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Old 17th April 2013, 06:34 AM   #41
jlo is offline jlo  France
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Can I use one sound card as output and another sound card as input with this software?
You need
- two L and R outputs for playing the sweep file
- one mic input for recording

There is only one sweep file with L and then R, to be sure of the real timings between L and R, so to keep true PITD. You may use IR recorded with other softwares but you will never be sure of the timings : generally software automatically align to a certain peak of the IR.
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Old 21st April 2013, 11:06 AM   #42
jlo is offline jlo  France
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I am curious though, how would one distinguish between a phase problem vs amplitude problem?
I have now separated views of PITD and PILD, so you can see both effects.

IE here I moved the mic only 10cm to the left, you see that amplitude has minimal changes but time (PITD) moves quite a lot the phantom image to the left.
Blue is the amplitude, red is time and green is combination of both.
Click the image to open in full size.
I think you really need very high directivity speakers to keep the image central ! and frequency stable
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Last edited by jlo; 21st April 2013 at 11:15 AM.
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Old 21st April 2013, 01:43 PM   #43
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Clearly bias exists in your setup for high directivity speakers. Your bias is based on previous experiences with toe-in for your speakers.

Rest of experiment is crude reproduction of HRTF data collection. Image location in recordings is well defined as head tracking setups with HRTF corrections demonstrate.

Fuzziness in image is all about the speakers ability to act as single source in space and time. First approximation demonstrating this is tendency of smaller speakers producing more image detail than larger speakers. Smaller speaker inherently has smaller footprint in space and time than larger speaker. For same speaker locations and listener location smaller speaker subtends smaller angle.

When listening triangle is expanded so that larger speaker subtends same angle at listening position as smaller speaker with smaller listening triangle imaging detail of two systems becomes more consistent. However, bigger speaker with bigger listening triangle implies bigger listening space.

Much better approach is assessing angular separation of two elements within a phantom image is at what point of angular separation do two vocalists sound like they are coming from two locations instead of one? This becomes blur factor of speaker system. Instead of two vocalists, various signals may be substituted, and synthesis of locations may be investigated as to panning techniques used to place virtual sources into phantom image. All results come from perceptual domain of listeners, and leads to credible results.

A variation of approach: Instead of just two speakers, each is represented as pair of miniature monitors placed side by side. Starting with arrayed monitors touching, the pair of arrays are set up in listening triangle, and may subjectively be toed in/out to get perceived best image in conjunction with optimizing triangle size and location in listening space. From such a baseline the arrays are modified by introducing spacing in arrayed speakers and listening results obtained.

What we hear listening to speaker is convolution of signal with space/time signature of speaker.
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Old 23rd April 2013, 03:07 PM   #44
soongsc is offline soongsc  Taiwan
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Originally Posted by jlo View Post
I have now separated views of PITD and PILD, so you can see both effects.

IE here I moved the mic only 10cm to the left, you see that amplitude has minimal changes but time (PITD) moves quite a lot the phantom image to the left.
Blue is the amplitude, red is time and green is combination of both.
Click the image to open in full size.
I think you really need very high directivity speakers to keep the image central ! and frequency stable
This seems consistent with toe in findings of many. If the speakers are toed in the right way, it seems that imaging and depth improve. But I also find that some people do not prefer this.
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Old 24th April 2013, 04:54 PM   #45
Pano is offline Pano  United States
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I had a strange phantom image experience yesterday. I was listening to Firesign Theater's Everything You Know Is Wrong on vinyl. In the part where Nino the Mind Boggler moves from the telephone to the TV, his voice was very precisely 2 feet to the right of my right speaker. Solid.

When Nino was in the telephone on the left his voice was pegged to the left speaker, as I might expect because it's panned hard left. But over on the right - 2 feet past the speaker, as clear and solid as you could want. Weird..... (They don't call him the Mind Boggler for nothing).

I do sometimes hear music that extends past the speakers, but it's nebulous. To hear a voice pegged precisely 2 feet past the speaker was freaky.
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Old 24th April 2013, 05:46 PM   #46
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Hi Pano

Well that is interesting umm, we have been to the old same place.

Did you notice that when Nino moved to the Tee&Vee that you also heard the old time flyback transformer ring up high?
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Old 24th April 2013, 09:37 PM   #47
Pano is offline Pano  United States
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Ha! No Tom, I didn't. But my hearing up that high is gone. 15.75KHz is a distant memory. I wouldn't hear a flyback now if it bit me in the ear. I'll listen again.
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Old 24th April 2013, 10:45 PM   #48
DDF is offline DDF  Canada
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Originally Posted by jlo View Post
Here comes my question : how can we objectively measure subjective localisation ?
Hi jlo, here are some previous experiments with subjective experiments:
In rooms:
http://www.pa.msu.edu/acoustics/rooms1.pdf
https://secure.aes.org/forum/pubs/journal/?elib=6050

In anechoic chamber:
AES E-Library Horizontal Plane Localization Ability and Response Time as a Function of Signal Bandwidth

Here was an attempt at purely objectively essessing localization with a "virtual listener":
AES E-Library Objective Assessment of Phantom Images in a 3-Dimensional Sound Field Using a Virtual Listener

Dave
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Old 22nd June 2013, 03:18 PM   #49
Pano is offline Pano  United States
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Originally Posted by gedlee View Post
Some years ago I used a bowling ball to get decent data for head diffraction. It was actually reasonably close to the real data, but with a bowling ball the results could also be compared to numerical models. Used bowling balls are dirt cheap, almost free. Any object in the middle of the two IRs would be better than nothing.
I've been wanting to do some measurements similar to this and figured the bowling ball to be a great idea. Or maybe a soccer ball. But then I got to looking at the dimensions and saw that the diameter of a bowling ball or #5 football (soccer) is larger than the typical distance between the ears by at least 50%. More for the soccer ball.

How much would this matter?
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Old 22nd June 2013, 03:28 PM   #50
gedlee is offline gedlee  United States
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Pano

It would matter some, but options are quite limited unless you get an actual dummy head. They are available for hearing research and not too expensive. I recently used one for Lidia, placing mics in the ears.
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