struggling with timing and time references

[baskind]

Dear all,

I've been using REW for a while for Room T60 measurements and (wonderful) waterful plots. Now I'd like to go a little bit further in detail with measurements and I'm facing timing problems I don't understand. I'd like to keep the trickiest one with loopback for a next thread (or maybe at the end of this thread) and focus on the basic problem I encountered on a simple example:

. create an artificial impulse reponse as a delayed dirac impulse, for instance with a delay of 4800 samples by 48 kHz, also 100ms. The impulse is followed also by silence, for instance 1 sec (48000 samples)
. import it in REW 5.19 beta 8 => The impulse is put back to the time origin, the 100ms delay just disappeared! Consequently, the group delay, that should be constant and equal to 100ms, shows 0 for the whole range

Can someone explain me why?

All the best,

Alexis

 

[baskind]

Found it: in "Preferences => Analysis", the option "For imports set t=0 at impulse peak" was check, instead of "For imports set t=0 at first sample". And "Set t=0 at IR peak" is also checked by default.

Alexis