Compression/linearity measurements in offline mode

[moij]

How to measure compression (actually input level vs. output level linearity) with REW and mic and in offline mode?
Stepped sine measurement on RTA works only in online mode, signal cannot be saved to file and used in offline mode.

 

[John Mulcahy]

There isn't a way to do that in REW.

 

[moij]

Can this function be added to request list?

 

[John Mulcahy]

It wouldn't be practical using a stepped sine approach, each signal would need a synchronisation tone and the whole procedure would be pretty tedious. A more practical approach would perhaps be an adaptation of the "Level sweep" approach (Fast distortion measurements in relation to frequency and level) though that has limitations at levels approaching full scale. I don't have any plans for that, however. If you were to create a test signal with a tone that ramped in level, capture that after playback through the system, import the capture as audio data and then look at a slice through the spectrogram of the import that would give a similar result for the level. Alternatively make a series of offline sweep measurements at different levels and examine the behaviour over the sweep responses at the frequencies of interest.

 

[moij]

This seems little difficult and time consuming to implement with current functions existing in REW.

I have one more related request.
REW is missing function to display stepped sine measurements on Overlays.

 

[John Mulcahy]

I guess you mean stepped in level? You can display stepped level sine measurements on the distortion overlay.

 

[moij]

Yes, I mean stepped level sine measurements, but there can be displayed only THD, not Input vs.output level lines and Linearity lines.

 

[John Mulcahy]

I have added Level and Linearity overlays in the next beta build.

 

[moij]

This is great.