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How can I get good coherence in FFT measurements

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Riley Casey:
If you've ever tried to tune a system without quiet time built into the production schedule you'll know what I mean. That plus air handling noise and such its just a more energy arriving at the mic means better signal to noise thing.



--- Quote from: Russell Ault on May 03, 2024, 12:51:24 PM ---I'm not sure I understand this one; other than helping to out-compete any ambient noise, how does using a louder test signal improve coherence?

-Russ

--- End quote ---

Russell Ault:

--- Quote from: Riley Casey on May 03, 2024, 01:09:38 PM ---If you've ever tried to tune a system without quiet time built into the production schedule you'll know what I mean. That plus air handling noise and such its just a more energy arriving at the mic means better signal to noise thing.

--- End quote ---

Ah okay, so it is just about out-competing ambient noise; makes sense!

(I tend to conceptualize the "near field" of a speaker as being more about direct-to-reverberant ratio instead of signal-to-noise ratio, and was therefore confused by the idea of "moving the near-field by adding level" since the reverberant characteristics of a room are level-agnostic.)

-Russ

Tim McCulloch:

--- Quote from: Russell Ault on May 03, 2024, 09:43:39 PM ---Ah okay, so it is just about out-competing ambient noise; makes sense!

(I tend to conceptualize the "near field" of a speaker as being more about direct-to-reverberant ratio instead of signal-to-noise ratio, and was therefore confused by the idea of "moving the near-field by adding level" since the reverberant characteristics of a room are level-agnostic.)

-Russ

--- End quote ---

What you said.  I've found that 6dB above ambient is more than sufficient to provide coherency; even mixing in a little pink noise with the pre-show music will increase coherency.

Increasing the pink noise level will do nothing for reflection-induced incoherence.

Russell Ault:

--- Quote from: Tim McCulloch on May 04, 2024, 10:23:21 AM ---{...} even mixing in a little pink noise with the pre-show music will increase coherency. {...}

--- End quote ---

You just need to find music that has a more broadband spectral make-up; thrash metal, maybe?  ;D

-Russ

Riley Casey:
IOW music that's so close to pink noise the difference is negligible to software ...


--- Quote from: Russell Ault on May 04, 2024, 05:05:44 PM ---You just need to find music that has a more broadband spectral make-up; thrash metal, maybe?  ;D

-Russ

--- End quote ---

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