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Old 7th April 2013, 08:01 PM   #11
Pano is offline Pano  United States
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Quote:
Originally Posted by jlo View Post
...does the phantom image stay more central than with low directivity speakers ?
My experience says "No". But that's in large spaces where I've heard omnis do a very solid central image. Will be interesting to test wide vs narrow vs room size.
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Old 7th April 2013, 09:53 PM   #12
breez is offline breez  Finland
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Hi jlo,

You may find useful techniques for localization estimates in the doctor's thesis "Binaural localization and separation techniques" by Harald Viste. It is available for download Binaural localization and separation techniques

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.

Relevance to phantom source localization? Hard to say, but worth a try at least? The above operates with binaural signals, of course, necessitating some sort of model head or mics in your ears. The signals are analyzed by a simplified head model, ie. you don't need real HRTF data for useful results.
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Old 8th April 2013, 01:20 PM   #13
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Quote:
Originally Posted by markus76 View Post
When the barrier was removed, spatial quality didn't degrade. But when I listened the next day, starting without the barrier, spatial quality was clearly degraded. It seems the brain holds on to a certain "processing" for some time.
I find this to be the case when I listen to music with headphones right after a TV show or movie on my projector. The sound sticks to the screen.

I would to exploit more visual clues in a stereo setup. They make such a crazy big difference. Just the appearance of a center speaker helps to center the phantom image for me.
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Old 8th April 2013, 02:32 PM   #14
dewardh is offline dewardh  United States
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Originally Posted by SEdwards View Post
The sound sticks to the screen . . . I would to exploit more visual clues in a stereo setup
I think that's nine tenths of the reason we hear reports of "better" imaging with multi-channel HT systems . . .
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Old 8th April 2013, 04:01 PM   #15
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to measure the localization, consider the simple..

one speaker in each corner of the room with the microphone in the middle (time delay to offset the microphone too).

turn one speaker off and then half of the room can fill up with decay in front of the microphone

turn both speakers on and the decay in front of the microphone would go down.
if it doesn't then your window (or gate?) isn't shallow enough and the decay from behind the microphone is coming back up front to be recorded by the microphone.

you'd also be able to note a stronger amplitude in frequencies, especially the summed frequencies between the two speakers where normally dips and peaks would occur.
within that context, the size of the room will equate the peaks and dips .. but the thing to note is the rise in amplitude when no equalizer adjustment has been made, in comparison to a volume increase across the entire frequency band.
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Old 8th April 2013, 04:03 PM   #16
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quite the gamble without adjustable window and|or gate, as well as the concept of the room itself interacting with the recorded measurement when things are shallow enough to pick up only what is in front of the microphone.
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Old 8th April 2013, 04:05 PM   #17
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Originally Posted by dewardh View Post
I think that's nine tenths of the reason we hear reports of "better" imaging with multi-channel HT systems . . .
I don't think this is it. I think the fact that you rely less on phantom imaging is the key. A actual speaker outputting information is much better than a phantom image. It is certainly much more stable that is for sure.
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Old 8th April 2013, 05:13 PM   #18
Elias is offline Elias  Finland
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I think this is highly interesting subject ! A few years back I did something very similar, with Octave too


Quote:
Originally Posted by jlo View Post
an indicator to compare localisation from various loudspeakers in rooms.
This was also my goal, but I concentrated on ITD. I tried to see through analysis how speaker directivity affects in ITD in a small room.





Quote:
Originally Posted by jlo View Post
A few remaining questions :
- can we really avoid measuring with an artificial head and simply work with L and R impulse responses ?
- should we use a frequency dependant time widow ? a longer window ?
- does the calculated IACC represent the real ITD over the whole spectrum ?
- is IACC + level enough or are there other parameters to add such as HF signal enveloppe, HRTF, binaural crosstalk,... ?
- what frequency filtering should be used : gammatone, 1/6 octave,...
- how should ITD be calculated ? IACC, direct phase, groupdelay, envelope of signal ?
- time/angle and level/angle are now linearly approximated : should this be changed ?
- should we measure over a whole listening area to check stability of localisation ?
- should we also measure with non central phantom sources ?
- and the most important, does this analysis correlate to perception ? how to precisely check it ?

Plenty of good points there. You really have given a thought on these matters

Here's some my thoughts:

-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.


As said it was few years ago since my last analysis. I had great plans but was limited in available time


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Old 8th April 2013, 07:28 PM   #19
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Hi
Just a thought;
As there can be a considerable difference between two differently designed pairs of loudspeakers in their ability to produce a mono phantom image and also suppress the R and L origins (even outside of the rooms effects), it might be useful to first use a single source in your rooms center and measure to see what a real mono source looks like (using your metric).

Also, our hearing sensitivity curve is a pretty large clue as to where our acuity is as well, so a small full range driver and voice range test signals may be worth trying in addition wideband.

Fwiw, Pat Brown (Synaudcon) uses B-format microphones to derive multichannel room impulse responses and has written some on the topic of capturing stereo in general, this on accuracy or realism.

Accuracy vs Realism Synergetic Audio Concepts

These may be of general interest too.

http://www.mmad.info/Collected%20Pap...20pages%29.PDF

http://www.2010.simpar.org/ws/sites/DSR2010/09-DSR.pdf

Best,
Tom
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Old 8th April 2013, 07:38 PM   #20
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Quote:
Originally Posted by Tom Danley View Post
there can be a considerable difference between two differently designed pairs of loudspeakers in their ability to produce a mono phantom image and also suppress the R and L origins
Hi Tom,

Has that effect ever been investigated?
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