This app note will explain how to use the acoustic timing reference feature of Room EQ Wizard (REW) with a miniDSP UMIK-1 to accurately set delay between speakers in your home theater.
It assumes that you already have a working knowledge of measurements with REW. If not, first see the app note UMIK-1 setup with REW. REW version 5.15 or later is required.
- Setting things up
- Measure front left and right speakers
- Measure the remaining speakers
- Tabulate your results
- Update the configuration
- Wrapping Up
- Digging deeper
Since version 5.15, REW can be set to use an acoustic timing reference. Typically, you will use one of your existing speakers for this purpose. You can then measure the frequency response of any speaker (including the one being used for the timing reference) with time delay embedded in the measurement. This has two key uses:
If you export measurements to use in another program, that program can use the timing information to understand time (or phase) delays between the measurements. See the app note Multi-Sub Optimizer with UMIK-1 for an example.
If you need to set time delay in an output channel of a miniDSP processor in order to time-align different speakers, REW will show you the delay of the measured speaker relative to the timing reference. This is a common requirement in home theater. This app note will show you how to measure and set these delays accurately.
A typical setup is shown in this diagram:
In this example, we are using a nanoAVR HDA. You can also use nanoAVR HD with an A/V Receiver, or a 10x10 HD with analog connections. The measurement technique will still apply even if you are not using a miniDSP multi-channel processor but the measurement procedure is a bit less convenient.
As shown in the diagram above, the left front speaker is used as the acoustic timing reference – this is indicated by the red "wave" coming from it. Each speaker (including the left front) will be measured for its time delay relative to this timing reference.
Setting things up[Top]
First of all, disable bass management in the nanoAVR-BM plugin. The easiest way to do this may be to switch to an unused configuration i.e. one that is at the default settings. Or, if you are connecting your computer directly to an AVR for speaker timing measurement, disable bass management in your AVR (often accomplished by setting all speakers to "large".)
Start REW. If you haven't already, set up the UMIK-1 calibration. For multichannel sound system measurement, it it best to point the microphone at the ceiling and provide your 90 degree calibration file when REW asks for it. (You can download this file based on your microphone's serial number from the UMIK-1 page.)
Open the REW Preferences window and on the Analysis tab, under Impulse Response Calculation, select "Use acoustic timing reference" from the drop-down menu.
Measure front left and right speakers[Top]
Click on the "Measure" button (top left of the main window). Along with the other key settings (frequency sweep range and level), set both the output channel and the Timing Reference channel to "left", like this:
Now run a levels check and then the measurement sweep. You will hear a short "peep" from the left speaker, shortly followed by a full frequency range sweep. Rename the measurement to "Front Left".
Click on the "Measure" button again. This time, set the output channel to "Right" but leave the timing reference at "Left." You will use this setting for all remaining speakers. It looks like this:
Now run the measurement sweep and label it "Front Right."
Measure the remaining speakers[Top]
To measure the remaining speakers, the measurement signal needs to be routed to the other channels. The simplest way to do this is to use the Routing tab in the nanoAVR-BM plugin, which will be described below. Alternatively, you can use the method of routing to different HDMI channels described in our app notes Using the UMIK-1 and REW with HDMI output - Windows and Using the UMIK-1 and REW with HDMI output - Mac.
To measure the subwoofer, route input channel FR In to Sub Out, like this:
(The other rows don't matter, just FL In and FR In.) Now run a measurement sweep, leaving the output channel set to "Right" and the reference channel set to "Left," as set previously. Rename the measurement to "Subwoofer."
Repeat for the rest of the speakers. Here for example is the routing to measure the center speaker:
Tabulate your results[Top]
On the REW main window, click on the Front Left speaker measurement, and then click on the Info button:
Locate the parameter "System Delay" on the window that pops up, and write it down. For the front left speaker, it should be at or close to zero.
Other speakers will have a different delay. For example, this is our subwoofer:
Click on each of the other measurements and write down their value of System Delay. Here are the results from our test system:
Left front: 0.00 Right front: 0.02 Subwoofer: 2.69 Center: -0.27 Left Surround: -2.33 Right surround: -3.04
If the delay value is positive (right front and subwoofer in our example), it means that the speaker being measured is further away than the timing reference. If the value is negative (center and surrounds in our example), it means that the speaker being measured is closer than the timing reference. In our example, the microphone was very slightly closer to the left speaker than the right.
Update the configuration[Top]
Now we need to calculate the delay to apply to each speaker. Identify the speaker with the highest positive delay value. In our example, that is the subwoofer with 2.69 ms delay. Subtract each speaker's delay from that value and write it down. In our example:
Left front: 2.69 - 0.00 = 2.69 Right front: 2.69 - 0.02 = 2.69 (*) Subwoofer: 2.69 - 2.69 = 0.00 Center: 2.69 - -0.27 = 2.96 Left Surround: 2.69 - -2.33 = 5.29 Right surround: 2.69 - -3.04 = 5.73
(*) We are setting the same delay on front left and front right, as the slight difference is a measurement error.
Return to your regular configuration in the nanoAVR-BM plugin and set these delays in the output channels. Like this:
And that's it! You can now set up your bass management, based on accurate delays between all speakers. Don't forget to save your configuration to a file regularly.
Have fun, and please let us know how you go in our forum. If you want to learn a bit more about how this feature works, read on to the "Digging Deeper" section below.
What's going on here? We can gain a better understanding by viewing the impulse response of the speakers. Click on the Overlay button and then on the Impulse button above the plot:
Select the plots that you want to display and adjust the graph limits. You should see plots that look as in the following example. (If not, move the cursor onto the plot and select %FS from the drop-down menu. Adjust the time scale in seconds. Below, for example, we have set the scale from –0.003 to 0.003 seconds, or –3 to 3 ms.)
In the above screenshot, the left speaker's impulse response is shown in red. You can see that its largest peak is at 0 ms. This is where REW has determined the delay of the speaker relative to the timing reference to be.
The green plot shows the impulse response of the left surround speaker. We have placed the cursor at the location of its largest peak, which is –2.333 ms. That is, the left surround speaker is 2.333 ms "closer" to the microphone than the timing reference. This is the same (within margin of error and cursor placement) as the value that REW determined as the delay for this speaker.
Typically, the speaker being used as the timing reference has zero delay, but this is not always the case. The timing reference signal (the initial "peep") runs from 5 kHz to 20 kHz, whereas the measured response of the whole speaker runs over the full range. The impulse response of the full range measurement may be sufficiently different to the reference impulse response that the calculated delay is not zero, although it will be small. This is taken care of in the calculation method explained above.