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Problem with calibrating Preamp/audio card in REW
Old 10th November 2019
  #1
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Problem with calibrating Preamp/audio card in REW

Hello gearslutz,

before measuring my room with my Sonarworks XRef 20 mic and REW (the mic only contains a trial verison of Sonarworks Reference 4, this is why I want to get warm with REW) I want to make a calibration measurement of my preamp/audio card to subtract any coloration of these devices for future measurements.
At this point I am having a bit of trouble.

The measurement does not look like the ones I have seen it in many, many tutorial videos and articles approaching the 0 db line when using logarithmic scale. It is more approaching something above 2 db. Please have a look at the attachments.

Is this a simple misconfiguration of REWs views/scales or did I do something wrong regarding the setup?

The devices I am using are the RME hdsp 9632 as audiocard and the Focusrite OctoPre as preamp connected via ADAT to the hdsp. Since I will not connect the XRef 20 mic directly to the hdsp but with the OctoPre in between, it is not sufficient to simply connect the hdsp´s output to the input to make the calibration measurement, this would leave out the OctoPre. So I connected one hdsp´s analog output to one OctoPre input and the OctoPre´s output goes digitally via ADAT Toslink to the hdsp. Then I setup everything up in REW as shown in the attachments.
So is there any misconfiguration I am overlooking?

Best regards,
AudioTom2
Attached Thumbnails
Problem with calibrating Preamp/audio card in REW-img_6260-2.jpg   Problem with calibrating Preamp/audio card in REW-img_6259-2.jpg  
Old 10th November 2019
  #2
Lives for gear
 
akebrake's Avatar
 

Quote:
Originally Posted by AudioTom2 View Post
...Is this a simple misconfiguration of REWs views/scales or did I do something wrong regarding the setup?...
It certainly looks a bit strange. For a start you are looking at Linear frequency scaling. Just click the "Frequency Axis" box above the plot.


Upload a measurement here mdat (including soundcard measurement and mic cal file) and we can take a closer look.

As soon as one have a more "complicated" set up with a number of different digital boxes there is always a possibility that something goes wrong.
Like clocking errors, wrong sample rate etc etc

Best
Old 10th November 2019
  #3
Here for the gear
Quote:
Originally Posted by akebrake View Post
It certainly looks a bit strange. For a start you are looking at Linear frequency scaling. Just click the "Frequency Axis" box above the plot.


Upload a measurement here mdat (including soundcard measurement and mic cal file) and we can take a closer look.

As soon as one have a more "complicated" set up with a number of different digital boxes there is always a possibility that something goes wrong.
Like clocking errors, wrong sample rate etc etc

Best
Thank you for your response. Your hint about “linear frequency scaling” immediately let me find the problem!
I had the “Air”-switch of the OctoPre channel activated and didn’t realize it because of the linear frequency scaling which kind of hides the very strange frequency response of the air mode activated channel. It’s quite interesting how the air mode changes the behaviour of the channel. A comparison of deactivated (first photo) and activated can be found in the atrachment.
Due to test reports about the OctoPre the “airless” mode sounds rather heavy in bass, which makes this channel mode to a bass expert whereas the air mode is claimed to be more the allrounder. That surprises me considering the fact that the “bass expert” mode has a linear frequency response what I would generally rather consider as a channel mode suitable for most purposes, in other words an “allrounder”.
Attached Thumbnails
Problem with calibrating Preamp/audio card in REW-be471109-dac1-473a-820f-5abdc3f118f4.jpg   Problem with calibrating Preamp/audio card in REW-87b7e08d-20d4-488c-b950-d15dde4a6c66.jpg  
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