Negative values at delay time measurement.

[Talisker99]

I tried to make a delay time measurement yesterday but the impulse response showed values below 0 meter. So I am oviously having a wrong reference. I include my preferenced, can sombody tell me my mistake ? thanx

 

[John Mulcahy]

Delays can be positive or negative relative to the reference. Select the actual devices, inputs and outputs you are using rather than leaving them as default.

 

[Talisker99]

Hey John, thanx for the reply but I just figured that I made a mistake when taking the screenshot. When I made the measurement I had chosen my Dante virtual soundcard as in and outputs. I you just imagine the DVS in every window instead of "default device" what could be the problem ? I did the same measurement with - I think- the same settings a week ago and it worked fine.

 

[John Mulcahy]

There isn't necessarily any problem at all. What is the actual delay figure you are seeing? What timing reference are you using? How have you connected to your system?

 

[Talisker99]

As far as I remember the source was approx 8m away and the measurement said something like -5u or so. the computer was connected by a Dante network with the settings that you see in the screenshot.

 

[John Mulcahy]

The soundcard settings don't indicate what timing reference was used. A loopback connection? Acoustic timing reference? Difficult to say anything about the delay without knowing what it is referenced to. It might be easiest to post the mdat file for a measurement.

 

[Talisker99]

Unfortunately I didn't keep any files from that measurement. But my reference is a loopback from the same desk output, that feeds the speaker system through the Dante network back into input 2 of the REW. At least that is what I intended to do but it is also where I think I made a routing mistake. I just don't seem to be able to pinpoint it.

 

[John Mulcahy]

Why not make a new measurement?

 

[Talisker99]

Well yes, my next show with that tour will be in two weeks, I'll give it another try and let you know what happens

 

[Talisker99]

So I tried again today and now I am sure that I am using a wrong path every measurement showed the same result so I am not measuring delay times, I am measuring something wrong I just can't work out, where the mistake is. I saved todays file and attach it.

 

[John Mulcahy]

Those measurements were made without a timing reference being used, so t=0 is placed at the IR peak. Note that phase will also be affected by starting the measurement so far up the range, it creates a sort of high pass effect. Best measuring full range.

 

[Talisker99]

but I used my input 2 of the DVS as a loopback from output 1 as a timing reference... or didn't I ?

 

[John Mulcahy]

You need to tell REW to use a timing reference, the selection is on the Measure dialog.

 

[Talisker99]

UUhhh found it..thanx I'm gonna retry tomorrow. But that window is rather new, isn't it ?

 

[John Mulcahy]

It was an Analysis preference in 5.19, been on the Measure dialog of the 5.20 beta releases for quite a while.

 

[Talisker99]

I didn't update for a long time ;-).... hope it works now, I will let you know

 

[Talisker99]

tadaaa... I knew it was something small and silly..so I picked the loopback as timing reference and I am back in the game. Thanx for your help.

 

[John Mulcahy]