Calibration and Measurement

[lorrain]

Hi
I notice a particularity in Soundcard Calibration/ Measurement in low frequencies with my soundcard.
I use this soundcard : Clarett2-pre-usb from Focusrite.
I connect only soundcard output 1 to soundcard input 1 and perform 3 measurements:

• Measurement with no calibration
• Calibration (Preference and Calibrate soundcard processus)
• Measurement with calibration

Under 10Hz, Measurement with no calibration (1) doesn’t not match with Calibration (2).
I tested all the possible settings with the same result.
I use REW 5.20 RC2 (windows10 64 bits)
I use others software (ARTA, AUDIOTESTER). REW Calibration is in concordance with all these softwares.
Calibration seems correct but not Measurement.
I don’t understand because the parameters in Calibration and Measurement are identical.
Attachements:
1/Capture : Measurement without calibration (red), Calibration (green), Measurement with calibration (blue)
2/Preferences
3/Make a measurement
It is not a problem for me but I would appreciate a lot to understand!

Thanks

 

[John Mulcahy]

Are you referring to the ripple at low frequencies? That will disappear if you increase the right hand IR window, the default measurement window of 500 ms may produce some truncation of the response if the interface has a very low cutoff frequency, which produces ripples in the response.

 

[lorrain]

Thank you very much John.
All is perfect now with a higher value of right hand IR window.

 

[lorrain]

I can modify the value and the curve become perfect but Is there a way to save the new value when closing the REW software?

 

[John Mulcahy]

The default window settings can be changed in the Analysis preferences.

 

[lorrain]

Excellent
Thank you very much