requesting help with troubleshooting REW

[Bas de Rooij]

Greetings

i hope someone can help me out with this one. In the included screenshot and MDAT file, you can see that the measurement seems highpassed with a very steep filter at about 3.5KHz. But i have no filters engaged in the signal path, at least not that i'm aware off. The sweep sounds and feels full range, the house shakes in the start of the sweep. The inputs are selected directly and there are no plugins inserted anywhere in the Apollo mixer (screenshot included). I think most relevant info is visible in the screenshot and MDAT. I can add that the speakers are Neumann KH310's and that in this measurement only the left speaker was switched on. I've checked the mic and speakers with a separate tone generator and RTA. The problem is not present in that scenario: those measurements are full scale, as you can see included screenshot. So, does anyone have an idea of what's going on here? why do i only have a partial measurement?

 

[John Mulcahy]

The signal is also really noisy and has a lot of late arriving energy, the rise is much less steep when the right window is extended to include that. Maybe there is some strange latency issue, could try measuring with a timing reference.

 

[Bas de Rooij]

Hi John!

Thanks for your reply, the late arriving energy might be because this is a measurement of an empty room. I want to make baseline measurements before i put my desk in and start treating the room. I'll try making measurements with the lowest possible buffer size, now it's at 64 samples, i can go lower. I'll have to do the measurements tomorrow, because it's past midnight here atm.

The noise might partially because it's very windy outside and i'm in a simple bedroom. Background noise is about 42dBC. I'm doing the measurements at 80dBC (slow) to try and get a decent SNR. For real measurements i guess i'll have to wait for a more silent moment. I just checked the mic's signal on headphones and the mic's electronics are pretty noisy compared to a mic i know to be silent which i connected to the same channel.

Could you maybe tell me where to find an article about setting up the latency compensation? I tried setting up the loopback measurement, but without success.

Thanks again

 

[John Mulcahy]

Probably easiest to use the acoustic timing reference, just select that on the Measure dialog and set the speaker you are measuring to be the ref output.

 

[Bas de Rooij]

these are measurements with the acoustic timing reference enabled, the red one is the Apollo, the green one is an old M-Audio interface. These are still very odd measurements. Should i hear a spike or anything before the sweep when the acoustic reference is enabled? I didn't hear anything extra.

 

[John Mulcahy]

The acoustic reference is a short high frequency sweep, 5 kHz to 20 kHz, so you should hear that before the main sweep starts. You could post an image of the REW Soundcard preferences and the Measure dialog for a check of the settings.

 

[Bas de Rooij]

I didn't patch the reference output right. But now i did and it indeed was the key to correct measurements. So thanks again!