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Old 9th October 2012, 10:18 PM   #11
Elias is offline Elias  Finland
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And if you choose the multiresolution method you can visualise quite amount of more details: Here an animation of 'standard' wavelet CSD vs. multiresolution CSD of the same impulse response.
Click the image to open in full size.

CSD is good for detecting resonances from drivers, cabinets etc. It is also very good in analysing room reflections at high frequencies.

I never recommended CSD for bass.


P.S. Before anyone asks, that impulse response is from one of my long ago flooder tests. The ceiling reflection can be seen at 5ms.

- Elias
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Old 10th October 2012, 10:36 AM   #12
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I never recommended CSD for bass.
Pardon my ignorance but if that is true then what is this page about?
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Old 10th October 2012, 12:33 PM   #13
Rudolf is offline Rudolf  Germany
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Originally Posted by Elias View Post
Hey, you havent done constant Q yet !
Some more animated wavelets. I show the constant Q version with different amplitude scales (40/30/20 dB). Going below 40 dB helps to subdue the visual "noise" imho. 25 dB would probably show only those changes, which can be detected by the ear too. At least that's what I hear.

ani constQ wavelet.gif ani constQ wavelet 30.gif ani constQ wavelet 20.gif
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Old 10th October 2012, 12:58 PM   #14
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The 7ms reflection is now visible but where do all the other differences <7ms come from??
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Old 10th October 2012, 02:51 PM   #15
Rudolf is offline Rudolf  Germany
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Originally Posted by markus76 View Post
The 7ms reflection is now visible but where do all the other differences <7ms come from??
I don't know. Measurements were done with a peak volume of ~80 dB/1m. Note that many differences are below -30 dB. Maybe there was already some noise at 40 dB when I measured?

For the diagrams below I moved the microphone along the speaker axis from 0.5-2 m distance. Since the speaker is ~40 toed in, the move is somewhat diagonally across the room. So the timing of all reflections changes between the diagrams.
constQ 3 distances.gif
There is nothing special about the diagrams. Just showing how the wavelet diagrams change when moving from the direct field (mostly) into the reverberant.

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Old 11th October 2012, 04:05 PM   #16
Elias is offline Elias  Finland
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Originally Posted by markus76 View Post
Pardon my ignorance but if that is true then what is this page about?
In that page I show using modulated constant Q and ERB wavelets that a dipole bass reproduces the modulation envelope in a small room better than a monopole bass.


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Old 11th October 2012, 04:55 PM   #17
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In that page I show using modulated constant Q and ERB wavelets that a dipole bass reproduces the modulation envelope in a small room better than a monopole bass.


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"Better" as in "looks better" or is there any correlation to perception?
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Old 11th October 2012, 06:38 PM   #18
Elias is offline Elias  Finland
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This thread is about wavelet CSD, and not about modulation analysis.

But I just say that yes the perception is the key, and dipole wins in modulation reproduction ability in a small room.


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Old 12th October 2012, 04:17 PM   #19
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Would anybody like to comment on the different representations (conventional <-> wavelet CSD) and their usability for a critical analysis of loudspeaker room interaction?
Basically, a Wavelet CSD is a waterfall representation of filtered impulse responses.

Apply such a filter just before calculating the ETC, compute the envelope and you are at it. The only magic of wavelet CSDs is choosing the right filter.

BTW, when using a constant Q wavelet (which is essential constant bandwidth) I find it very useful to scale the time axis in periods, no seconds. Because two resonances with the same Q but different frequencies have different decay time, but normalized to periods they are identical.
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Old 13th October 2012, 10:16 AM   #20
Elias is offline Elias  Finland
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Originally Posted by Baseballbat View Post
Basically, a Wavelet CSD is a waterfall representation of filtered impulse responses.

Apply such a filter just before calculating the ETC, compute the envelope and you are at it. The only magic of wavelet CSDs is choosing the right filter.

BTW, when using a constant Q wavelet (which is essential constant bandwidth) I find it very useful to scale the time axis in periods, no seconds. Because two resonances with the same Q but different frequencies have different decay time, but normalized to periods they are identical.

The CSD is as the name suggest: Cumulative Spectral Decay.

I included CSD in my wavelet package since I thought people generally are more familiar with it than other types of wavelets.

CSD is good for some specific tasks. One has to be avare. It has constant energy along frequency axis but bandwidth and Q varies.

Constant Q is like an opposite of this.

These are all traditional wavelets.

Most useful for my purposes I have found wavelets that model some aspects of human psychoacoustics. These include Bark, ERB and Gammatone wavelets, for example.


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