Recent content by tony22

I don't use Perplexity at the moment, so I used ChatGPT. It told me what I already know about looking at these graphs.

Okay. Signals then, and not THD?

Okay, but when I do that, what am I looking for? Should I set up a narrow band of Pink Noise say from 20--100Hz and use RTA to look at it? Would I be looking at Distortion with RTA?

Okay. I'm flummoxed as to what it could be. Four sweeps. Five Seconds apart. No external audible intrusions whatsoever across all four sweeps. :scratch:

Clearly, I need a bit of learning in this area. :reading: Can you help me understand what could cause this degree of variation in the noise floor?

I trimmed it a bit. Maybe it will attach.

I guess it just bothers me. That's a >10 dB worsening of the THD in that range, when there was no change between sweeps. No HAVC (I'd turned it off before starting sweeps, as I always do). No vehicles outside. No lawn mowers. No airplanes. Nothing. I'd attach the mdat but I'm not sure it would...

You want the Impulse responses?

It's not the magnitude so much. It's the variation from sweep to sweep. Look at the first sweep. There's (compared to the next three) significantly less distortion in the 30-60Hz range. The question is - why?

Hi @John Mulcahy, I hate to keep nagging at this but I'm just confused. Is the UMIK-1 maybe just not a good device for measuring THD consistently? I ask because this morning I set up REW to take 4 consecutive sweeps, spaced 5 seconds apart, and this is what the THD plots look like (in order of...

John, the level was off. It was a bit higher. Could that explain what I'm seeing here? I'm about to do another run.

Thanks John. I will check as instructed. What worries me is that there's such a significant appearing difference. Nothing has changed in my system between these two measurements.

Oh, that was with my REL Carbon Special sub on. Here are the same before and after with sub off.

I've had no changes to my system since my last set of "reference" measurements. But after a rather nasty electrical incident I decided to run new sweeps and compare them to my references. I set up my UMIK-1 in its standard position (it's always in the same place, +/- 1/4-1/2"), and set the...

Got it. Certainly for developing convolutions I do separate L and R channels, and for doing detailed acoustical measurements (I've worked with John Dykstra at GIK in the past). Once in a while though doing a "quick" two channel measurement is... well, quick. :)