Multi-Sub Optimizer Tutorial (page 14)

Getting Information About the DSP Filters

To find out what the filter responses look like, you'll create a graph to plot them. Since your results may be different from the results above, open the tutorial_2_prefab.msop in the Sample Projects sub-folder of the tutorial to ensure your results match the tutorial. Then, use File, Save As to save it as tutorial_2.msop, overwriting the tutorial_2.msop you created earlier.

Create a new graph, then in Data, Filter Channels in the Graph Properties dialog, check the checkboxes for all four subwoofer channels (but not the mains channel, which has no filters). Press Apply. In Format, General, change the graph title to Filter Responses vs. Frequency. Check the Show legend checkbox. In Format, Axes, disable autoscale for the left y axis and set its lower and upper limits to -65 and 5 respectively. Press Apply to make sure the axis values are correct, then press OK to close the dialog. Rename the graph from Graph 2 to Filter Responses. Rename the [Filt chan] Trace 1, [Filt chan] Trace 2, [Filt chan] Trace 3, and [Filt chan] Trace 4 traces to Sub Chan 1, Sub Chan 2, Sub Chan 3, and Sub Chan 4 respectively. The new graph should look as below.

Filter channel responses after optimization
Figure 32. Filter channel responses after optimization

Filter Reports

You could determine the filter parameter values by selecting each one and looking in the Properties window, but using the filter report feature is easier and quicker. To see the filter report, activate the Config View and right-click on the Config 1 icon just underneath the topmost Configurations icon. Select Show Filter Report from the context window. This will open up a tabbed text window with the information you'll need to enter into the software of your DSP. If there are many filters, such as in this project, this could get tedious.

Biquad Information

Some DSP vendors, such as miniDSP, support a special text format which allows you to copy and paste all the parameter values for an entire filter channel into the software to configure all the filters in that channel at once. MSO supports the miniDSP format, but you'll need to enable it in the application options. Select Tools, Application Options from the main menu. On the left side of the Application Options dialog, select Hardware and Filter Reports. Check the checkbox labeled Include biquad information in filter reports. This activates the Sample rate selection radio buttons and the Biquad limit combo box. Be sure to choose the sample rate and the number of biquads per channel used by the actual hardware. For the purposes of the tutorial, choose 48 kHz for the Sample rate and 6 for the Biquad limit. In the Config 1 filters text view containing the filter report, right-click and choose Refresh from the context menu. This will cause the filter report to be updated with the biquad information. Pressing Page Down a few times will take you to the part of the filter report containing the information about the biquads and other related information. The portion for Sub Channel 1 should look as below.

Sub Channel 1:
FL1: Parametric EQ (biquad1)
FL2: Parametric EQ (biquad2)
FL3: Parametric EQ (biquad3)
FL4: Parametric EQ (biquad4)
FL5: LPF Linkwitz-Riley 24 dB/oct (biquad5, biquad6)
biquad1,
b0=0.999289245870467,
b1=-1.997957246800862,
b2=0.998811046390038,
a1=1.997957246800862,
a2=-0.998100292260505,
biquad2,
b0=0.998818991406365,
b1=-1.996962910604257,
b2=0.998307607188862,
a1=1.996962910604257,
a2=-0.997126598595227,
biquad3,
b0=0.998746233369988,
b1=-1.996741429491683,
b2=0.998189334211126,
a1=1.996741429491683,
a2=-0.996935567581113,
biquad4,
b0=0.999748065657730,
b1=-1.998989646925358,
b2=0.999274155844187,
a1=1.998989646925358,
a2=-0.999022221501918,
biquad5,
b0=0.000095059903807,
b1=0.000190119807613,
b2=0.000095059903807,
a1=1.972233747669657,
a2=-0.972613987284884,
biquad6,
b0=0.000095059903807,
b1=0.000190119807613,
b2=0.000095059903807,
a1=1.972233747669657,
a2=-0.972613987284884

You can highlight the text of a channel's biquad (biquad1-biquad6) and press Ctrl+C to copy it to the clipboard. You can then paste it into the miniDSP software to configure the appropriate biquad. See the miniDSP documentation for more information. Inexplicably, miniDSP has designed their software so that only a single biquad can be copied at a time in this way. However, you can save all the biquads of a given channel as a text file using MSO, and import the text file into the miniDSP software as an REW file. To export the biquad text 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. Right-click this node and choose Save Biquad Text for this Channel to save the channel's biquad text. Now you can import the entire channel's biquads into the miniDSP software to configure the whole channel at once. See the miniDSP documentation for how to do this.