dBFS Level Question in Generator and Measurement

[dcashel]

Hi all,

I am just started to use REW and have the following question. I am using REW version V5.19.

I plan on using the Generator and SPL Meter in REW to set the output level off all my speakers to 75dB before doing any measurements.

Does the RMS Level(dBFS) value in the REW Generator and the Sweep Level (dBFS) value when doing a Measurement have to be the exact same value? I noticed that the REW Generator has a RMS(dBFS) default value of -20 whereas the REW Measurement Sweep Level(dBFS) has a default value of -12. Do these values have to be set to the exact same value or should I just use the default values?

Thanks so much for the help....

 

[John Mulcahy]

Generally best having your system volume set as you would normally use it then adjusting the generator level to get the desired 75 dB SPL with whichever speaker you choose to act as the reference, e.g. left front. Then leave the generator level alone to check the other speakers and adjust their trims as required. Measurement sweeps can then use the same level to get sweeps that will be at around 75 dB.

 

[dcashel]

Thanks for the help. Before your comment I was going to just leave the Generator and Measurement sweeps levels at there default dBFS values and adjust my AVR volume until the SPL read 75 dB. But, I will follow your instructions instead.

 

[dcashel]

Which smoothing in REW is recommended when looking at frequencies below 100Hz and above 100Hz?

 

[Drew Neilson]

Funny, your question about the RMS Level value in the REW Generator and the Sweep Level value when doing a Measurement is very similar to my question, and your original solution of leaving those levels at their default values and adjusting your AVR volume until the SPL reads 75 dB is pretty much exactly what my solution has been. I'm currently thinking about @John Mulcahy 's answer to your question.

 

[sam_adams]

I still don't understand why REW's sweep level is at -12.0 dBFS by default, but that doesn't mean that I can't use that sweep level setting, and accomodate it by changing my MiniDSP's input gain and my AVR's volume when I want to measure a speaker or a subwoofer.

From your question in the other discussion, I believe—and I'm sure @John Mulcahy will correct me if I'm wrong, which I won't mind in the least—that the -12 dBFS derives its level from the the SMPTE equivalent to 0 VU on a 16-bit scale. Zed Brookes had an interesting post from a while back on recording levels and bit depth that I've always kept in the back of my mind when working with REW.