sibeen said:
mollwollfumble said:
> A microphone connected to an amp connected to an oscilloscope can do a reasonable facsimile.
That’s a single pixel. I want to see sound in at least 1028*768 pixels.
What? A sound is a frequency, or multiple of frequencies if you prefer, that varies in amplitude in the time domain. That’s exactly what an oscilloscope represents. It’s as if it’s made for examining something like this.
Thank you for giving me an opportunity to explain.
A sound is a pressure wave. In air the sound wave has time dependence, frequency, and direction. In exactly the same way, light is a wave that has time dependence, frequency and direction. Every non-quantum thing we can physically do with light, we can do with sound and visa versa. In physical theory. We even refer to “phonons” as the acoustic quantum equivalent of “photons”.
It’s the direction of sound that I’m talking about. Light approaches us from millions of directions at once. In exactly the same way, sound approaches us from millions of directions at once. So we can plot the sources of approaching light and call it a photograph.
Similarly, physics tells us that we can plot the sources of approaching sound to make something exactly analogous to a photograph.
But we don’t. Our biology and psychology stops us from thinking about sound in this way. It’s a limitation of being only human that we haven’t yet come to grips with. Because we have two ears we are fooled into thinking that stereo reproduces the directionality of sound, it doesn’t. Because we can move our head, we think that although stereo doesn’t suffice, 5.1 or 7.1 surround sound does. It doesn’t. 7.1 surround sound is only the equivalent of a photograph with just 8 pixels.
Which leads me to wonder if there’s a way to overcome this biological and psychological barrier with tools. It’s hard for me to think about and I’m far from sure that I’ve got the answer correct.
One starting point could be a three-axis accelerometer producing a signal at least 40,0000 times a second. Computers can operate at 900 MHz and above, so that’s no problem. Sound is a directional pressure wave so induces a directional vibration in the accelerometer. A three-axis accelerometer can exactly pinpoint the directionality of a single sound source. But it gets fooled if there are two sound sources of the same frequency.
With a second three-axis accelerometer, a measurement of the phase difference between the two accelerometers helps to separate out two independent sound sources.
This is the point at which being “only human” fails me. For arbitrarily many sound sources, how many three-axis accelerometers would be needed, and what software would be needed? I haven’t a clue. Perhaps only four arranged in a tetrahedron, perhaps as many as the number of independent sound sources, perhaps even that isn’t enough.
Perhaps there’s a way of focussing sound, not like the lens of a camera, too much dispersion and diffraction, but like the grazing incidence reflectors of an X-ray telescope. Focussing not to get a single point but to get an image, imposed onto a sheet of microscopic accelerometers (or equivalent size microphones).
Or perhaps a rigid sphere is enough, studded with a million or more microphones each pointed in a different direction, using the sound shadow to aid directionality. Or would that be fooled by 7.1 surround sound?
If the “only human” aspect of pixels of sound gives me cognitive trouble, what about pixels of smell?
¿Huh? you may think, smell isn’t a wave. It isn’t … but …
Smell is a gradient, and a gradient always has a unique three-dimensional directionality. So there’s nothing in physics to stop me from building a tool detecting the smell concentration gradient accurately enough to make a picture of the direction that smell is coming from. In this case though, multiple sources of the same smell could probably not be separated out, a single direction for a single molecule. The direction would jitter around as a function of the local air speed.
Our “only human” limitations of smelling and hearing ability stop most of us from thinking about these.
