Googling UMIK-1 pops up plenty of options, depending where you are the first one is sub EUR100. The second is about GBP 120.
I bought mine from Ideal AV, for £120, they have stock according to their website.
Mine came from a company called Kalibrate Ltd
The NDX2 USB port is only for storage devices, it cannot be used for USB Audio. You need another way to get the data into the NDX2
Sorry, the pic was a bit misleading.
I got stuck in the “measurement” tab.
It seemed as if i needed to pass a sound level check before it would allow the measurement to start.
I probably need to change the settings in “Preferences” so that it knows I’m using the ndx2 as a source, rather than the PC.
I’ll have another bash at it this afternoon.
REW doesn’t need to know about anything about your source.
You play your tones and set your level to typically 75dB (I use Pink Noise). Then you load the RTA, choose any options you need and then play your tones with the red “record” button pressed.
This is the RTA (real time analysis) window that you need to ‘listen’ to your tones/sweeps/pink noise. Change the smoothing dropdown to ‘Var Smoothing’ (Orange), the Record button is highlighted in Yellow.
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Not Guilty m’Lud.
I use a laptop with a USB to S/Pdif output external soundcard and send that to the 272.
(My laptop has 3 USB connectors)
If calibrating someone else’s system without an S/Pdif input I’ll use the laptop’s internal DtoA (reduced audio quality doesn’t matter too much so long as the frequency response is reasonably linear, the room will still have a much greater effect!).
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Thanks for the info, chaps.
Ordered 
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Excellent! Thanks for that.
I’ve had a quick mess around with REW using the advice you gave and feel ready to make a measurement.
I’ll have to wait until tomorrow, when the house is a bit quieter.
I’m sure that this will help a few people using the search function in the future.
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Here’s my first measurement.
This is my main L/R speakers (without Subs)
Recorded from the main listening position.
Doesn’t look great! 
Could you explain how you did the measurement with the Mic? There’s a guide on the Roon forum that covers the measuring quite well, which is where I got my information from. 
Are you speakers near a side wall?
Are they toed in cos it looks like you are off-axis?
Picture/thousand words.
Here’s how I went about it, step by step.
I’ve already got REW installed and have uploaded the UMIK calibration file.
First created a test tone. Pressed “Generator” icon.
“Noise” tab.
Select “Pink Random”
I ticked the box for custom and entered 10 hz for the Low Cut and 20000 hz for High Cut.
With hindsight, it would have been easier to select full range.
“Save to file” pressed the “WAV” icon in the bottom right.
I saved that file to a USB and put it in the front of my NDX2 and played it at low volume first, to check that it worked .
With the microphone in the listening position, I opened the “SPL Meter” and played the file from the USB, increasing the volume to about 75db.
I opened the “RTA” Tab, went to settings, changed “Smoothing” to Var Smoothing.
With the pink noise playing, I hit record.
I’ll hit the REW forums tonight and hopefully gain a better understanding for the subject.
@Slug
Thanks for the pic, I can see the mic position is wrong.
I’ll reply later with the process that I do as clearly as I can articulate.
Too kind. Thank you!
Hi @Slug,
Mine arrived today so I will certainly benefit from your experience. Indeed I already have: I was wondering how to get the file to the nDAC. I can see that I need to read the user manual…….all 317 pages of it ROFL
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There’s way too much info to absorb in everything that I’ve read elsewhere.
Guinnless very kindly broke it down to my level (Monkey see, Monkey do)
Don’t worry, I have every intention of asking all the questions that other people don’t want to, for fear of looking stupid! Haha!
That would be much appreciated. 
Looking forward to this as well. I bought the mic a few months and haven’t taken it out the box yet.
It looked a bit too complicated but mic was a bargain 
CK
Just been listening to T-Model Ford and Tom Waits 
This information has come from Magnus off the Roon forum and so I’m just re-providing it as I understand it in the simplest terms. Links aren’t allowed here but searching on the Roon forum for “A guide how to do room correction” should find it. 
I’ll break it down into sections and update as I go along.
This is what I do:
Three Pink Noise files are needed, one for both channels and the two others for individual left and right channels as below.
Fullrange, Pink Periodic, Sequence length 64k (this is how long you need it to play for during the measurements). The above screenshot does both channels (see bottom right), change to L or R as required. Use the Save to File button to save them to a USB stick to put in the streamer or nDAC. At this point you can play the files to make sure you have Both, Left and Right.
Plug the microphone in, REW should detect it and request the calibration file. The non 90 degree one is the one to use. Pop the foam on the end of the Mic.
Use the Both channels WAV file to set the volume to 75dB with the SPL meter set as below.
…
Next load the RTA window with the below settings. Click the ‘cog’ icon and select the Smoothing type as ‘Var Smoothing’. This takes the rough edges off the graph and makes it a bit easier to read. Note the Record button (square with red blob in the centre) on the top right of the chart.
Next we take some measurements. The microphone measurements should be taken in the following way - with the mic next to your ear corresponding to the channel that you are measuring move the mic in a spiral motion with some forwards and backwards motion too. If this all sounds a bit random that that is the aim so that and correction is not based with your head in a fixed position.
It’s important that you start recording only after you play the Pink Noise (PN) and stop the recording before you stop the pink noise. The RTA screen shows the number of averages - I use continue recording until I have a least 50 averages, more is also fine if the PN will play long enough!
Once complete if your measurement graph is out of the window use the ‘set graph axis’ button which is leftmost of the ‘cog’, click the ‘fit to data’ button which should straighten things out nicely.
In summary:
a) mic near your ear
b) start PN
c) start recording
d) move the mic and keep moving it
e) once you have 50+ averages stop recording
fI the PN runs out before you have 50+ readings change the sequence length in the Generator view. Save your measurement by clicking the ‘Save Current’ button.
To do the next channel you must reset the averages, click the ‘Reset Averaging’ button.
Repeat for the other channel!
I always start with the left channel but it doesn’t matter which one you do first.
Any questions, please ask
I’ll cover EQ next if all the above is correct. 
…
Select your chosen RTA channel from the Main Menu.
left-hand pane.
Next load up the EQ Window, click the Cog icon and set as per the dialog box below. Smoothing is again ‘Var Smoothing’.
In the right-hand pane of the EQ view set the Equaliser Type to be ‘Generic’, Target Settings as shown below. Use 75db as the Target Level - the same as the volume calibration.
Stay with the EQ view. These are the filter settings that I use - I don’t want any correction above 100Hz so the Match Range is set to 20 - 100Hz.
Nor do I want any boost, only cuts so the boost settings are all zero - adjust these if you need some boost but don’t try to fill plummeting troughs as these are usually cancellations and will never fill.
All other settings as as per the below screenshot.
Once you are happy click “Match Response to Target”, you may get a warning message if your target is a long way out but just click OK/Continue.
REW will then create the required correction and you’ll see the EQ filters
Repeat for your other channel.
At this point save all measurements from the File Menu, use a different file name from the RTA so you can always return to a clean sheet.
Awesome! I like the idea of moving the mic around for the averages.
I’ll have my homework done by this time tomorrow.
Thanks again 
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The only things that I had to stop and think about were -
-
The PN (pink noise) file only plays for about a couple of seconds, so I played it on loop in the NDX2
-
I also stumbled with the RTA settings. I was following your wording which mentions the smoothing settings.
I soon realised, looking at your picture, that the rest of the settings needed changing to match your’s too.
After doing the measurements for the main L/R speakers, I saved the file by pressing the icon “Both” at the top of the screen.
This auto saves to a folder within REW.
This is what I have so far.
(haven’t done L and R on their own yet. Just want to be sure that this is correct first)