[Publius]

Quote:

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.

Quote:

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?

 

[gaboo]

Quote:

Originally Posted by chillysalsa Yes, sound is all oscillations, but to say it's a regular sine wave is an oversimplification. Here's a typical scope plotting a kick-drum beat: The first thing your ear will hear is either a crest, or a tough in the pressure. Any other music will be asymetrical as well. This makes a difference in the way it ends up sounding, and is why one can hear the change due to phase inversion.

Actually, the one that sounded "better"/"more natural" to me had the 1st spike up not down.

 

[gaboo]

Publius, you are right. I was forgetting that sound (pressure) is a longitudinal, not transverse wave. So rudi's argument is false for any sound waves, including sine waves.

Link for the unbelievers.

 

[akira]

Quote:

Originally Posted by rudi 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

?

At 1.5m back, we hear the "impact" in positive signal just 1.5/343 sec later (and weakened a little bit). Positive impluse never change into negative impluse. When you have positive pressure, I may have negative pressure at the same time depending on our position, but the shape of pressure wave we receive are just time-shifted. (pls. exclude effect of the room)

 

[rudi]

Quote:

Originally Posted by Publius 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?

Of course on the scope nothing change, since it start always from the first positive slope ( or negatvie ..depend from trigger polarity ).But following elementary phisics rules, phase is ALWAYS related to distance, this is written in any audio book. This is why in classic stereo the soundstage change with your position related to speakers.
The human hear and brain do not detect instant vectors, but only waves. An increse of air pressure is not detected as sound, but a rotatory variation of pressure ( wave ) is detected as sound. So, if the instant vector do not changhe of 360deg in the defined time, there is no wave and no sound, there is no matter of starting position, only complete rotation is valid. These are elementary rules of acoustics and psicoacustics.
Of course when you change position related to surce ( in the real world )you hear small difference in sound becouse the change in phase interact with reflections in different ways
An example. In silent enviroment sometimes happen to hear a fixed sound ( transformer buzz, far engine etc.. etc..)often is just a matter to move the
head a little bit to don't hear the sound, this becouse the direct waves and the standing waves are in phese opposition and one cancel ( or reduce ) the other. Same way works noise cancellation systems.

 

[gaboo]

Quote:

Originally Posted by rudi Of course on the scope nothing change, since it start always from the first positive slope ( or negatvie ..depend from trigger polarity ).But following elementary phisics rules, phase is ALWAYS related to distance, this is written in any audio book. This is why in classic stereo the soundstage change with your position related to speakers. The human hear and brain do not detect instant vectors, but only waves. An increse of air pressure is not detected as sound, but a rotatory variation of pressure ( wave ) is detected as sound. So, if the instant vector do not changhe of 360deg in the defined time, there is no wave and no sound, there is no matter of starting position, only complete rotation is valid. These are elementary rules of acoustics and psicoacustics. Of course when you change position related to surce ( in the real world )you hear small difference in sound becouse the change in phase interact with reflections in different ways An example. In silent enviroment sometimes happen to hear a fixed sound ( transformer buzz, far engine etc.. etc..)often is just a matter to move the head a little bit to don't hear the sound, this becouse the direct waves and the standing waves are in phese opposition and one cancel ( or reduce ) the other. Same way works noise cancellation systems.

Just quoting you now, I'll reply later...

 

[gaboo]

rudi, how do you explain the Doppler effect? According to you, if you stand still and source of sound is moving towards you, all you should hear are variations in phase...

 

[rudi]

Make the experiment( it is a school lab exercise )
You need a dual channel scope. Connect a microhone on each channell ( A and B) Put the microphones at the same distance from generator speaker and use confortable a test frequency like 5KHz. You will have two waves on the scope screen, similar amplitutde and same phase. Trigger the scope on channel A ( it will be the reference ) and move the microphon connected to channel B. You will see the phase shifting till a complete rotation. This is in perfect accordance with theroy.
About Doppler effect it is based on frequency shift and no to phase shift. Moving to sound source or in the opposite direction will change both, phase and frequency, but the significant value is only the frequency shift.

 

[gaboo]

Sound waves are longitudinal waves. You are ommiting the fact that phase at a given point is also a function of time. More precisely the (unidimensional) equation for a longitudinal wave is: ξ = A cos(ωt - kx). (ignoring the imaginary part).

So with your experiment, you only prove that at some interval λ/2 = π/k (half wavelength) between the mics, the phase is reversed. But, wait, you're talking about a harmonic wave!
Not a transient.

Try this experiment instead: send only one period worth of sound, i.e T = 1/f. you will see the same trace on the scope for both mics, but delayed in time by λ/2c (where c is the speed of sound in air, also know as phase speed). You'll need a scope with memory for this to work.

 

[gaboo]

Look here for difference between longitudinal and transverse waves.

This is how a point source radiates in 2D.

And here for a loudspeaker model.

 

[rudi]

Quote:

Originally Posted by gaboo Look here for difference between longitudinal and transverse waves. This is how a point source radiates in 2D. And here for a loudspeaker model.

Right and interesting but OT related to the basic question. Is phase rotation detectable as a change in sound?
The answer is simple and related to our daily experience. When we move the head of few cm listening music detection of all sound frequncy shift or change phase , but music perception is not changing, therefore we verify that phase shift have no effect on sound in the way that human ear and brain detect sounds.
The only effect is related to the interaction of other enviromental sound.

 

[gaboo]

Quote:

Originally Posted by rudi Right and interesting but OT related to the basic question. Is phase rotation detectable as a change in sound? The answer is simple and related to our daily experience. When we move the head of few cm listening music detection of all sound frequncy shift or change phase , but music perception is not changing, therefore we verify that phase shift have no effect on sound in the way that human ear and brain detect sounds. The only effect is related to the interaction of other enviromental sound.

You can detect reverse phase with just one ear, and just one sound source, without any movement of the head relative to the source.

You are making this issue far more complex that it is. If you really want to discuss binaural hearing and how we use relative phase change to detect "soundstage" start another thread. Btw, a good link on that is http://www.du.edu/~jcalvert/waves/hear.htm.

 

[gaboo]

Quote:

Originally Posted by Publius This is useful. Current psychoacoustic research suggests that hearing is an inherently rectifying operation. Look at the pulse measures about a third of the way down the link: If an impulse is changed from positive to negative amplitude, the electrical pulse response of the ear is delayed by one half "cycle". If the ear really is rectifying the signal then phase/polarity changes have some definite physical basis for being audible, although it's a matter of debate on exactly how audible it really is.

Back to our regualry scheduled program.

Yes, very interesting link. They claim a couple of things: (a) timbre depends on phase. It seem subjectively true to me: one of the samples sounded less like a real drum (I did hear quite a few). (b) we have polarized hearing below a certain frequency. That also seemed subjectively true: the less "real" drum also seemed a bit less impactful.

They've also seen a large variance in people's ability to detect phase. Seems true given what we've seen on this thread.

 

[chillysalsa]

I think everyone is able to hear it, but many are not aware of what to listen for because it is something that is very subtle. Once you are tuned into it, you can detect it more easily than someone who is not aware of the things we have discussed.

 

[Earwax]

Finally got the samples downloaded and abx'ed.

12 of 14 trials right, 0.6% chance I was guessing. I had to bring over the HD600s to get that score, with the HD280s I was only getting a little bit better than 50% right. The difference I was keying on was whether the first drum beat was towards or away from me. A.sonic-whatever was away and B- was towards me. I couldn't even say one was right and the other wrong, just that the direction is different.

I never even realized before that I could tell the difference between "towards" and "away" sounds.