Loopack vs Acoustic Timing Reference for Phase Measurement

fus

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I'm doing some FIR filters for my speakers and i'm using REW and rePhase for this purpose. However i found out that depending on the time reference i've use i get very different results of the Phase and the Impulse Response. Attached are screenshots. Both measurements are done using UMIK and are done on the exact same location. The only difference is the timing reference method. Why i'm getting such difference and which one i should trust?
 

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John Mulcahy

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Looks like your loopback path may be inverting. A loopback cannot be used as a timing reference for a USB mic because it is on a different device, devices do not maintain any synchronisation relative to one another.
 
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Harrycr

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Hi John
Is it ok to leave the loop back cable connected on a sound card for all measements?
Also do I still have to do the sound card calibration with the loop back cable connected?

Thanks
 

John Mulcahy

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Is it ok to leave the loop back cable connected on a sound card for all measements?
Also do I still have to do the sound card calibration with the loop back cable connected?
This thread is a question about using a UMIK for measurement, if your question is not about using a UMIK best starting a separate thread to avoid confusion.
 

fus

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Looks like your loopback path may be inverting. A loopback cannot be used as a timing reference for a USB mic because it is on a different device, devices do not maintain any synchronisation relative to one another.
Thanks for the prompt reply!
 
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