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Old 24th July 2009, 10:30 PM   #91
gedlee is offline gedlee  United States
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Quote:
Originally posted by catapult

Computer speakers don't really count as a 'bad' system because you're listening in the nearfield where the sorts of room effects being tested are minimal.
This is a good point, I will do the test again.

I am not saying that this type of signal is meaningless at revealing some aspects of the problem, it's the interpretation of the results, as given here, that I have a problem with. I do almost nothing subjective, except listen to music. I am most interested in objective means for quantifying our perceptions. These signals may have some usefulness in that regard, but maybe not. Noe the less, the justification for their use in objective assesment is not there at the present, from what I can see.
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Old 24th July 2009, 11:01 PM   #92
KSTR is offline KSTR  Germany
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I only partly agree. The problem is IMO that these kinds of narrowband signals have so many parameters that it is not very easy to find the best possible suited signal structure that could be assessed both manually and could be analized by some form of post processing giving results consistent with actual perception, along the lines (but not restricted to) the idea that Elias has presented. "Best possible" to be read as giving the most stable results under varying circumstances. I pretty much appreciate his work and see it as a starting point for further studies. After all the goal is to minimize or flatten out all modal effects as much as possible, with all means we have. Those test signals are also very nice to find the best places for absorbers etc. I personally used them even for recording situations to find mic and source positions that don't suffer from modal problems.

I found that with my signals it is interesting to listen what happens to the perception with or without any background noise. There is a big difference between complete silence (at night, using a cdplayer) and some broadband background noise like PC fan/hdd noise etc. With background noise the sensitivity to the modal phenomena is better as one can listen to how the noise gets masked in different ways depending to what is happening in the gaps between the bursts. In fact I have CD versions with extra noise added in for loactions/setups where it is too quiet.

- Klaus
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Old 24th July 2009, 11:01 PM   #93
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Quote:
Originally posted by gedlee


This is a good point, I will do the test again.

I am not saying that this type of signal is meaningless at revealing some aspects of the problem, it's the interpretation of the results, as given here, that I have a problem with. I do almost nothing subjective, except listen to music. I am most interested in objective means for quantifying our perceptions. These signals may have some usefulness in that regard, but maybe not. Noe the less, the justification for their use in objective assesment is not there at the present, from what I can see.
Earl, the thing is none of your systems may have a problem at 100Hz so, of course, the test won't show any problems. SL's graphs show pretty clearly what happens with a bad frequency in a bad speaker/room combo. I think those graphs are from his original AES paper on the testing method. Elias is just building on his work, plotting energy/time curves (time being expressed in periods) of all the frequencies on one graph.
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Old 24th July 2009, 11:12 PM   #94
KSTR is offline KSTR  Germany
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Linkt to Linkwitz page on this AES paper:
http://www.linkwitzlab.com/AES%2798/aes-98.htm
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Old 24th July 2009, 11:28 PM   #95
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The original testing-method paper is this one from 1980.

Siegfried Linkwitz, Shaped Tone-Burst Testing, JAES, Vol. 28, No. 4, April 1980

Abstract:
http://www.linkwitzlab.com/publicati...urst%20Testing
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Old 24th July 2009, 11:44 PM   #96
gedlee is offline gedlee  United States
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Quote:
Originally posted by KSTR
After all the goal is to minimize or flatten out all modal effects as much as possible, with all means we have.

- Klaus
I agree, what does the time domain have to do with that? Basically, if the LF response is as smooth as possible it will likely have the lowest decay rate as well (although that requires Minimum phase to be absolutely true and you can't prove that the LF stuff is MP). Discussing how any one type of source acts in time does nothing towards the goal of a smooth LF response.
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Old 26th July 2009, 12:02 AM   #97
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Quote:
Originally posted by gedlee


I agree, what does the time domain have to do with that? Basically, if the LF response is as smooth as possible it will likely have the lowest decay rate as well (although that requires Minimum phase to be absolutely true and you can't prove that the LF stuff is MP). Discussing how any one type of source acts in time does nothing towards the goal of a smooth LF response.
Actually, as we discussed before Earl, in a typical room the source to listener transfer function is typically not minimum phase. The result is that tests such as those presented here do not correlate to amplitude response at all. It is not even clear that the smoothest amplitude response would necessarily yield the "best" transient, what ever that is?
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Old 26th July 2009, 01:32 PM   #98
KSTR is offline KSTR  Germany
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IME the very lowest order modes (say fundamental and second) are pretty close to MP. Then my goal is to setup the speakers and listening pos so as to have only boosts, not notches at those freqs and then apply reverse (MP) notch filters. The higher order stuff which is clearly not MP must be dealt with by room treatment and, again, optimized placement. Finally some gentle (broadband) overall EQ to get the amplitude response right.

- Klaus
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Old 26th July 2009, 05:16 PM   #99
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Quote:
Originally posted by KSTR
IME the very lowest order modes (say fundamental and second) are pretty close to MP. Then my goal is to setup the speakers and listening pos so as to have only boosts, not notches at those freqs and then apply reverse (MP) notch filters. The higher order stuff which is clearly not MP must be dealt with by room treatment and, again, optimized placement. Finally some gentle (broadband) overall EQ to get the amplitude response right.

- Klaus

For reference starting about 3/4 the way down.
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Old 26th July 2009, 05:47 PM   #100
gedlee is offline gedlee  United States
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Originally posted by john k...


Actually, as we discussed before Earl, in a typical room the source to listener transfer function is typically not minimum phase. The result is that tests such as those presented here do not correlate to amplitude response at all. It is not even clear that the smoothest amplitude response would necessarily yield the "best" transient, what ever that is?
Hi John

In general I agree, but the lower the frequency the closer it will be to MP. My comments here are stricktly limited to the very discrete modal region where the system is becoming close to MP. Much of the discussion is about HFs where everything changes, but my commenst are limited to the lowest frequencies.
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