REW Measurements sweeps not limited to frequencies defined. Intermittent distortion noted.

[Zedns7]

Hello All!
I am a newbie at REW. I have been playing with it for a week. These questions will probably be followed by others. I have done freq. response testing of outdoor speakers and Subwoofers outdoors and am now doing in situ tests.

While conducting these tests I was doing a measurement from 15 Hz to 200 Hz and I happened to have the tone generator window open at the same time. I noticed that the generator was actually showing which frequencies were being presented to the subwoofer during the sweep and even though I set it to start at 15 it started at 0 Hz! This also seems to be somewhat the case when I do pink noise tests. If I limit the pink noise from 20 Hz to 200 Hz, I still see frequencies under that being reproduced at very reduced amplitude. I have also noticed that if I first define a measured sweep in the generator and then do a measurement then it does adhere to the limits of the defined sweep, but this should not be required. Am I doing something wrong?

Also, some times I have noticed that the test signal distorts. This happens out of nowhere and is fixed by changing the outputs in the "Preferences" window. ALl I have to do is switch the output and then switch it back and then the distortion goes away. I save my speakers from the distorted signal by monitoring the acoustic reference, which itself is distorted when this occurs. Any ideas what may be happening? Any help would be greatly appreciated.

 

[John Mulcahy]

You can find the description of the measurement sweep in the signal generator and measurement help. The signal generator also describes the filtering for the random noise signals. If you need brickwall filter characteristics use the pink periodic noise signal.

No idea what causes the signal corruption. Perhaps if you have selected a different sample rate in REW to the rate the interface is configured for OS resampling might be a factor.

 

[Zedns7]

Thank you so much John. I really appreciate it. It seems I have to read the manual a little bit closer. Donating to show appreciation for the help and the great support.

 

[Zedns7]

So I read up on things and still don't understand why REW is presenting tones way below what I am defining. "The sweep will span the range from half the start frequency to twice the end frequency (with an overall limit of half the interface sample rate) to provide accurate measurement over the selected range." So if I define the sweep in the "Measure" module as from 20Hz to 200Hz, REW should present from 10 Hz to 400 Hz to the speaker. Instead it starts at 0 Hz and ramps up. I don't even think it goes to 400 Hz, but I know it goes to 200 Hz. Obviously, I don't want to present such low tones to my subs repeatedly, so can someone explain why this is happening and how I can stop it from doing so?

Sometimes when I do a measured sweep in the generator module it behaves the way it should but not when I run it from the measurement window.

Also, I do notice that the images displayed the help files are different than in my version of REW. I am not using the Beta version but REW 5.19. Should I be using the beta?

 

[John Mulcahy]

So I read up on things and still don't understand why REW is presenting tones way below what I am defining. "The sweep will span the range from half the start frequency to twice the end frequency (with an overall limit of half the interface sample rate) to provide accurate measurement over the selected range." So if I define the sweep in the "Measure" module as from 20Hz to 200Hz, REW should present from 10 Hz to 400 Hz to the speaker. Instead it starts at 0 Hz and ramps up.

The next sentence in the help explains: "If the start frequency is below 20Hz the signal begins with a linear sweep from DC to 10Hz, followed by a logarithmic sweep from there to the end frequency."

I don't even think it goes to 400 Hz

It does

Obviously, I don't want to present such low tones to my subs repeatedly

Why?

Also, I do notice that the images displayed the help files are different than in my version of REW. I am not using the Beta version but REW 5.19. Should I be using the beta?

The beta is what I would use.