Question regarding jumping distance with acoustic reference

[Mike0815]

Hello,

could someone help me understand why my setup does show different distance values for a constant speaker mic setup when using acoustic timing reference and not when utilizing loopback ?

My wiring with acoustic timing reference:
Out: Mac->HDMI->Receiver->PreOut-L-> ext.DSP_Ch1->Amp->speaker
Ref out: Mac->HDMI_7->Receiver->PreOut-Back_Surround-> ext.DSP_Ch2->Amp->tweeter
In: Mac<-USB<-Scarlett_2i2_Ch1<-Mic

When repeating measurements without any change in distance between mic and speaker or reference tweeter I get some millimeters variation. Interestingly some fixed ones like 2x 0mm, 3x 11mm, 4x 26mm etc. mixed with no apparent pattern.

My loopback setup:
Out: Mac->HDMI->Receiver->PreOut-L-> ext.DSP_Ch1->Amp->speaker
Ref out: Mac->HDMI_7->Receiver->PreOut-Back_Surround-> ext.DSP_Ch2
Loopback ref in: Mac<-USB<-Scarlett_2i2_Ch2<-ext.DSP_Ch2
In: Mac<-USB<-Scarlett_2i2_Ch1<-Mic

This shows basically no distance variations over lets say 10 measurements.
Shouldn't this be rather the way around with no common clock between HDMI and USB?

Regards
Michael

 

[John Mulcahy]

Would be handy to see an mdat file with some of the measurements.

 

[Mike0815]

Hello John,

thanks for your quick support.
Tried to generate mdat with that "issue" but could not reproduce it. Variations with acoustic timing reference are now max. 0.6 mm over 10 measurements so not relevant for my use case. Guess I made somethin wrong initially.
Or Focusrite fixed something with an update in the meantime…

Regards
Michael