Strange decay times issue
Old 30th December 2012
  #1
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Aaron Miller's Avatar
 

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Strange decay times issue

Does anyone know if the following decay times (which appear to be increasing in the lowest frequencies) can occur naturally? Or have I definitely botched the setup in some way?

Before treatment:



After treatment:



The dark blue here seems weird.
Old 30th December 2012
  #2
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Ethan Winer's Avatar
 

Lightbulb

I've never seen this, though I don't use FuzzMeasure. Swelling after decay might be possible in a very large room as reverb. I honestly don't know. Have you contacted Chris Liscio?

--Ethan

The Acoustic Treatment Experts
Old 30th December 2012
  #3
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Pretty interesting!

I'm no expert, but is there anything in your room that resonates at a low frequency, like an unmuted kick drum, maybe a piano, empty 50 gallon drum, adjacent cement staircase/hallway?

I don't know that it would generate enough tone to be picked up at those levels, but maybe.

Please keep us updated on what you find!
Old 30th December 2012
  #4

What do you get if you disconnect the speaker and run this? Does the blue stuff show up with no actual excitation?



-tINY

Old 30th December 2012
  #5
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I also don't use fuzzmeasure, so I don't have anything to add on the software setup.

However, are you sure there is no low freq AGC (auto gain control, compressor?) somewhere in the input chain? What mic, pre-amp/soundcard set up are you using?

The only other thing I can think of is some low level external noise that may have been picked up ie other than the test sweep. Have you tried the same set up in another room? If you get the same LF late onset increase in level then there is probably something wrong with your set up?
Old 30th December 2012
  #6
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Aaron Miller's Avatar
 

Thread Starter
I believe it was user error: the gain on the loopback channel (ie, channel 2 output into channel 2 input; used for measuring the internal delay and FR of my interface and compensating accordingly was set too low). Now it's set appropriately, I'm getting consistent decay in the sub 100Hz region. Must have been that.
Old 31st December 2012
  #7
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Glad you got it sorted out!
Old 31st December 2012
  #8
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DanDan's Avatar
Loopy

For the vast majority of everyday operation, Loopback correction is not necessary. If you need extra S/N ratio, use longer sweeps. That is just as good as multiple ones combined. But lose the Loop.
If you see those odd cut off blurps at the front of the graph, i.e. end of decay, make the IR window longer, as long as the graph axis if necessary. That will clear it up.
DD
Old 31st December 2012
  #9
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Aaron Miller's Avatar
 

Thread Starter
Ahhh, okay. Thanks for the tip!
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