Measuring phase of harmonics in an amplifier

[wtnh]

Hi - I am relatively new to REW. It is a spectacular piece of software, but a bit daunting for noobs like me.

I am using 5.19 on a Macbook Pro running Catalina. I am building an amplifier and have successfully used the REW RTA for distortion measurements on the amp.
The audio interface is an old EMU 0404 USB with updated macOS drivers. I would like a way to visualize the relative phase of harmonics vs. the fundamental. Is there a way to do this in REW, perhaps with the filter components?

By way of further explanation, I am using differential inputs to the EMU from the amp output (with dummy load). When I view the RTA and open the distortion panel, I can see the phases of the harmonics (which I assume are relative to the fundamental). But if I reverse the differential signal, all the harmonics flip from negative to positive, with no indication that the phase of the fundamental has flipped. I discovered this by accident when I reversed the differential leads.

So I am wondering how this might be measured - perhaps with the scope option in the new beta?

Thanks - it is truly a great piece of software!

 

[John Mulcahy]

The harmonic phases are relative to the fundamental. To see the absolute phase of the fundamental of the output relative to some input signal it is probably easiest to put them on different input channels and use the scope.

 

[wtnh]

The harmonic phases are relative to the fundamental. To see the absolute phase of the fundamental of the output relative to some input signal it is probably easiest to put them on different input channels and use the scope.

Makes sense - I'll give that a try. I had difficulty with the new beta version (mentioned in another thread) picking up the input from the EMU, so I reverted to V5.19. But I'll try the new version again and see if I can resolve the issue. I see the new version has a scope feature - wondering if I could use that to try your suggestion?

 

[John Mulcahy]

Sure, I meant the REW scope.