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Author Topic: SQ/AR2412 Traces  (Read 893 times)

Mark Wilkinson

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Re: SQ/AR2412 Traces
« Reply #10 on: July 24, 2018, 11:00:07 am »

I think I found what you are talking about.

http://www.rationalacoustics.com/forums/showthread.php?1094-ref-to-gen-delay-time-problems

"Transfer Function measurements can also be referenced internally to Smaart's signal generator by enabling "Allow Multi-Device Transfer Function"

Mark, good discussion. I agree with your math. 1/8" seems about right.

Does that mean that we can't measure up to 20kHz phase response accurately? Or am I missing something with the REW discussion?

Can someone explain in more layman's terms how subsampling works? Is it simply using interpolation between samples to obtain the expected value?

Nathan, excellent find.   I had no clue that's what Multi Device Transfer could do..
Seems I need to be hitting the manuals harder !

I think with Smaart, we can measure 20kHz accurately, to no worse than 1/2 sample off, at 48kHz (assuming we are using MTW transfer windowing with its 48k requirement.)
So this is the same 75 degrees from 96k sampling numbers above....which means to me, and I see every now and then based on random luck with mic position, that if the mic just happens that it's positioned halfway between inferred sample timing, the phase trace at 20kHz will tail upwards from flat by about 30 degrees, or downwards by 30 odd degrees, as we bump delay finder one sample.

Obviously a sample off is no big deal in the real world at all...heck, I was trying to locate a line array last week and couldn't even pin the damn thing to within 30 samples.   
I just love precision and knowing how things really work....

My take on sub-sampling is that it just re-samples the impulse response, keeping the mag and phase relationship through the spectrum the same, while forcing the very upper end of the freq spectrum (nyquist freq maybe) to zero degree phase.
But that take is just one hell of a layman's guess ....
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