The miniDSP UMIK-1 is the perfect companion to audio analysis programs running on your tablet or even your smartphone. In this application note we will show you how to set up your UMIK-1 for use with the AudioTools app from StudioSix Digital, running on an Apple iPad.
Please note: miniDSP cannot provide support for third-party applications or hardware. This app note shows you how to set up the miniDSP UMIK-1 to use with AudioTools but other functions of the Apple iPad hardware or the AudioTools app are beyond the scope of miniDSP support.
1. Get your calibration file [Top]
Go to the UMIK-1 page and enter your microphone's serial number. It is in the form xxx-yyyy and labeled on the microphone. Use "Save As" in your browser to save the numbers as a file e.g. UMIK-7001870.txt.
The calibration file ensures that your microphone is as accurate as possible. Each microphone has a unique calibration file, which is why the serial number must be entered.
"Sens Factor =-7.062dB, SERNO: 7001870" 10.054 -6.5726 10.179 -6.3949 10.306 -6.2205 ...
2. Get connected [Top]
Mount the UMIK-1 into the small stand supplied with it, or if you like, you can use any other microphone stand. To connect the UMIK-1 to your Apple iPad, you will need either the Lightning to USB adapter (for newer iPads with an 8-pin Lightning connector) or the Camera Connection Kit (for older iPads with a 30-pin connector). This photo shows an iPad mini connected to the UMIK-1 via the Lightning adapter:
To generate audio output from the iPad, connect a cable from the iPad headphone socket to the system being tested. On the iPad end, the cable will have a 3.5mm stereo jack, and typically the other end has a pair of RCA connectors, as shown at left in the photograph below. Alternatively, use a 3.5mm stereo to RCA adapter, as shown at right.
3. Calibrate [Top]
If you haven't already, install the Audio Tools program on your iPad from the App Store.
Open the app and go to the Settings men, and then select Microphone Setup. You will see see two choices: Low Range and High Range. Select Low Range.
Then click on the "i" icon to the right. This will bring up the microphone calibration screen.
In the screenshot above, the name of a UMIK-1 calibration file is shown. Initially, however, this will be blank, so you will need to load the calibration file to the iPad and select it. Click on the Calibration File link and then on the Files link at the bottom right. This will bring up a screen with information on how to transfer the calibration file from your computer to the iPad:
On your computer's browser, enter the address shown by AudioTools on the above screen and upload the calibration file from step 1 above. Then, back in the AudioTools interface on the iPad, tap on the name of the calibration file and tap Apply. The calibration screen will change to display the name, as shown above.
It is helpful to adjust the Trim parameter so that the SPL readings given by AudioTool are correct. Normally, you need a separate SPL meter to do this, but since each UMIK-1 contains a sensitivity calibration number (Sens Factor) in its calibration file, you can do this without one. Just work out the following formula:
Trim = 23 – (Sens Factor)
In our example cal file, the Sens Factor is given as -7.1, so the number we enter into the Trim field is:
Trim = 23 – (–7.1) = 23 + 7.1 = 30.1
(There is no need to use more than one decimal place for this calculation.) Then tap on Done to close the calibration screen, and on Done again to go back to the main AudioTools menu.
(Fortunately, you only need to go through the above procedure once!)
4. Measure! [Top]
AudioTools has a number of modules, some of which require additional "in app" purchase. Here, we will give a couple of quick examples of included modules. Click on the Acoustics icon at the left and then on the RTA icon. The display will show the spectrum of the signal being picked up by the UMIK-1. You can use this to monitor frequency content while music is playing:
The RTA can be changed between octave smoothing and 1/3rd octave smoothing using the selector at the lower left, and the decay time changed using the selector at the lower right.
To show more detail in the measured frequency response, use the FFT tool. This time, let's generate a pink noise signal so we can measure the frequency response of the system (rather than just the spectrum of music playing). First, open the FFT tool. then click on the small sine wave icon at the bottom of the screen. A control panel will pop up; set it for pink noise and tap the button at its top left. (Note: make sure to turn the iPad output volume or your system volume down first, and then increase it gradually.)
With pink noise playing through the system, the FFT shows the frequency response of the system as measured in the room. You can adjust the frequency resolution using the control at the lower left.