This app note shows you how to set up the UMIK-1 and Room EQ Wizard (REW) on the Mac, together with an HDMI output device such as an A/V receiver or A/V preamp. This enables you to select individual output channels for use in measuring and equalizing a home theater or multi-channel surround system. You can use a Mac with an HDMI output port or a Thunderbolt port.

Your HDMI device will typically be an A/V receiver, but you may also have an A/V preamp or a Blu-ray player with HDMI input.

Please note: this app note requires OSX version 10.7.3 or higher. If you have OSX 10.6 or earlier and cannot upgrade, please try the "LineIn workaround," documented here.

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. 7000343.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.

2. Download and install software [Top]

You will need to download and install two items of software:

  • Download Room EQ Wizard (REW) from Home Theater Shack. You should get the latest version from the download area. This app note was tested with 5.01 beta 22.

  • SoundFlower is the application that we will use to "route" audio coming out of Room EQ Wizard to the various HDMI channels. You can download it from or directly from the Google Code download page. Please be sure to get the latest version, which as of the time of writing is 1.6.6b.

3. 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. Connect the UMIK-1 to your Mac using the supplied USB cable.

Connect your Mac to a suitable HDMI input of your A/V receiver or preamp. If using a Mac with an HDMI output port, you can use a regular HDMI cable. If using a Mac with a Thunderbolt port, you can use a Mini DisplayPort to HDMI adapter cable. Check that your HDMI device is set for multichannel output e.g. 5.1 or 7.1, and not to a stereo downmix.

The photograph below shows the necessary connections made to a Retina MacBook Pro.

UMIK-1 connection

4. Configure software [Top]

4.1. Audio MIDI Setup

Double-click on the Audio MIDI Setup app (in Applications/Utilities) to run it. Select the HDMI device, and:

  1. Select 48000.0 Hz in the Format drop-down selector.
  2. Click on the Configure Speakers... button. Set the HDMI device to the appropriate multichannel setting (e.g. 5.1 or 7.1 Surround), then click Done.
HDMI Multichannel speaker configuration

4.2. SoundFlowerBed

Double-click on the SoundFlowerBed app (in Applications/SoundFlower) to run it. This will show up as a little flower icon in the menu bar. Then:

  1. Pop the menu down and in the section Soundflower (64ch), select the HDMI device (see screenshot below).
  2. In the channel selectors, set the Channel 1 routing selector to HDMI [1] as shown below.
  3. Set Channel 2 to None - this ensures that REW will output audio to only one channel at a time.
Soundflower output channel selection for HDMI

4.3. Room EQ Wizard

Double-click on the REW app to run it. You will see a screen asking if you want to use the UMIK-1. Click on Yes.

UMIK-1 detected

Answer Yes to the next question about the calibration file, and then locate the file that you saved in Step 1 above.

Use cal file?

The main functions of REW will now be accessible from a row of buttons at the top of the window. This screenshot highlights the functions we will use in this app note:

REW buttons

Click on the Preferences pane, then:

  1. Check that the sample rate is 48 kHz.
  2. Set the output device to Soundflower (64ch).
  3. Verify that the input device has been set to the UMIK-1.
REW Preferences

5. Test and measure [Top]

Before proceeding, turn down the volume on your A/V preamp or receiver.

You can use the REW Signal generator to test that all is working correctly. Click on the Generator button and set the signal generator to "Speaker Cal" pink noise and the level at -12 dB, as shown in the screenshot below. Press the green play button. Gradually increase the volume on your A/V preamp or receiver - you should hear sound coming from the front left speaker.

REW Signal Generator

To check all channels, change the Channel 1 routing selector in SoundFlowerBed to HDMI [2], HDMI [3], and so on. (Remember to keep Channel 2 set to None. There is no need to make or change any settings for Channel 3 and upwards, as REW does not output to those channels.) Here is a typical mapping of channel numbers:

  • HDMI [1]: Front Left
  • HDMI [2]: Front Right
  • HDMI [3]: Center
  • HDMI [4]: Subwoofer
  • HDMI [5]: Surround Left
  • HDMI [6]: Surround Right
  • HDMI [7]: Surround Back Left
  • HDMI [8]: Surround Back Right

Open the REW SPL Meter, and click on the red button to turn it on. Increase the volume in your A/V receiver or preamp until the level reads about 75 dB.


You are now all set to run a measurement sweep. Select the HDMI [1] output channel again and click on the Measure button. Then use Check Levels and then Start Measuring. You will hear a sweep through the front left speaker, and REW will display its first frequency response graph. Then user SoundFlowerBed to select the next channel and run a measurement on it, and so on.

The UMIK-1, like all measurement microphones, is slightly directional and at high frequencies (6 kHz and above) is slightly less sensitive to the sides. For highest accuracy and repeatability, point the UMIK-1 at each speaker being measured. Alternatively, orient the UMIK-1 vertically (pointed at the floor or ceiling) and use a 90-degree calibration file such as that is supplied when the UMIK-1 is purchased via Cross-Spectrum Labs

After completing all channel measurements, you can view them together in the Overlays window. (Apply some smoothing to the graphs using the pop-down Controls overlay.)

Measurements mode over HDMI

What's next? [Top] [Top]

Now that you have the ability to run acoustic measurements, you can proceed to optimize and equalize your system. The following app notes contain information that you may find helpful in your journey:


The use of Soundflower for HDMI output routing was first documented by EmagSamurai.


Related Products - Acoustic measurement