Measure from Externally Generated Signal?

[squasher]

Is there anyway that REW can measure the SPL/frequency response for an externally generated signal? i.e. REW is not the Signal Generator..

I am using REW to determine the Frequency response of my Reel-to-Reel playback amplifier and try to adjust the HF / LF Equalization to get a flat response. I would like to be able to play a slow frequency tape (from 20 Hz to 20 kHz) on my machine and get REW to display the corresponding response for the output of the Reel-to-Reel machine.

The tape does not have a timing reference that I am aware of.

 

[dcibel]

No timing reference needed for basic FR.

I would use the RTA window, set to spectrum mode and use the peak response.

 

[squasher]

Thanks for the suggestion. Unfortunately, I tried that and all the harmonics that are captured tend to overwhelm the analysis of the fundamental frequency that I'm trying to adjust for.

What I'm looking for is something that looks like the following image:

 

[dcibel]

Yeah, fair enough, I tested with loopback signal gen and I see what you mean. Not harmonics, it would be silly if harmonics were higher amplitude than the fundamental, but rather the length of sweep vs FFT time for the RTA, requires short FFT length for the fastest result, and then a very long sweep time, else there is "gaps" in the response. A recording of white noise would seem to be a better solution for the RTA than using a sine sweep.

 

[John Mulcahy]

You can do it, the trick is to use an FFT that lasts longer than the sweep being measured. Here is an example capturing a 10 second sweep with a 1M FFT. Wait for the FFT to do one full update (i.e. draw a noise floor response on the graph) before starting the sweep.

 

[dcibel]

You can do it, the trick is to use an FFT that lasts longer than the sweep being measured.

D'oh, of course. My brain sure isn't working well today.