Some problems about time and phase workaround (and other)

[bobolix]

I'm quite new at the REW though, but I got couple tens of years experience with acoustic measurement. I appreciate very much the effort of Mr. Mulcahy and I must say the REW is a very powerful instrument. Nevertheless, I found several problems working with REW.

1. Trying to enter the offset value manually (i.e. numerically) I found only the whole numbers are accepted and if the value is entered in decimal format with comma it is ignored. It is quite unpleasant, as the setting by slider is quite coarse.

2. The calculation of the phase doesn't reflect the window position (the way as I'm accustomed at the DRA MLSSA). In fact the position as well as the window length and type isn't reflected for the phase at all, the window is applied only for the calculation of the magnitude and/or SPL.

3. For the measurement only sweep is available, which is only modestly configurable, the noise offer is inactive - being planned for the further beta versions maybe.

 

[John Mulcahy]

1. Trying to enter the offset value manually (i.e. numerically) I found only the whole numbers are accepted and if the value is entered in decimal format with comma it is ignored. It is quite unpleasant, as the setting by slider is quite coarse.

I guess your are referring to the t=0 offset slider. Try using a decimal point instead of a comma, it may work better, but the easiest way to make fine adjustments to the value is to use the left and right arrow keys, per the help.

2. The calculation of the phase doesn't reflect the window position (the way as I'm accustomed at the DRA MLSSA). In fact the position as well as the window length and type isn't reflected for the phase at all, the window is applied only for the calculation of the magnitude and/or SPL.

That would be equivalent to only allowing windows that are referenced to t=0, which is an unnecessary restriction that would prevent some types of analysis. The t=0 controls define the reference time, the window controls select which portion of the signal to analyse, which may be referenced to time zero or may be referenced to some other time in the signal (the time of the peak, for example) as required.

3. For the measurement only sweep is available, which is only modestly configurable, the noise offer is inactive - being planned for the further beta versions maybe.

Yes, though aside from environments with high levels of impulsive background noise the sweep will perform best anyway.

 

[bobolix]

Thak you very much. Nevertheless, I don't understand why the numbers with comma are not accepted, if e.g. at IR window setting the comma or point are accepted both.

 

[bobolix]

I found after some fiddling that the independence of the window setting and time offset in context of the calculation of the phase is quite useful. Namely I can apply the time offset first and then set the IR window to obtain the best result. The only drawback appears at using of the frequency dependent window, which starts in the reference time (I work with this option usually). The position of the IR relative to the window is affected by the time offset, so that its position relative to the IR window start changes if the time offset is changed, and the SPL response is then affected also by the time offset. However this is no serious problem. Thank you again !

 

[bobolix]

Yes, though aside from environments with high levels of impulsive background noise the sweep will perform best anyway.

If the noise signal option should be activated in future, then IMHO the good measurement signal would be the also the cycled (i.e. repeated) pink noise or the "pinky weighted" MLS signal (as the standard MLS signal or the white noise contains mainly the high frequencies, which isn't favourable under noisy conditions).