A question about RTA in REW

[jorge chia]

Hi everyone,

Can anyone explain what the three numbers in the attached image mean?

 

[DanDan]

Yup the C Filter is a curve which represents how the ear hears at quite a high level, say over 85dB. The A filter does the same but way down around 40dB where we are really very deaf to LF.
More formally. https://www.engineeringtoolbox.com/decibel-d_59.html

 

[jorge chia]

Yup the C Filter is a curve which represents how the ear hears at quite a high level, say 85dB. The A filter does the same but way down around 40dB where we are really quite deaf to LF.

thanks for the quick response. Is this what is referred to as C-weighting and A-weighting when talking about spl meters? also, is the big number up top the peak spl measurement?

 

[DanDan]

You are welcome. Indeed they are. dBC and the like are defined scientific terms wherever they occur. Peak SPL is also a defined term, and there are many others, e.g. LAFmax! Check the REW manual to see what that changing number means. I suspect it is Lp, i.e. Sound Pressure Level averaged over the last Second if Slow weighting is used. Similar to the changing number you would see on the SPL Meter, but with Zero or no frequency weighing.

L : Sound and Vibration Terms and Definitions

alphabetic list of sound and vibration terms, this page defines the L words

www.acoustic-glossary.co.uk

 

[John Mulcahy]

From the RTA help for that version:

The current Input RMS value is shown to the left of the record button, in dB SPL or dBFS according to the setting of the Y axis. This figure excludes any DC content in the signal. A and C weighted values are shown below the unweighted rms figure. If clipping is detected in the input the RMS value turns red.

 

[jorge chia]

So if i'm analyzing a scene from a movie for instance, the unweighted rms number tells me an average over the last second like DanDan mentioned? is this an average throughout the entire frequency range or only the range that i have set in the RTA window?

 

[John Mulcahy]

The RMS figure is for the number of signal samples selected as the FFT length. It is not affected by the frequency span you choose to look at.