Getting Started With MSO

What You Need to Know Before Starting

Before using MSO, you'll need to have some experience with room acoustic measurement of subwoofers using the Room EQ Wizard (REW) software. If you're using a USB microphone like most do, REW is the only software recommended for taking measurements to be used with MSO. This is due to its acoustic timing reference feature that makes time-synchronized measurements with USB microphones possible.

If you're using an XLR microphone, it's possible to use other measurement software that can make use of a hardware loopback connection for time-synchronized measurements. Time-synchronized measurements are essential for the usage of MSO, because MSO uses the Superposition Principle in its calculations.

Before taking your measurements for MSO, you should perform the following test. This test demonstrates the Superposition Principle in action. You must use the same acoustic timing reference for all measurements.

• Set up your subs with your DSP so that you can energize the subs individually or together.
• Using the acoustic timing reference, measure one sub by itself at the main listening position (MLP).
• Do the same for a second sub by itself at the MLP.
• Measure both of the subs together at the MLP.
• Using the REW "A + B" trace arithmetic function, display the sum of the individual sub measurements taken above. The result should be nearly identical to the measurement of both subs taken together.

If these measurements don't add up correctly, there's probably a problem with the acoustic timing reference, such as forgetting to enable the timing reference or using different timing references for different measurements. This problem needs to be fixed and verified using the procedure above before taking your measurements to be used for import into MSO.

Some Key Concepts of MSO

In the descriptions below, it's assumed that measurements of only subwoofers and not main speakers are being considered. Although projects making use of both subwoofers and main speakers are supported by MSO, they aren't used often.

MSO requires a measurement for each sub at each listening position. If you have N_subs subs and N_pos listening positions, you'll need to take N_subs * N_pos measurements. For example, with 4 subs and 3 listening position, 12 measurements need to be taken.

Measurement, Sub and Listening Position Names

• After performing the measurements in REW, you export them as text, using file names that contain information identifying the sub that was measured and the position at which it was measured.
• These measurements are then imported into MSO using the Measurement Import Wizard.
• MSO gives each imported measurement a measurement name that's the same as the file name of the measurement, with all directory path information stripped off.
• After the Measurement Import Wizard completes, the Configuration Wizard is launched.
• In the Configuration Wizard, you specify information that includes:
  • The number of subs N_subs measured
  • The number of listening positions N_pos measured
  • A list of names for the N_subs subs
  • A list of names for the N_pos listening positions
  • For each combination of listening position name and sub name, MSO needs to know the name of the matching measurement.

Configurations

Once it has the information it needs about subs, listening positions and measurements, along with the association of each measurement to a specific sub and listening position, MSO only needs some additional bookkeeping information to be able to create a configuration. This additional information includes optimization options and the number and types of DSP filters you wish to use for each sub.

A configuration can be thought of in several ways. First, it is an object that groups the above data and options together and allows MSO to predict and optimize the performance of the system with the given data and options. Second, it can be thought of as enabling an experiment you can perform based on a set of options. Third, it gathers information needed to describe the DSP setup, including the various filter types and their parameter values to be used, how many channels are used, and so on. By creating multiple configurations with different options, you can run optimizations on each one to see which configuration best meets your goals.

Configuration Templates

After you create your first configuration, creating additional configurations is easier and quicker than the first one. That's because when the Configuration Wizard creates its first configuration, it also creates a configuration template behind the scenes. A configuration template is like a snapshot of the data gathered by the first run of the Configuration Wizard, but it only includes the data that doesn't change from one configuration to the next. That data consists mostly of the sub, listening position and measurement names and their relationship to one another. On the second and later runs of the Configuration Wizard, MSO detects that a configuration template is available, fills in most of the data for you, and takes you straight to the optimization options. This bypasses most of the data entry you needed to do on the first Configuration Wizard run. We'll see that in action shortly.

Identifying the Measurement for Each Listening Position and Sub

In versions of MSO prior to v2, you needed to manually match each measurement with a combination of listening position and sub. If you had a lot of subs and listening positions, that became cumbersome. By request, MSO v2 adds an algorithm that does this automatically for you if it can. Since you can pick any names you want for the measurements, subs and listening positions, the algorithm isn't guaranteed to work in all possible cases. By taking certain precautions in the naming of measurements, subs and listening positions, you can ensure that the algorithm will almost always succeed.

We'll discuss these precautions in the next section, then walk through creating a configuration with the Configuration Wizard to see how it all works in practice.