- Thread Starter
- #41
You are welcome.Great explanation. Thanks. Frequency dependent damping of ultrasonic waves entering concrete behind steel would be another application next to Radar.
To repeat someone else’s question: How can these group delays be corrected? Does Dirac or Re-Phase do that? Or would one want to introduce certain group delays for a warm sound like harmonics with vinyl? Is a frequency sweep enough to characterize group delays or would one need to superposition for example a fixed frequency with a sweep?
There are a number of areas where this is important, including materials study as you mention, lidar/radar, broadband communications signals like spread-spectrum, and so forth. Not really my field so I do not claim competency.
As for correction, I do not know how (or if) it is done in audio programs. Several claim to adjust phase, not too difficult with a DSP, but I do not know the details. I believe Dirac Live does, as I had a Dirac Live AVP and am pretty sure it improved the group delay, and I know my SDP-75 (Trinnov) AVP improves group delay in my system. I do not know anything about RePhase. I would guess you could use something like a miniDSP to generate compensatory filters, again not something I have played with.
Nor do I have a feel for how bad it must be to be noticeable (audible); I suspect this is a non-issue for the vast majority of components, and speakers. IME a host of things we can easily measure are basically inaudible when the music plays unless they are horribly wrong (large, whatever).
Since you need to know phase shift over frequency a simple magnitude frequency sweep will not provide this information. A magnitude FFT of my two examples would look identical, for example. You need to a reference to capture changes in phase, or look at an impulse (or step) response, to determine group delay. I believe REW can (help) do it, by measuring group delay and calculating filters, but I have not tried recently.
HTH - Don