Multi-Sub Optimizer Tutorial (page 6)

The Two Ways of Specifying Filter Parameter Limits

It's important to understand that there are two methods used to specify filter parameter limits. These are:

If you want to change the parameters or parameter limits of an existing filter, you must use the Properties Window on the right side of the main window (Figure 9 below). To change a filter's parameters or parameter limits, you must first select it in the Config View. Once the filter is selected, its parameters and their limits will be displayed in the Properties Window where you can edit them.

When you modify a filter using the Properties Window, the changes you make are stored in the filter object itself and saved to the project file when you save the project. Using the Properties Window is the only way to modify filter parameter values.

The filter settings of the Application Options dialog of Figure 10 below change only the default filter parameter limits for newly-created filters. This dialog does not affect parameter limits of existing filters, nor can it be used to specify default filter parameter values. Using the Application Options dialog is useful when dealing with e.g. the Behringer iNuke DSP amplifiers. The Q parameter of the parametric EQ filters of the iNuke DSP amps is limited to a maximum value of 10 by the iNuke firmware. If you set this maximum Q value to 10 in the Application Options dialog, all subsequently-created PEQ filters will have Q limits compatible with the iNuke DSP amps. The Application Options dialog is less useful with miniDSP devices, as their use of biquad file import to specify filter parameter values imposes few constraints on parameter limits. However, you may still wish to use the Application Options dialog in connection with miniDSP devices if you want to allow boost in PEQ filters by default.

When you modify default filter parameter limits using the Application Options dialog, the changes are saved in the Windows registry and persist across projects.

Modifying Individual Filter Parameters and Limits Using the Properties Window

When a filter is selected in the Config View, the Properties Window on the right side of the main window will show information about the filter, its parameter values, and the upper and lower limits of permissible values of each parameter. This is illustrated below.

Properties Window
Figure 9. Properties Window

The first group of properties is Filter Information. You can't alter any of the Filter Information values as their purpose is just to identify the filter, its type, and other information about it. Below Filter Information are the parameters, their names, values, and the upper and lower limits of those values. Only the information in the right column can be changed. You can change the values themselves in the right column by editing them as you would in a spreadsheet. In addition, when you click in the right column of the Value field, a spin control with up and down arrows appears, allowing you to tune the value by pressing either of these two arrows.

The Optimization allowed field controls whether the optimizer is permitted to alter the value of the parameter. If set to False, the parameter will retain the value set in the Properties window and won't be changed by the optimizer.

Notice the Maximum value field of the Boost (dB) parameter has a value of 0 dB to disallow boosting. This is only an initial maximum value as a safety feature for some DSP hardware that might have dynamic range problems when boosting is done. You can manually edit the maximum value of the boost to be up to 15 dB, which is likely to be much more than you'd ever want to use. You can also set the default minimum and maximum values of newly-created filters of all types. You'll look at that next.

Using Application Options to Set Default Filter Parameter Limits

MSO is initially set up with default values for the minimum and maximum parameter limits. These limits prevent the optimizer from adjusting parameters to values that are either impractical or beyond the capability of your DSP hardware. You can change these limits using the Application Options dialog. From the main menu, choose Tools, Application Options. The Application Options dialog will be shown as below.

Application Options dialog
Figure 10. Application Options dialog

Assume the DSP being used has a maximum delay of 15 milliseconds. Check the Use custom value for minimum allowable delay checkbox and enter 0 into the Minimum delay, msec edit control. Check the Use custom value for maximum allowable delay checkbox and enter 15 into the Maximum delay, msec edit control. Now all newly-created delay blocks will have these limits for the delay. You can override the limits manually after the delay block is added, by using values as low as -60 milliseconds for the lower limit and as high as 60 milliseconds for the upper limit. A negative delay means that the delay should be reduced relative to the as-measured condition, which means increasing the sub distance in your AVR from what it was when the measurement was performed.

You can configure custom minimum and maximum values for each of the parameters of other filter types too, but for this tutorial you'll keep all of them at the default values except the minimum and maximum delays. These values will stay in effect for all projects, not just the current one. Changes you made to the default minimum and maximum delays affect only newly-created delay blocks.