Soundcard calibration curve changes depending on input volume/output volume combo

[FordTheWin]

Hi,

I am very new to REW but have done some searches online (no clear answers)

Equipment:
- Behringer ECM8000 mic
- Focusrite Scarlett Solo 3rd Gen

I have run a soundcard calibration but:
When using a higher input volume on the audio interface with a lower output volume I get more headroom (8.9dB), but a frequency response that's much more curved:

When using a lower input volume on the audio interface with a higher output volume I get less headroom (6.9dB). but a much flatter frequency response:

With a bit more tweaking of the input/output volume on the audio interface somewhere between the above two combinations, I then managed 8.5dB headroom, and the following curve:

So, this all has me quite confused and I'm not sure why this occurs or if any of the calibration files generated will be better or worse for future measurements.
Please help.
Thank you for your time and I appreciate any advice given,

 

[John Mulcahy]

Interesting to see the variation, but take note of the scale of the plots used for soundcard calibrations. The whole span is only +/- 3 dB, so the variations are actually quite small. There is no sign of any monitoring being active, which is good. For measurements made with the mic you can ignore the calibration, the mic itself will have much larger variations and the input gain will need to be adjusted to suit the mic and measuring distance anyway.

 

[FordTheWin]

Interesting to see the variation, but take note of the scale of the plots used for soundcard calibrations. The whole span is only +/- 3 dB, so the variations are actually quite small. There is no sign of any monitoring being active, which is good. For measurements made with the mic you can ignore the calibration, the mic itself will have much larger variations and the input gain will need to be adjusted to suit the mic and measuring distance anyway.

Thank you so much John, I spent hours looking over this and almost decided to send my audio interface back for a refund but you have put my mind at ease, cheers, your help is really appreciated.
Now I've just got to wait for my spl meter to arrive so I can callibrate the sound level.

 

[marcus aurelius]

Hi,

I am very new to REW but have done some searches online (no clear answers)

Equipment:
- Behringer ECM8000 mic
- Focusrite Scarlett Solo 3rd Gen

I have run a soundcard calibration but:
When using a higher input volume on the audio interface with a lower output volume I get more headroom (8.9dB), but a frequency response that's much more curved:

This is a little late but ... thought I would post it anyhow, as I had a similar experience - the sound card calibration changing with input level. As J Mulcahy pointed out in another thread, it's important to make direct routing through the sound card, and not to mix the test signal with the measurement signal.

This can happen inadvertently, if you use a Focusrite preset which uses so-called "custom mix" output routing. Frankly, I had not done much with my Focusrite, except to dabble with Ableton Live Lite. That all worked, so I never spent time to really understand the details of my Scarlett 4i4 gen 3 device. The factory default preset uses "custom mix" on the Monitor (Line) outputs 1-2, and the Line Outputs (3-4) ... this is bad for use with REW!

(BTW, this is what happens when you don't read the manual ... )

After spending some time to understand both the Scarlett and REW, I wrote up what I learned. Attached is a writeup describing how to set up the Focusrite Scarlett, and REW, to get a good sound card cal. Here is my result, using 48Khz sampling:

And this response is essentially constant, even if run 10-12 dB lower ...

Hope this helps others! Just trying to give back,