Every measurement mic is slightly different. A calibration file tells REW exactly how your mic differs from perfect, so your graphs show the room rather than the mic.
Load your calibration file
Beginner
- Find your mic’s serial number on the mic body. For the UMIK-1 it’s seven digits in the form XXX-XXXX.
- Enter it on miniDSP’s UMIK-1 or UMIK-2 product page to download your files.
- You’ll get two files, for example 8100002.txt and 8100002_90deg.txt.
- Plug the mic in and open REW. When REW asks, say yes and choose the file that matches how the mic will point (see below).
- In Preferences, select your mic as the input and choose its MICROPHONE input, not Default Input. REW needs this to show correct sound levels.
- Leave the input volume at 0 dB. REW says a USB mic doesn’t need boosting.
0 degree or 90 degree?
| Mic points | Use | Best for |
|---|---|---|
| Straight up at the ceiling | The 90 degree file | Room and bass measurements, and multichannel systems |
| Straight at the speaker | The 0 degree file | Measuring one speaker, especially at high frequencies |
The file must match how the mic is pointing. For most room measurements, point it at the ceiling and use the 90 degree file, the same as for Dirac Live.
It’s the same file Dirac Live uses. See Step 2: Choose Your Microphone for the download walkthrough with screenshots.
Source: miniDSP’s product pages and REW’s help. Applies to the UMIK-1 and UMIK-2.
Calibration in more depth
Advanced
Sensitivity factor
The first line of a UMIK file contains a sensitivity figure. REW uses it, along with the mic’s known gain settings, to turn the mic’s digital level into real sound pressure level. That’s why you don’t need a separate sound level meter. REW knows how to do this for the UMIK-1, UMIK-2 and several other USB mics.
Users have reported that re-downloading a UMIK-1 file for the same serial number can give a different sensitivity figure, and a different SPL reading in REW. miniDSP says the readings should match. Keep a copy of the file you use, and re-check your levels if you ever swap files.
The 90 degree file is calculated
miniDSP measures each mic on-axis and calculates the 90 degree file from that measurement. It’s still the right file to use when the mic points upwards.
UMIK-2 differences
- It supports 44.1 to 192 kHz. REW may give wrong readings if REW’s sample rate doesn’t match the operating system’s, and 48 kHz is a safe choice.
- On Windows, miniDSP’s guidance on drivers varies between its product page and its manual. Their HDMI app note using FlexASIO covers both mics.
Soundcard calibration
REW’s soundcard calibration step isn’t needed with a USB mic. Skip straight to checking levels.