Hello. I have a question.
Now, mind that these specific ones are measurements I did in october 2023. Forgot to ask at the time.
Files says it was REW 5.20, I presume the one that was up to date at the time (V5.20.13?), so don't know if something changed after)
I don't have the setup rigged right now, will have to measure soon and that's why I am asking.
I am using what would be called a full dual channel rig to measure loudspeakers.
So I am feeding back the signal from the amp output (padded by a resistor probe).
The sound card is a focusrite scarlett 2i2 3rd gen and it goes pretty much like this (using the 2i2 internal mic preamp obviously):
I've got a turntable and I do the sweeps around a speaker (just 180deg when it's simmetrical).
Rew is set to repeated measurements with some seconds of delay between them just to allow me to rotate the turntable.
I pretty much follow the vituixcad paper for all rew settings: https://kimmosaunisto.net/Software/VituixCAD/VituixCAD_Measurement_REW.pdf
Those instructions say that once you do the full set of measurements, you set the IR window in the 0 degree (on axis) measurement and "apply windows to all".
So I set the impulse window on the 0 degree measurement and apply windows to all... and it's usually ok.
But on some sets of measurements (same day, same place, same rig etc) I realized that (I measure every 10 degrees) there will be a measurement that will have the impulse placed like at around -11.5ms instead of 0, compared to all the others in the set.
e.g. you can easily spot the 11th measurement (110deg hor) here is the black sheep after applying the IR window to all:
Note that while doing these measurements the microphone doesn't move nor the speaker, the driver is centered on turntable axis, so distance is more or less the same.
Here you can see the first 0deg measurement (on axis) with ref time at 0:
(ignore that's wired inverted)
and here is the 11th one (110deg hor) with the different ref timing. The first impulse here it is at -11,5ms compared to others, so the window is applied at wrong place.
So I manually fix that one and then it's good.
Or I redo the measurement individually and it'll usually pick the correct one the second time.
I thought it was aligning on the reflection as the height of the reflected one is greater?
But the issue is that there are other measurements where the reflected impulse is stronger than the direct one and the thing didn't happen...
eg. the one after, the 12th (120deg hor) was correct yet the reflected IR was higher
Now sometime I have full sets of repeated measurements without any issue, and sometime I get one or two measurements like this in a set.
It's kind of random.
What is causing this? Is there some setting I am missing? What I am doing wrong?
Is it rew offsetting the thing or it's an hardware/software issue in the drivers/soundcard/OS chain?
(windows 10, focusrite 2i2 usb on asio drivers)
As I said this is a chain of automated "repeated measurements". Nothing is changing between them software wise. I launch the thing and just have to rotate the turntable.
Shouldn't always get the correct timing from the loopback with those settings?
these are the settings that vituixcad recommends and that I used:
Is there something wrong in my settings for this full dual channel measurement setup?
these are vituixcad suggested settings for the analysis tab, i think I run it exactly as recommended:
thank you
Now, mind that these specific ones are measurements I did in october 2023. Forgot to ask at the time.
Files says it was REW 5.20, I presume the one that was up to date at the time (V5.20.13?), so don't know if something changed after)
I don't have the setup rigged right now, will have to measure soon and that's why I am asking.
I am using what would be called a full dual channel rig to measure loudspeakers.
So I am feeding back the signal from the amp output (padded by a resistor probe).
The sound card is a focusrite scarlett 2i2 3rd gen and it goes pretty much like this (using the 2i2 internal mic preamp obviously):
I've got a turntable and I do the sweeps around a speaker (just 180deg when it's simmetrical).
Rew is set to repeated measurements with some seconds of delay between them just to allow me to rotate the turntable.
I pretty much follow the vituixcad paper for all rew settings: https://kimmosaunisto.net/Software/VituixCAD/VituixCAD_Measurement_REW.pdf
Those instructions say that once you do the full set of measurements, you set the IR window in the 0 degree (on axis) measurement and "apply windows to all".
So I set the impulse window on the 0 degree measurement and apply windows to all... and it's usually ok.
But on some sets of measurements (same day, same place, same rig etc) I realized that (I measure every 10 degrees) there will be a measurement that will have the impulse placed like at around -11.5ms instead of 0, compared to all the others in the set.
e.g. you can easily spot the 11th measurement (110deg hor) here is the black sheep after applying the IR window to all:
Note that while doing these measurements the microphone doesn't move nor the speaker, the driver is centered on turntable axis, so distance is more or less the same.
Here you can see the first 0deg measurement (on axis) with ref time at 0:
(ignore that's wired inverted)
and here is the 11th one (110deg hor) with the different ref timing. The first impulse here it is at -11,5ms compared to others, so the window is applied at wrong place.
So I manually fix that one and then it's good.
Or I redo the measurement individually and it'll usually pick the correct one the second time.
I thought it was aligning on the reflection as the height of the reflected one is greater?
But the issue is that there are other measurements where the reflected impulse is stronger than the direct one and the thing didn't happen...
eg. the one after, the 12th (120deg hor) was correct yet the reflected IR was higher
Now sometime I have full sets of repeated measurements without any issue, and sometime I get one or two measurements like this in a set.
It's kind of random.
What is causing this? Is there some setting I am missing? What I am doing wrong?
Is it rew offsetting the thing or it's an hardware/software issue in the drivers/soundcard/OS chain?
(windows 10, focusrite 2i2 usb on asio drivers)
As I said this is a chain of automated "repeated measurements". Nothing is changing between them software wise. I launch the thing and just have to rotate the turntable.
Shouldn't always get the correct timing from the loopback with those settings?
these are the settings that vituixcad recommends and that I used:
Is there something wrong in my settings for this full dual channel measurement setup?
these are vituixcad suggested settings for the analysis tab, i think I run it exactly as recommended:
thank you
