Timing References; 2-chnl Loopback vs Acoustic

[EarlK]

Hi,

Please excuse my ignorance here ( since I've never before explored using the Acoustic Timing Reference feature ) but is it normal REW behavior for the distances derived from using the Acoustic Reference to not equal those gotten from the 2-chnl wired ( loopback ) reference ?

When I compare the two, the Acoustic reference returns a consistently shorter distance ( by slightly over 8 inches ).

This is with the HF reference tone being played on the same channel being measured .



PS;I'm running the latest 5.20 Beta, Version 4 ( on Windows 10 Pro ).

 

[jtalden]

The wired loopback reference time is basically immediate so the measurement impulse position includes the entire time of flight of the sound to the mic.
The acoustic reference time is when the reference sound arrives at the mic. So the only way the measurement impulse position will be similar with wired loopback is when the reference speaker is very near the microphone and thus almost immediate.

So if the same TW is use for both acoustic reference and for measurement then the measurement impulse will be very near 0 ms. no matter how far the TW is to the mic.

 

[EarlK]

Thanks John for responding.

I do see that if the same tweeter is used as the marker reference and as the driver under test, then the distance returned is constant ( I just proved that to myself by adding 10ft to the test mic distance and the so-called distance didn't change ).

I think I get it now.

Cheers, Earl