be reflections. Of course I'm picking on the wording of the paper more than anything here.
Quote:Your ear/brain now has four versions to fuse into a single violin. If your left ear heard only the left speaker and your right ear heard only the right speaker, then your ear/brain would be back in the familiar territory in which it must fuse just two presentations into a single image.
Again, assuming that your head doesn't move placing us no more closer to real life.
Quote:The trouble is that your right ear hears the left speaker and your left ear hears the right speaker. This is called acoustic crosstalk, where each ear hears the speaker on the opposite side. Your ear/brain did not evolve to deal with four presentations of the same sound source.
This is not the trouble, it is in fact the solution to making a 3D image from the less than perfect two speaker stereo system. While easy to think a divider from the loudspeakers to your nose to prevent crosstalk would be the answer, this is what we get from a good pair of headphones. Headphone users will tell you that without crosstalk the sound appears to come from inside your head directly between the speakers. To stop this annoying effect in headphones, carefully designed crosstalk is introduced so that at the correct frequencies and amplitude left channel information is introduced into the right ear cup, and visa versa.
Quote:Crosstalk produces incorrect head shadows for center images, reducing the lifelikeness of the image. Head shadow refers to the reduction of mid and high frequencies as sound travels around and over the head to the far ear.
Not sure it actually does unless we stick to the ridged model defined above of a live violinist standing exactly in front of you. A model btw, that is useless in reality because sound is almost never directly square on in front of you.
Quote:When listening to a live instrument directly in front of you, sound travels to the ears with only a small impact from the intervening fleshy part of the face, that is, with only a small head shadow. In contrast, when stereo speakers play similar signals to produce an image directly in front of you—a center image—head shadow is large because sound from a speaker must travel around much of the head to reach the far ear
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Yes, this is what happens in the imperfect stereo playback approach, that fails when the listener moves, but so far no argument that this paper we're reading will solve this problem. Incidentally, Bell Laboratories gave a demonstration of three-channel stereophonic sound on April 27, 1933, with a live transmission of the Philadelphia Orchestra from Philadelphia to Constitution Hall in Washington which if you try the same thing at home AKA mono center channel, the image shifting effect when you move is LARGELY reduced.
Quote:The result for center images is a tonal balance with less mid and high frequency energy reaching the ears than in real life. One can eliminate side-speaker head shadow by eliminating side- speaker crosstalk (difficult) or by moving the speakers close together (easy).
This is certainly true, and supports my average distance between speakers of around 6 feet regardless of room size. And the observation that even closer together than that it is still fully possible to create a listening arc of close to 180 degrees.
It's at this part in the argument that we have to start being specific about the equipment. A simple triode amplifier with no feedback on a good source can make an equally good speaker disappear regardless of where you place it in the listening triangle. However, a mid-fi amplifier on the same speakers will kill the effect - meaning you will hear sound come directly from each speaker cabinet.
Quote:When speakers are close together, side-speaker head shadow cannot occur. Moreover, it is easy to cancel crosstalk when speakers are close together. When this is done, the sonic stage spreads out well beyond the confines of the close speakers—and this wide stage will have lifelike center images
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Easier maybe, but certainly not easy. The crosstalk is actually increased not decreased because the speakers are closer together - placing them also closer to the listener than before. What is changing is the time delay. The delay is shortened, and the ambient reflections from the room are reduced in amplitude compared to the direct sound from the speakers and relative to how loud those reflections were before the speakers were moved closer together.
My gut feeling about reading the rest of the paper is this: If it's based on mathematics then it's likely assumed my comment about a speakers ability to disappear with a Triode Amplifier vs. a typical Solid State amplifier are not considered - making the entire paper void unless applied only to the world of mid-fi. On the other hand curiosity might get the best of me and I'll read it anyway.
For now, I've had my fill.
Thanks,
Steve