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General Asylum General audio topics that don't fit into specific categories. |
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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Thanks, but aren't we talking about two different things? posted by David Spear on August 7, 1999 at 19:23:41:
Hi Dave,I've just been repramanded for making such long posts, but here goes another one. Thanks for letting me know that you're not bothered too much by my long winded nature.
It's pretty clear by now (if you've followed all of this thread) that the Doppler distortion Dr. Kimber is addressing is quite different from the more common use of the term, so we are clearly talking about at LEAST two different things.
Your opening paragraph is interesting to me because like other posts made in this thread it sits very close to the source of all the confusion over "Doppler distortion." You start with a perfect explination of the classical understanding of Doppler effect, but then the water muddies. You asert that:
"once the sound waves are in the air, no further modulation takes place. (The low-frequency waves moving through the air cannot "push" the high-frequency waves, they simply interpenetrate each other.) Of course, superimposition of waveforms occurs, but the low-frequency waveforms do not cause the superimposed high-frequency waveforms to change in pitch."That's mostly right. But forget Doppler shift for a moment, and let's talk about the air. Here's this high frequency wave sitting in this air, and suddenly the air molicules that contain the wave are compressed. At the micro level the molicules all get the same compression, but at the macro level, everthing in the air, including the high frequency wave, gets squeezed into a smaller space. The wave length of the high frequency wave is reduced and it's pitch is increased, when it is squeezed into a smaller space. If the air is stretched to occupy a larger space, the waves in that air get stretched too, and their pitch is decreased. This very thing happens whenever sounds from different sources mix, longer wavelengths compressing and expanding shorter waves that are within their "area of control" so-to-speak. This is NOT Doppler shift in the way we normally think about it, but note the similarities. The low frequency waves modulate the high frequency waves slightly, just as if they were pushing them around. In fact, they are pushing them around, only by squeezing and stretching them. Perhaps this is another manifestation of the Doppler shift. It does appear to be what Dr. Kimble is talking about. By separating the sound into components based on frequency and then letting them recombine in the atmosphere we inadvertantly introduce additional frequency shifting of the higher frequencies when the sounds re-combine. Such shifts existed in the original, but our speaker has now caused it's own set of shifts, and I think this is the distortion Dr. Kimber is trying to remove for us. I hope he methods really work, but I think his use of the term "Doppler distortion" to describe the effect is creating a lot of confusion.
Hopefully we'll all know soon how much of this I've got right and how much of it I've got wrong.
So much for Doppler. Now on to the rest of your post.
Your comments about "controlling a complex pattern of waveforms" are well taken, but as I pointed out somewhere else on the forum, the speakers don't really control the waveforms in the room at all. They only excite them, which is quite different.
Your five step approach is pretty sound, though we might disagree on a few minor details. In a way it's an almost ironic over simplification. Ah but were the world only so simple. :-)
Your comment about "the best that can be hoped for in a home audio system" is one that I would be hesitant to make. Not just becasue one's hopes should always exceed ones grasp, but because the best that is absolutely possible is probably WAY beyond anything any of us has ever (or ever will) experience.
It seems that we mostly sit in agreement. Reused terms have confused us, as they are so prone to do, but the music still sounds great.
Be excellent,
Charles
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Follow Ups
- This is an interesting side trip. - Charles 21:27:23 08/07/99 (3)
- Opening another can of worms... - David Spear 00:27:24 08/08/99 (2)
- OH NO! More worms! - Charles 01:59:31 08/08/99 (1)
- I think we agree on the worms ;-) (nt) - David Spear 03:26:54 08/08/99 (0)
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