HOLMImpulse: Measuring Frequency- & Impulse-Response - Page 49 - diyAudio
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Old 15th October 2009, 02:20 PM   #481
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Lightbulb 1/N-Octave smoothing <=> Frequency dependent window

New version:

Version 1.4.1.4 (2009-10-15)
Bugfixes:

* Factor of 2 when calculating 1/N octave filters
* Show legends on butmaps can be unchecked
* Invert amplitude causes normalization to be invalid

New User Guide with Mathematics v0.0.6:
http://holmacoustics.com/holmimpulse.php

Or

HOLMImpulse > Help > 'User Guide (Checks for update)'

on page 15 to 22 I derive why:
1/N-Octave smoothing <=> Frequency dependent window
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Old 15th October 2009, 05:16 PM   #482
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Originally Posted by askbojesen View Post
New version:

n page 15 to 22 I derive why:
1/N-Octave smoothing <=> Frequency dependent window
Problem downloading user's guide pdf
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Old 15th October 2009, 05:29 PM   #483
gedlee is offline gedlee  United States
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Originally Posted by john k... View Post
Problem downloading user's guide pdf
Worked for me. I read the section in question and remain unconvinced. In fact his own example shows how the smoothing rejects the delayed noise. The point here is that in this example thats what you want, but what if there is some delayed diffraction effects - they shouldn't be rejected by the smoothing, but they will be with this technique.

The math only shows how a filter in the frequency domain has an analog as a window in the time domain. It does not prove that the two things will yield the same results for a spectral smoothing done as suggested in this discussion. I think that its clear that they won't.
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Old 15th October 2009, 05:44 PM   #484
soongsc is offline soongsc  Taiwan
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So if they don't yeild the same results, what advantage does one have over the other? Why would we want it one way or the other?
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Old 15th October 2009, 05:50 PM   #485
gedlee is offline gedlee  United States
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So if they don't yeild the same results, what advantage does one have over the other? Why would we want it one way or the other?
Clearly the time domain windowing is going to make a speaker look better. Its advantage is that its easy.

Take for example a mouth reflection from a waveguide. These are delayed in time and will therfor be cut-off at some point by the shortened time window at higher frequencies when smoothing is applied per the technique shown here.

Last edited by gedlee; 15th October 2009 at 05:52 PM.
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Old 15th October 2009, 06:10 PM   #486
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Well I have found the smoothing to be closer to what I actually am hearing. Couldn't this be useful for at least getting an approximation of the way we actually hear things in a room? That is what I have been using it for personally so I don't see the smoothing as useless exactly. Maybe not totally accurate because as you point out you are probably throwing away some audible artifacts along with some of the reflections that I don't normally hear. But I guess I just don't find the reflections that a mic picks up exactly useful to what I am testing for.
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Old 15th October 2009, 06:24 PM   #487
gedlee is offline gedlee  United States
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Well I have found the smoothing to be closer to what I actually am hearing. Couldn't this be useful for at least getting an approximation of the way we actually hear things in a room? That is what I have been using it for personally so I don't see the smoothing as useless exactly. Maybe not totally accurate because as you point out you are probably throwing away some audible artifacts along with some of the reflections that I don't normally hear. But I guess I just don't find the reflections that a mic picks up exactly useful to what I am testing for.
My data says the exact opposite. Group delayed signals are highly audible, increasing in audibility at higher SPLs. This effect would be ignored with the time domain windowed technique, but not with a true frequency averaging (albeit this kind of thing is never highly significant in the frequency domain). "Smoothing" makes a lot of sense, but not if it rejects signal components that we know cause audible artifacts.
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Old 15th October 2009, 06:38 PM   #488
Key is offline Key  United States
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I just am not sure about a lot of things which people claim are audible. My system seems to be immune to all types of things most experts claim should be audible. But I am still testing so no conclusions on group delay and diffraction effects yet.
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Old 15th October 2009, 07:07 PM   #489
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Question How do you smooth ?

Quote:
Originally Posted by gedlee View Post
The point here is that in this example thats what you want, but what if there is some delayed diffraction effects - they shouldn't be rejected by the smoothing, but they will be with this technique.
How do you smooth?

Please reveal your formulas, so I can implement your method
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Old 15th October 2009, 07:14 PM   #490
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