[Lumen]

I'm new to time-domain measurements and have a question, because most of the time I take things literally. But first, some background:

It's no secret REW is able to use timing references in measurements to calculate system delays so that separate measurements have the same absolute timing. That's useful when trying to time-align different drivers in the same cabinet, or different speakers in a room. For REW, a timing reference can be a soundcard loopback connection or an acoustical reference. Austin Jerry's Guide states on pg. 91 that Impulse Response measurements are only meaningful if the original measurements were taken using an acoustic timing reference. I was under the impression that a loopback timing reference was sufficient. From what I can tell, setting up an acoustical timing reference seems much harder.

Can anyone please help answer my questions:

1. True or False? If only SPL & phase is being measured, a loopback is not needed.
2. What is the "original measurement" referred to in the guide?
3. Under what conditions is an acoustical timing reference needed vs. a loopback one?

 

[Wayne A. Pflughaupt]

1. Yes.

2. Probably means that if try to go back to a previous measurement and use it to generate a IR graph, the original measurement had to have been made with whatever reference he’s referring to, even if it was just SPL.

3. Mr. Myers knows much more about this stuff than I do. Hopefully he will weigh in. I have little interest in time domain measurements myself.

Regards,
Wayne

 

[JohnM]

An acoustic reference is needed when a loopback isn't possible, such as when using a USB mic.

 

[Lumen]

See? This is what I love about HTS - prompt, expert help. Thank you both!:T

1. Yes.

As I suspected, so thanks for confirming.

2. Probably means that if try to go back to a previous measurement and use it to generate a IR graph, the original measurement had to have been made with whatever reference he’s referring to, even if it was just SPL.

Again, thanks for confirming my suspicions. If you intend to study time-domain functions then plan on a using a timing reference for all measurements.

An acoustic reference is needed when a loopback isn't possible, such as when using a USB mic.

Seems obvious to me now. Thanks for taking time to answer such a basic question!