Publius
500+ Head-Fier
- Joined
- Nov 23, 2003
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Well, more like it's not true, period. Pressure signals do not magically rotate phase or invert when they propagate through air... they propagate. Meaning they move through space with very little distortion. When you stand back a meter or so from where you were listening before, in an ideal room, you're going to hear exactly the same thing you heard before, with some attenuation simply because you're further away from the source. This isn't because the ear is phase-ignorant, it's because the pressure waves you are hearing are exactly the same as before, with no phase changes.
Yes, there are frequency dispersion/group delay issues with air, and wall reflections, and off-center imperfections in speaker response, but I don't think they are at all pertinent to this discussion. While in most situations it is true that imperfections in the listening environment (I'd guess primarily reflections and frequency dispersion) are going to distort phase badly, perhaps to where polarity reversal will not matter, that still has no bearing on the notion that polarity reversal is still audible in an arbitrarily good listening environment.
Easy way to test this: pick up your $5 computer microphone, start recording, and snap your fingers 5 inches away. Note the polarity of the first wave of the signal. Now snap your fingers 1 meter away. Did the polarity change in any significant way?
Originally Posted by rudi This is right as principle. But immagine to hear your live drum from a distance of 10 mt and to have the beginning of "impact" as a positive signal at as you said,then move 1.5 mt back, now you ar out of phase of 180deg ( if we assume freq. is 100hz ) and your positive impact is now negative, but drum is still a drum ... which one is the right position to listen?...or better from which position microphones have recorded the sound? If yo listen a live concert from third row or from tenth ( apart of diff sound pressure ) your brain detect the same music even if the phase ar differents. Since there is no a mandatory distance for listening ( and recording ) the phase problem is not a problem since there are no possible solutions. |
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Originally Posted by gaboo That's only true for sine waves. Conside a an ideal (Dirac) impulse: it's phase is unchanged regardless of listening distance. |
Well, more like it's not true, period. Pressure signals do not magically rotate phase or invert when they propagate through air... they propagate. Meaning they move through space with very little distortion. When you stand back a meter or so from where you were listening before, in an ideal room, you're going to hear exactly the same thing you heard before, with some attenuation simply because you're further away from the source. This isn't because the ear is phase-ignorant, it's because the pressure waves you are hearing are exactly the same as before, with no phase changes.
Yes, there are frequency dispersion/group delay issues with air, and wall reflections, and off-center imperfections in speaker response, but I don't think they are at all pertinent to this discussion. While in most situations it is true that imperfections in the listening environment (I'd guess primarily reflections and frequency dispersion) are going to distort phase badly, perhaps to where polarity reversal will not matter, that still has no bearing on the notion that polarity reversal is still audible in an arbitrarily good listening environment.
Easy way to test this: pick up your $5 computer microphone, start recording, and snap your fingers 5 inches away. Note the polarity of the first wave of the signal. Now snap your fingers 1 meter away. Did the polarity change in any significant way?