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Old 8th April 2013, 08:21 PM   #21
graaf is offline graaf  Poland
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interesting
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Old 9th April 2013, 07:07 PM   #22
jlo is offline jlo  France
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Originally Posted by jlo
...does the phantom image stay more central than with low directivity speakers ?
My failure... I wanted to say high directivity speakers !
I already did some measurements comparing toe-in and straight position : the speakers crossed in front of listening place show better phantom image stability

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Originally Posted by breez View Post
You may find useful techniques for localization estimates in the doctor's thesis "Binaural localization and separation techniques" by Harald Viste
One main finding is that better estimates are available by considering the ITD and ILD jointly in each frequency band. Angle estimates from ILD tend to be noisy while estimates from ITD have ambiguity above 1.5 KHz. The noisy ILD estimates can be then used to select the right angle estimate from ITD..
I already use both ITD and ILD for the calculation. Contrary to the thesis, I have no problems with noise, I don't want to find real sound positions : I want to estimate phantom image. So I can work with generated signals (sweeps, aso).

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Originally Posted by Elias View Post
-If you plan to analyse ILD you really should have a head diffraction model.

-I used a wavelet transform so time windowing was not an issue but rather a built in feature. My focus was to include room reflections to see their effect on ITD, not to filter them out.

-The wavelet was matched to model cochlear frequency filtering. I used ERB to define bandwidth. Gammatones are fine too, I've used them occasionally as well.

-I calculated ITD from the phases of the interaural wavelet transform. It's straigth forward and very simple.
Interesting that you also did something similar.
I analyse ITD but as it is a comparison between setups, I don't need to get exact values so no need to add a head diffraction model, I think.

I tried wavelet transform but it didn't get good pictures !
For the bandwidth, I will make trials with ERB : but the difficult part will be correlation between measurements and listening.
For the ITD, I use IACC, it is also easy to calculate and seems to give stable results.

Another question :
the estimated source is at the mean position given by ITD and ILD estimations. It works when ITD and ILD are opposed : this is the well known time-intensity trading. This also works when ITD and ILD give identical direction cues (the natural way).
So in the software, I supposed that the estimation would work in-between....
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Last edited by jlo; 9th April 2013 at 07:14 PM.
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Old 11th April 2013, 08:14 AM   #23
soongsc is offline soongsc  Taiwan
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It seems like an interesting project. Are you trying to use an existing known recording to generate a signal, and then measure and calculate whether the source image is located at the same angle of the original recording?
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Old 11th April 2013, 08:53 AM   #24
jlo is offline jlo  France
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Are you trying to use an existing known recording to generate a signal, and then measure and calculate whether the source image is located at the same angle of the original recording?
Not at all. To do this you would need a dummy head. And probably also use other parameters such as HRTF.
My purpose is easier : I record separately impulse records of left and right speakers. From those IR, I can calculate ITD (from IACC) and ILD for each frequency band. Combining both gives me frequency dependant localization of a theorical phantom central source. Idealy, this source should be central over all frequencies. This is not the case in real measurements due to asymetrical speaker responses, position and room.
Interestingly, you can see the effect of a non central listening position : the phantom may collapse more or less quickly to the nearest speakers, this depends on factors such as loudspeakers directivity. Ie, you may measure if low or high directivity is better for spatial reproduction
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Old 11th April 2013, 09:37 AM   #25
Elias is offline Elias  Finland
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How do you have ILD if no head shadow ? For a transparent head model both ear signals are the same.
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Old 11th April 2013, 09:46 AM   #26
soongsc is offline soongsc  Taiwan
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I see, this is more a tool to help determine optimum location arrangement in the room.
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Old 11th April 2013, 10:52 AM   #27
jlo is offline jlo  France
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this is more a tool to help determine optimum location arrangement in the room.
yes another possibility

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For a transparent head model both ear signals are the same.

I don't measure influence of the head. I measure ITD and ILD due to loudspeakers and placement in room. An ideal setup, perfect speakers in an anechoic room, would give a perfectly central phantom image at all frequencies.
The independant measurements for L and R would allow to use a head model to estimate ITD and ILD as if there was a head, but I'm not sure that it would bring something.
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Old 11th April 2013, 03:52 PM   #28
gedlee is offline gedlee  United States
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This is what the software on my web site was designed to do, but the model of image location was very simple. It would be interesting to compare my results with yours. We both found that the center image was stabilized by crossing the speakers in front of the listener. Are you using real speaker polars? I'm not clear on the model input.
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Old 12th April 2013, 10:03 PM   #29
jlo is offline jlo  France
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Originally Posted by gedlee View Post
Are you using real speaker polars?
No, I use no model for the speakers, I use real measurements of IR.
I'd also like to compare both software and localisation model.
For my soft to compare stability of phantom image, I need to get :
- IR of left speaker and IR of right speaker at 0 for speakers facing listener
- same with some lateral move (30 or 50cm ?)
- same central position but with toe-in
- same toe-in and lateral move
but you can also download the soft (it's free here : http://www.ohl.to/audio/downloads/pops.zip) and try for yourself. The only tricky part is that Octave has to be installed, see setup page of Pops.
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Old 15th April 2013, 03:39 PM   #30
gedlee is offline gedlee  United States
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Sorry for delayed response - busy again. So you measure the impulse response at two point in the room separated by the distance between the ears? Then you use a calculation to find the IACC from which you get the ITD and the ILD? You use these to determine the image location? Is this all correct?

I would have to agree with a comment made earlier, that this approach is based on HRTF results and as such must have a head in place to get meaningful data. When I did my image software I used results posted by Blauert which were made as a composite that already had the head diffraction data included.

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.
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