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Old 17th February 2010, 01:35 PM   #421
keyser is offline keyser  Netherlands
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Originally Posted by gedlee View Post
There is also a time factor involved. The longer the signal is on the better you can resolve its location. A short LF wavelet would not be localizable in any environment.
In a room I'd think it to be the other way around: the low-passed speech fragments Markus posted probably change in frequency too quickly as to not fully activate room-modes. On steady sine-waves I can't hear the direction up to a couple hundred hertz.
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Old 17th February 2010, 01:43 PM   #422
gedlee is offline gedlee  United States
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What would constitute a "wavelet"? Less than a full cycle at that frequency?
Would that difficulty also apply to wavelets of a higher frequency?
It would take several cycles of the sound for the ear to resolve anything from it. The ear does not have a sampling system and it can't react instantaneously, so the signal has to be somewhat stationary for several cycles to be resolved in the brain. For a 100 Hz this would be about 50 ms. - well into the reverb tail of any small room.
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Old 17th February 2010, 01:48 PM   #423
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It would take several cycles of the sound for the ear to resolve anything from it. The ear does not have a sampling system and it can't react instantaneously, so the signal has to be somewhat stationary for several cycles to be resolved in the brain. For a 100 Hz this would be about 50 ms. - well into the reverb tail of any small room.
Please excuse my ignorance on the subject, but does this mean that less than about 5 periods of a 100 hz tone would not be heard at all?
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Old 17th February 2010, 02:07 PM   #424
gedlee is offline gedlee  United States
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Please excuse my ignorance on the subject, but does this mean that less than about 5 periods of a 100 hz tone would not be heard at all?
Your ability to detect its pitch, or its direction would be seriously degraded. You would "sense" something, but you could not really tell what frequency it was. Hence, in a small room the sound field has reached steady state well before this happens, which is the reason that I state that the sound field in a small room at LFs is basically a steady state situation and as such the EQ should be done on the steady state signals. To be valid this requires spatial and frequency averaging. This is quite different than the situation above say 500 Hz where we can resolve pitch and direction of even the direct signal well before there are any reflections - unless those reflections are coming very soon. If they do arrive very soon after the direct sound then the ear will use them in its analysis.
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Old 17th February 2010, 03:49 PM   #425
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Let me start by stating that I haven't really investigated the theory of the matter of localization of low-frequency sound-sources. Two of my observations however contradict with what you are saying (EDIT: not necessarily in the above post).

With a sine-wave it is impossible for me to hear the direction from which it originates up to a couple of hundred hertz. This is in line with what you are saying. But how do you explain that hearing direction on those low-passed speech samples Markus posted is so easy?

You say we mainly hear direction on the basis of level differences and differences in time of arrival at both ears, and that these differences are too small to be able to hear direction of low frequencies. This seems intuitively right to me. Yet I can easily hear direction of low frequency sine-waves outside, without early reflections except from the floor. How is this possible?
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Old 17th February 2010, 04:05 PM   #426
gedlee is offline gedlee  United States
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Let me start by stating that I haven't really investigated the theory of the matter of localization of low-frequency sound-sources. Two of my observations however contradict with what you are saying (EDIT: not necessarily in the above post).

With a sine-wave it is impossible for me to hear the direction from which it originates up to a couple of hundred hertz. This is in line with what you are saying. But how do you explain that hearing direction on those low-passed speech samples Markus posted is so easy?

You say we mainly hear direction on the basis of level differences and differences in time of arrival at both ears, and that these differences are too small to be able to hear direction of low frequencies. This seems intuitively right to me. Yet I can easily hear direction of low frequency sine-waves outside, without early reflections except from the floor. How is this possible?
I have not listened to Markus demos so I can't comment. I suspecxt that there is some significant information well above 100 Hz.

Theoretically you should not be able to localize 50 Hz out of doors. I can't explain your results execpt to say that any nonlinearity will defeat the test because you can easily localize on the harmonics.

I usually do not worry about distortion from a sub for several reasons, but the harmonics CAN make the sub localizable and that is a problem.
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Old 17th February 2010, 04:10 PM   #427
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I thought of the possibility of harmonics causing the ability to localize the source, but with a stimulus of 100 hz that would have to mean quite an amount of higher order harmonics. Not impossible, but unlikely IMHO.
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Old 17th February 2010, 04:26 PM   #428
Jmmlc is offline Jmmlc  France
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Please excuse my ignorance on the subject, but does this mean that less than about 5 periods of a 100 hz tone would not be heard at all?

Hello,

5 periods of a a 100Hz pure tone (sine) will possess a complex spectrum (a lot of components with f < 100Hz and also some over 100Hz). It will most surely not sound as a pure tone...

Give a look to the spectrum of a pulse made of 5 periods of 100Hz sine in the attached file. (the 5 periods are preceded and follown by 10seconds of silence.)

Best regards from Paris, France

Jean-Michel Le Cléac'h, France
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File Type: jpg 5period_100Hz.jpg (79.5 KB, 123 views)

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Old 17th February 2010, 04:37 PM   #429
gedlee is offline gedlee  United States
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Originally Posted by Jmmlc View Post
Hello,

5 periods of a a 100Hz pure tone (sine) will possess a complex spectrum (a lot of components with f < 100Hz and also some over 100Hz). It will most surely not sound as a pure tone...

Give a look to the spectrum of a pulse made of 5 periods of 100Hz sine in the attached file. (the 5 periods are preceded and follown by 10seconds of silence.)

Best regards from Paris, France

Jean-Michel Le Cléac'h, France
Jean-Michel

No one would do it that way!! And in all my discussions I said a "wavelet" meaning a slow rise and fall of the wave. This would have a very narrow range of frequencies centered on 100 Hz. But of course you knew that, which makes me wonder why you made such a comment.
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Old 17th February 2010, 04:39 PM   #430
gedlee is offline gedlee  United States
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I thought of the possibility of harmonics causing the ability to localize the source, but with a stimulus of 100 hz that would have to mean quite an amount of higher order harmonics. Not impossible, but unlikely IMHO.
How much harmonic content is required? The third harmonic at 300 Hz could be quite detectable (as far as localization is concerned) at even very low % THD.
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