# Adding Measurements to Measurement Groups

Once a measurement has been associated with a filter channel, it can be added to one or more *measurement groups*. A measurement group usually refers to a collection of measurements taken at a single listening position, but this need not be necessarily true for more advanced applications. More generally, a measurement group is a collection of measurements whose complex summation should ideally have a flat magnitude response vs. frequency (or conform to a house curve) as a goal for optimization. MSO can optimize the frequency response of multiple measurement groups simultaneously. If the measurement groups correspond to listening positions, the optimization improves response flattness and seat-to-seat variation of responses.

Assume we're using the example list of measurement names from the previous section, and repeated below.

MLP:Mains

MLP:Sub 1

MLP:Sub 2

MLP:Sub 3

MLP:Sub 4

Pos 2:Mains

Pos 2:Sub 1

Pos 2:Sub 2

Pos 2:Sub 3

Pos 2:Sub 4

Pos 3:Mains

Pos 3:Sub 1

Pos 3:Sub 2

Pos 3:Sub 3

Pos 3:Sub 4

Pos 4:Mains

Pos 4:Sub 1

Pos 4:Sub 2

Pos 4:Sub 3

Pos 4:Sub 4

The complex summation of all MLP measurements should ideally have a flat frequency response, and the same holds true for Pos 2, Pos 3 and Pos 4. Thus all the MLP measurements should be in the same group, all the Pos 2 measurements in another group, and so on. Why not call measurement groups "listening positions" or something similar? The reason is that most of the time, measurement groups do correspond exactly with listening positions, but not always.

Consider a two-channel system with two main speakers and two subs used in stereo mode. In this scenario, one measurement group might contain left main and left sub data at the MLP. Another measurement group might contain right main and right sub data, also at the MLP. A third group might contain left main, left sub, right main and right sub data all taken together at the MLP. Thus you'd want the frequency response of the left channel alone, the right channel alone, and both channels playing together in mono to each be as flat as possible vs. frequency after optimization. This is admittedly an unusual case, but it is supported.

Using the list of measurement names above, we'd create four measurement groups, one for each listening position (MLP, Pos 2, Pos 3 and Pos 4). To do so, in the Config View, right-click on the Measurement Groups to Optimize category node under Optimization Parameters and choose and choose Add Measurement Group from the context menu. This will add a measurement group and automatically pop up a dialog box allowing the measurements for the group to be chosen. Check all the measurement names beginning in "MLP", then press the OK button to apply the selections. Select the tree node with the measurement group name, which was automatically generated as "Measurement Group 1" and rename it using the usual method (F2 key) to MLP. Repeat the procedure for the three other listening positions. When you're done, you'll have four measurement groups, one for each listening position, each containing five measurements. See the tutorial section on measurement groups for specifics.

With measurement groups defined as above, MSO is ready to perform an optimization. If we were to run the optimization, MSO would try to optimize the frequency responses at the MLP, Pos 2, Pos 3 and Pos 4 to be as flat as possible. But before doing so, let's take a look at how we can display some data using graphs.