Multi-Sub Optimizer Reference Manual (page 13)

Gathering Filter Information: Filter Reports and Biquad Export

Once you've created multiple configurations, optimized them, and decided which one you're going to use, you'll need to gather the filter parameter information of the final configuration for entry into your DSP device by running a filter report. Devices from Behringer require that the filter parameters be entered one-by-one into the control software. For such hardware, you'll need to get the filter parameters from MSO's filter report. Devices from miniDSP allow for importing files containing all required filter information for all filters in a channel at once. MSO allows for generation of such files as explained below.

Supplying Information About Your AVR

Before running a filter report, you'll need to tell MSO some things about your AVR and DSP device so it can tailor the filter report to match the capabilities of your hardware. To do this, choose Tools, Application Options from the main menu, then click on Hardware to show the property page for specifying your hardware properties. This property page is shown below.

Telling MSO About Your Hardware
Telling MSO About Your Hardware

For more information about this property page, see the related tutorial topic.

Listing Filter Information in a Filter Report

At any time, you can see a summary of the parameter values of all filters in a configuration by choosing Config, then Show Filter Report from the main menu. This will list all parameter values for all filters of the chosen configuration in a tabbed text view. This can also be done by right-clicking on the root node of a configuration in the Config View and choosing Show Filter Report per the image below.

Showing the Filter Report
Showing the Filter Report

Contents of the Filter Report

A tabbed text view with filter information will appear as in the figure below.

Filter Report Display
Filter Report Display

The filter report data shows all parameters of all filters, grouped by filter channel to help with data entry into hardware such as the Behringer DSP amps. For these amps, you'll need to enter the data manually using the application they provide. For information about compatibility of Behringer DSP devices with MSO's filter types, see the Behringer compatibility section.

If you're using a miniDSP device, the filter information can be exported from MSO as a biquad text file for each channel. Then each biquad text file can be imported into the miniDSP. When you import this biquad text file into a miniDSP channel, it sets all the parameters of all the filters in that channel in one step.

Even if you're using biquad text export from MSO for import into a miniDSP device, you'll still need to enter MSO's calculated delay and gain values manually. This information is gathered at the end of the filter report. The quickest way to access it is to click in the filter report window, then press Ctrl+End. You'll see something like the text shown below.

Final gain and delay/distance settings:
Complete gain settings for chosen fixed SPL target level (optional):
No change to AVR sub out trim gain
Sub 1 gain: -0.30 dB
Sub 2 gain: -5.98 dB
Sub 3 gain: -5.58 dB
Sub 4 gain: -0.30 dB
Minimal gain settings, neglecting SPL target:
Sub 1 gain: -0.00 dB
Sub 2 gain: -5.68 dB
Sub 3 gain: -5.28 dB
Sub 4 gain: 0.00 dB
Delay settings:
Sub 1 delay: 17.17 msec
Sub 2 delay: 0.00 msec
Sub 3 delay: 16.60 msec
Sub 4 delay: 17.54 msec

Shown above is the information for a sub-only configuration. In this case, you should use the delay settings shown, and the Minimal gain settings, neglecting SPL target. For subs+mains configurations, the information is the same, except the Minimal gain settings, neglecting SPL target section is not present. An example is shown below.

Final gain and delay/distance settings:
Increase AVR sub out trim gain by 9.50 dB
Sub Channel 1 gain: -5.90 dB
Sub Channel 2 gain: -0.33 dB
Sub Channel 3 gain: -14.36 dB
Sub Channel 4 gain: -4.50 dB
Increase AVR sub out distance by 12.40 feet
Delay settings:
Sub Channel 1 delay: 12.35 msec
Sub Channel 2 delay: 4.54 msec
Sub Channel 3 delay: 4.47 msec
Sub Channel 4 delay: 0.05 msec

In this example, small gain tweaks are enabled in the miniDSP to make up for the 0.5 dB AVR sub gain adjustment resolution.

Using Biquad Support

MSO supports biquad parameters and biquad file export in miniDSP-compatible text format. To enable this support, go to the main menu and select Tools, Application Options. On the left side of the Application Options dialog, select Hardware and Filter Reports. This will cause the hardware options property page to be shown as below.

Enabling Biquad Support
Enabling Biquad Support

Check the Enable miniDSP-specific biquad reporting and file export checkbox. This activates the Sample rate selection radio buttons and other controls that allow you to set the input, output and crossover biquad limits. It's absolutely essential to select the correct sample rate here, or else the actual filters loaded into the miniDSP will be invalid. The miniDSP hardware and biquad properties are configured above for the miniDSP 2x4 HD. The miniDSP 2x4 HD uses a 96 kHz sample rate, while the 2x4 non-HD miniDSP units use 48 kHz. For compatibility with the miniDSP 2x4 HD device, enter a value of 10 for the input and output biquad limit as shown in the illustration above. The biquad limit for the non-HD miniDSP 2x4 devices depends on the software plugin used. Consult the miniDSP documentation for details. Once Enable miniDSP-specific biquad reporting and file export is checked, biquad file export will be enabled, and the biquad information will also be shown in the filter report.

Exporting Biquad Text

To export the biquad text of a filter channel as a file, go to the Config View and navigate to the filter channel whose biquads you want to save as text. Select the Filters folder node of the channel whose data you wish to export. Right-click this node and choose Save miniDSP Biquad Text for this Channel to save the channel's biquad text. This is shown below.

Exporting the Biquad Text
Exporting the Biquad Text

Once the biquad text file is exported, you can import the entire channel's biquads into the miniDSP. Its software will configure all the filter parameters of all the filters in that channel at once. See the miniDSP app note titled "Auto EQ with Room EQ Wizard" for how to load the resulting biquad data file into the miniDSP. See also the information on miniDSP biquad text file export and import, as well as manual entry of miniDSP gain and delay parameters in the tutorial for more specifics.

Extending Filter Capacity by Using Crossover Biquads

The checkbox labeled Use crossover biquads if output biquad limit exceeded enables the MSO feature to extend the number of available biquads per channel. Saving biquad files when using this feature is done exactly the same way as described above for saving a conventional biquad file. However, if the number of biquads needed by a given MSO filter channel exceeds the miniDSP output channel biquad capacity, two biquad files will be saved. The second file, used for the crossover biquads, will be automatically generated and will have the same name as what you chose for the output biquad file, but with "_xo" appended to it before the extension. For instance, if the biquad count exceeds the output channel biquad capacity and you choose to save the output biquad file under the name "chan1.txt", a second file, named "chan1_xo.txt" will be automatically generated and will contain the biquads to be pasted into the crossover in the "Crossover advanced mode" of the miniDSP software.

MSO attempts to fill up the crossover biquads first, then uses the output biquads for the remainder of the biquads (if any). The reason for this behavior is that some of MSO's filter types require as many as four biquads to implement. It's possible that such a filter could be split up between the crossover and output biquads. If the output biquads were populated first, such a filter would be partly implemented on the output side of the output biquads and the input side of the crossover biquads. But the ordering of biquads within these more complex filters is optimized to prevent digital clipping. Splitting up a filter in this way would alter the biquad order within such filters, among other problems. By filling up the crossover biquads first, any filter that uses more than one biquad and that gets split between crossover and output biquads has some of its biquads at the output side of the crossover and the rest at the input side of the output biquads. This preserves the biquad order within these multi-biquad filters and also keeps the individual biquads of such filters contiguous in a signal-processing sense.

This property of filling up the crossover biquads first can cause unusual results in certain specific situations. Suppose you're using a miniDSP device with an output capacity of six biquads and a crossover capacity of eight biquads, and have a channel configuration in MSO with seven PEQs. These seven PEQs will require seven biquads. In this case, MSO will put all seven of them in the crossover biquads, padding the crossover to eight as required for the copy/paste in the miniDSP "Crossover advanced mode". When saving the biquad files and choosing, say, "chan1.txt" for the output biquad file name, two biquad files will be created: "chan1.txt" and "chan1_xo.txt". The "chan1_xo.txt" will contain all the data needed for implementing the seven biquads in the crossover, and the "chan1.txt" will not contain any biquad data at all, only a note saying that all the needed data are in "chan1_xo.txt". The file name you choose in the dialog for saving biquad files should always be the name of the output biquad file. The name and content of the crossover biquad file will be automatically generated if needed.

Exporting Biquads For Use With BEQ

BEQ is a collection of programs and a database used to equalize the bass of individual movies to compensate for premature bass rolloff imposed in the production process.

Its implementation makes use of the input filters of miniDSP devices. In MSO, it's also common to use shared sub filters, which are also implemented using the miniDSP input filters. If you wish to use shared sub filters in MSO, together with BEQ, this creates a conflict regarding miniDSP input filter usage. MSO resolves this conflict using the Save BEQ miniDSP Biquad Text for this Channel command in the Config View. This command can be seen in the figure above

This command works by making use of a filter equivalence relationship involving shared filters. Suppose you have a shared filter channel with filters FL1, FL2, FL3 and FL4. An exact equivalent circuit can be made by removing these filters from the shared (input) channel and replicating them all in each of the miniDSP output channels. Although somewhat wasteful of filters, one can make use of the biquads contained in the almost-never-used miniDSP crossover filters to implement them. By using the Use crossover biquads if output biquad limit exceeded option in the Application Options property sheet, together with the Save BEQ miniDSP Biquad Text for this Channel command, MSO will automatically do this filter equivance transformation for you, then automatically create the biquad text files to implement the filters using the crossover biquads if need be. This means that for the miniDSP 2x4 HD, the number of per-sub PEQs plus the number of shared PEQs that you use in MSO can be as high as eighteen, while still freeing up all ten input PEQ slots for use with BEQ.

This technique also completely eliminates the need for any biquad merging that may be provided by some of the BEQ software, as MSO won't use any input biquads for this case at all. In other words, all shared filters that would ordinarily end up in the miniDSP input biquads are removed, then replicated in each output channel, using the crossover biquads as needed. The price paid for this feature is the need to copy and paste the crossover biquad file contents (if any) into the miniDSP crossover instead of using the more convenient file import for the output biquads.

Saving Configurations in Equalizer APO Format

This feature is for two-channel systems using a Windows-based HTPC with multiple subwoofers. The custom signal routing feature of the Equalizer APO software can be used to implement the required bass management. It is the subject of a dedicated article.