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Guenter Villnow
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Guenter Villnow
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This app note shows you how to set up the miniDSP UMIK-1 or UMIK-2 and Room EQ Wizard (REW) on a Mac with an HDMI connection to an A/V receiver. This enables you to measure each channel of a home theater or multi-channel surround system.

The app note assumes that you have already downloaded REW from roomeqwizard.com and installed it. If you are using a UMIK-2, get the most recent beta version from avnirvana.com. (You will need to register a free account to download.) This will ensure that you get a version that supports the UMIK-2.

1. Get your calibration files [Top]

Go to the UMIK-1 or UMIK-2 page and enter your microphone's serial number. It is in the form xxx-yyyy and labeled on the microphone. Ensure that you download both the regular calibration file and the 90-degree calibration file.

The calibration file ensures that your microphone is as accurate as possible. Each microphone has two unique calibration files, which is why the serial number must be entered. The regular calibration file is used when the microphone is pointing at or between the speakers, and the 90-degree file is used when the microphone is pointed at the ceiling.

2. Get connected [Top]

Figure 1 illustrates a typical measurement setup. The Mac is connected to an HDMI input of the AVR, although other devices with HDMI input such as a Blu-ray player or soundbar can also be used.

HDMI measurement with UMIK

Figure 1. Typical measurement setup

Mount the UMIK into a microphone stand. For home theater applications, it's usually best to point the microphone at the ceiling and use the 90-degree calibration file. Connect the UMIK to your Mac — see UMIK-1 setup with REW for examples.

If your Mac has an HDMI port, use an HDMI cable to connect it to your AVR:

HDMI connection from Mac for REW measurement

If your Mac only has USB-C ports, use a USB-C to HDMI adapter with an HDMI cable:

HDMI connection from Mac with USB-C hub for REW measurement

Dedicated USB-C to HDMI cables are also available, but are more limited in length.

Check that your receiver is set for multichannel output e.g. 5.1 or 7.1, and not to a stereo downmix.

3. Set sample rates [Top]

Set the input and output devices to the sample rate that you want to use.

  • If you are using a UMIK-1, set the output device to 48 kHz. (The UMIK-1 can only be set to 48 kHz.)

  • If you are using a UMIK-2, set both the UMIK-2 and the output device to the sample rate that you want to use, between 44.1 and 192 kHz.

Open the Audio MIDI Setup application. Click on the HDMI device and drop down the menu to set its sample rate. (Note that the AVR may not show up by its expected name — in our screenshots it shows up as "Panasonic TV" even though the Mac is connected to our AVR. This is due to EDID.)

HDMI device sample rate setting in Audio MIDI Setup

If you are using a UMIK-2, click on it and drop down the menu to set its sample rate. (The UMIK-1 can only operate at 48 kHz.)

UMIK-2 sample rate setting in Audio MIDI Setup

4. Configure[Top]

Double-click on the REW app to run it. You will see a screen asking if you want to use the UMIK-1 or UMIK-2. Click Yes.

UMIK-2 detected

Answer Yes to the next question about the calibration file:

Use
cal file for UMIK-2?

Use the dialog box that appears next to locate your 90-degree calibration file. (This assumes that you have pointed the microphone towards the ceiling.)

Select UMIK-2 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 button:

REW Preferences for HDMI and UMIK-2

  1. Set the sample rate to the rate you previously set in Audio MIDI Setup. The example shows 48 kHz.

  2. Set Output Device to the HDMI output device and set Output to Speaker.

  3. Verify that Input Device has been set to the UMIK-1 or UMIK-2. Set Input to MICROPHONE. It doesn't matter which channel you select, as they both have the same data.

5. Test [Top]

You will want to set your system to generate a suitable signal level. Before proceeding, turn down the volume on your A/V receiver.

Click on the Generator button and set the parameters as shown below. -20 dB is a good starting point for the level.

REW Signal Generator

Position your microphone at the listening position and turn the volume of your system down. Then click on the Play button (green triangle) and turn the volume up until the test signal is at a comfortable level.

Now open the REW SPL Meter. Click on the red button in the lower right corner to turn it on and adjust your system volume until the meter reads about 75 dB. Alternatively, change the output level in the REW signal generator. Close the SPL Meter window when done.

REW SPL Meter

Press the Play button again to stop the signal generator. Change the channel selector to Right and press Play again. You should hear sound from the right speaker.

REW SPL Meter HDMI channel select

Continue through the remaining channels to check that they all work as expected. If audio comes from the wrong channel, go back to the Preferences window and click on the Set Output Channel Mapping button, and re-assign channels as needed:

REW HDMI channel mapping

6. Measure [Top]

You are now all set to run a measurement sweep. Click on the Measure button:

REW measurement window with HDMI and UMIK-2

  1. Check the start and end frequencies. In this example, we set the range from 20 Hz to 20 kHz.
  2. Check that the level is set to the same value as you set it in the Generator window above.
  3. Check that the channel selector is set to Left.
  4. Click Check Levels.
  5. Click Start.

You will hear a sweep through the front left speaker, and REW will display its first frequency response graph. Repeat for all channels by clicking on the Measure button and changing the channel selector each time to Right, Center, and so on, to measure all channels.

HDMI channel selection for REW measurement

Change the name of each measurement as you go to keep track of which is which. 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. You can turn the display of individual graphs on and off with the checkboxes underneath. For example, here are the subwoofer and left speaker in our test system:

Example measurements mode over HDMI with UMIK

What's next? [Top]

Now that you have the ability to run acoustic measurements, you can proceed to optimize and equalize your system. Check out the acoustic measurements and home theater tuning app notes on our website. Have fun! Don't forget to let us know how you go in our forum.