SPL & Distortion

[2206]

I noticed that the SPL level in the SPL window and in the Distortion window are not alike. The SPL window shows higher dB values - 10dB or more - than the fundamental in the Distortion window. What is going on? Thanks in advance!

 

[EarlK]

I've never seen that problem occur in any of my REW experiences.

Can you post pics to demonstrate this anomaly ?

 

[2206]

Voila
SPL and distortion window
SPL window gives about 90dB.
Distortion window is more like 70dB for the fundamental.
Distortion (dB SPL) is at around 30-40dB or about 30-40dB below the fundamental.
How is the fundamental defined? Apparently adding 30-40dB of distortion to 70dB fundamental does not give the 90dB in the SPL window...
Thanks in advance

 

[EarlK]

Thanks!

I've never seen REW do that ( though I have indeed seen it not perform quite as expected ).

IF you happen to have 2 copies of REW residing on your computer, I'd suggest getting rid of the oldest one .

( From experience ) having 2 copies of REW on my computer has resulted in some ( very hard to trace ) anomalies .

Another thing to try is to delete your Preferences ( & shut Down REW ) & then reopen the program ( you'll of course send REW back to it's default preferences ).

 

[2206]

Can't find the pref. file? Is there a uninstall app for REW? Thanks!

 

[EarlK]

I believe there's an uninstall app included with every REW Windows installation.

Typically ( in Windows ), right-clicking on the application's tile ( found in the Start menu or listing of all applications ) will display a handful of choices ( of what to do with the app. ).
- "Uninstall" is typically one of those choices listed.

 

[2206]

I am on a Mac...

 

[Matthew J Poes]

Voila
SPL and distortion window
SPL window gives about 90dB.
Distortion window is more like 70dB for the fundamental.
Distortion (dB SPL) is at around 30-40dB or about 30-40dB below the fundamental.
How is the fundamental defined? Apparently adding 30-40dB of distortion to 70dB fundamental does not give the 90dB in the SPL window...
Thanks in advance

I've never seen that either, John would be best to chime in on this. The distortion plot is clearly wrong as it shows your noise floor as residing near the residual of the electronics practically. If you actually had a room that quiet, you quite literally would have built an anechoic chamber. Having a noise floor below 10db's (even 0db's at places) is what test facilities go for (and many don't achieve). It appears that you could add 20db's to each of these values and get you back where you should be.

Is there any chance you accidentally applied some shift to the amplitude? Is this shift always present in every measurement no matter what you do? Like if you took 5 measurements in a row, don't touch anything, go straight to the distortion plot, it would show that same behavior?

 

[2206]

I have seen this for several days now, that is after power down and restart. As I could not make sense of it, I thought I'd check with the experts. I am new to REW. I am using REW V5.19 Beta 8 on Mac.

 

[Greg Dunn]

To uninstall on a Mac, just drag the app to the Trash. You can use the "delete preferences and shut down" option when you quit the app, delete it and then install a known up to date version if you want to be certain you have cleaned up any issues.

 

[EarlK]

I'd do as Greg suggests ( "delete preferences", shut-down REW, then delete REW by dragging its complete folder to the trash & then re-install REW ).

 

[2206]

Wow, that did it! SPL is the same in SPL and distortion window. Noise floor is at around 22dB and climbs to 50dB at the low end. RTA is similar, a little lower. Thanks a lot. Cheers!

 

[Matthew J Poes]

Wow, that did it! SPL is the same in SPL and distortion window. Noise floor is at around 22dB and climbs to 50dB at the low end. RTA is similar, a little lower. Thanks a lot. Cheers!

Great, that sounds much more reasonable.