Multi-Sub Optimizer Reference Manual (page 25)

The Application Options Property Sheet (continued)

The various property pages in the Filter Parameter Defaults category of the Application Options property sheet will be discussed here. These property pages share a set of common characteristics, which will be discussed first. Then the unique characteristics of each page will be described.

The Common Traits of the Filter Parameter Defaults Property Pages

Usage of the Filter Parameter Defaults property pages is just one of several ways to set filter parameters. Filter parameters consist of both parameter limits and values. The limits represent the range over which the optimizer is allowed to adjust the parameter values during optimization.

The Filter Parameter Defaults property pages only affect the default values of the parameter limits. Furthermore, these parameter limits only apply to filters that have yet to be created, not existing filters. This creation can be done either indirectly from information on the Specify the Configuration Properties page of the Configuration Wizard, or directly by the user manually adding filters.

For a comprehensive description of all the different ways filter parameter values and their limits can be specified, see the topic in the "Tips and Tricks" section titled The Different Methods of Specifying Filter Parameter Values and Limits. That topic includes some details that aren't discussed here, but are nonetheless important aspects of the Filter Parameter Defaults property pages.

An example of a Filter Parameter Defaults property page is shown below.

The Filter Parameter Defaults Property Page for PEQs
The Filter Parameter Defaults Property Page for PEQs

If you wish to change the default parameter limits from the program defaults, check the corresponding Use custom value for... checkbox. This will enable the corresponding edit control, allowing you to change the chosen limit value. Each filter parameter has both a minimum and maximum limit value. The Parametric EQ filters have three parameters, giving a total of six adjustments, consisting of the minimum and maximum allowable value for each of its three parameters. These limit values are further constrained by some absolute limits that are not user-adjustable. The purpose of these non-user-adjustable absolute limits is to prevent extreme values from being assigned to any parameter limits.

The changes that you make in the Filter Parameter Defaults property pages are stored in the Windows registry, so they apply to all projects. If you use a project on multiple computers, be sure the filter parameter defaults that are important to you are set to the same values on all the machines you're using for MSO. For most users, this usually consists of the default parameter limits for gain blocks, delay blocks and parametric EQ filters. Most of the rest of the filter types supported by MSO are for unusual situations.

The Individual Filter Parameter Defaults Property Pages

The options for the default parameter limits of all filter types supported by MSO are described below.

The Delay Parameter Defaults Property Page

The Delay Parameter Defaults property page is pictured below.

The Delay Parameter Defaults Property Page
The Delay Parameter Defaults Property Page

Notice that the default minimum delay shows a negative value, which appears to make no sense. However, allowing negative delays is an important technique used by MSO to help it find the best final delay values or AVR sub distance setting. This is done as follows.

Because of these considerations, the minimum allowed delay should be negative, and should usually be set to the negative of the maximum allowed delay. Note that for the miniDSP 2x4 HD, the maximum delay allowed in the hardware is 80 msec, which way too large for practical applications. For this reason, it's suggested to keep the allowable delay range at the default of ±20 msec for the miniDSP 2x4 HD. This recommendation also applies to other DSP devices having extreme delay range adjustment.

The Gain Parameter Defaults Property Page

The image below shows the Gain Parameter Defaults property page.

The Gain Parameter Defaults Property Page
The Gain Parameter Defaults Property Page

As with delay blocks, there are two principal ways that gain blocks are created.

However, unlike delay blocks, the parameter value limits of gain blocks created by the Configuration Wizard are not affected by the limits you specify on this property page. That is because the Configuration Wizard uses a special arrangement of gain blocks to help guarantee optimization success in a variety of circumstances without burdening the user with peforming the needed calculations. This special gain block arrangement has the following characteristics.

Because of this behavior of the Configuration Wizard, the gain value limits specified here are only used for manually-created gain blocks.

Even though gain blocks created either manually or by the Configuration Wizard can have positive values for their maximum gain, the computations of the filter report final gain values adjust the gains in such a way that only a shared gain block can have a positive gain in dB. Individual sub gain blocks are adjusted to have either 0 dB gain or a gain in dB that's negative (that is, an attenuation).

The Parametric EQ Parameter Defaults Property Page

The Parametric EQ Parameter Defaults property page is shown below.

The Parametric EQ Parameter Defaults Property Page
The Parametric EQ Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following two filter types.

The PEQ parameter limits you can adjust are as below.

When you run the Configuration Wizard, it creates Parametric EQ filters automatically from information provided on the Specify the Configuration Properties wizard page. Unless you change these filters, they will have the parameter limits specified in this property page. Also, if you manually create PEQ filters, their parameter limit values will be as you specify here. Setting these parameter limits on this property page is advantageous for several reasons.

For parametric EQ filters, the limits set on this property sheet are not necessarily the final story. On the PEQ Parameter Limits property page of the Optimization Options property sheet, you can set all parameter value limits for all PEQs of a configuration at once, at any time. That behavior is in contrast to how the parameter limits specified in these Filter Parameter Defaults property pages work. These property pages only affect the parameter value limits for newly created filters. The parameter limits specified in the PEQ Parameter Limits property page of the Optimization Options property sheet can alter the filter parameter limits at any time after these filters have been created. Be sure to read the PEQ Parameter Limits property page documentation for complete information.

The LPF Parameter Defaults Property Page

The LPF Parameter Defaults property page is illustrated below.

The LPF Parameter Defaults Property Page
The LPF Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter types.

The LPF parameter limits you can adjust are as below.

For 6 dB/oct filters, as well as Butterworth filters of all order, the cutoff frequency is the -3 dB frequency. For Linkwitz-Riley filters of all order, the cutoff frequency is the -6 dB frequency. For Bessel filters, the attenuation at the cutoff frequency varies with order.

The LPF Variable Q Parameter Defaults Property Page

The LPF Variable Q Parameter Defaults property page is shown below.

The LPF Variable Q Parameter Defaults Property Page
The LPF Variable Q Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

This Variable Q 12 dB/oct LPF filter type allows you to implement several LPF types as special cases. These are as follows.

When a Butterworth 12 dB/oct filter (Q = 0.707) is implemented with this filter type, its cutoff frequency is the -3 dB frequency. When a Linkwitz-Riley 12 dB/oct filter (Q = 0.5) is implemented, its cutoff frequency is the -6 dB frequency. For other values of Q, the attenuation at the cutoff frequency varies.

The HPF Parameter Defaults Property Page

The HPF Parameter Defaults property page is illustrated below.

The HPF Parameter Defaults Property Page
The HPF Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter types.

The HPF parameter limits you can adjust are as below.

For 6 dB/oct filters, as well as Butterworth filters of all order, the cutoff frequency is the -3 dB frequency. For Linkwitz-Riley filters of all order, the cutoff frequency is the -6 dB frequency. For Bessel filters, the attenuation at the cutoff frequency varies with order.

The HPF Variable Q Parameter Defaults Property Page

The HPF Variable Q Parameter Defaults property page is shown below.

The HPF Variable Q Parameter Defaults Property Page
The HPF Variable Q Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

This Variable Q 12 dB/oct LPF filter type allows you to implement several HPF types as special cases. These are as follows.

When a Butterworth 12 dB/oct filter (Q = 0.707) is implemented with this filter type, its cutoff frequency is the -3 dB frequency. When a Linkwitz-Riley 12 dB/oct filter (Q = 0.5) is implemented, its cutoff frequency is the -6 dB frequency. For other values of Q, the attenuation at the cutoff frequency varies.

The LF Shelf Parameter Defaults Property Page

The LF Shelf Parameter Defaults property page is shown below.

The LF Shelf Parameter Defaults Property Page
The LF Shelf Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter types.

The parameter limits you can adjust are as below.

The LF Shelf Order 1 and LF Shelf Order 2 filters are for compatibility with the LS6 and LS12 filter types respectively of the Behringer DSP amps and DCX2496 processor. The LF corner frequency in Hz is best understood in the case where the boost in dB is very large. In such cases, the LF corner frequency is approximately the frequency for which the LF boost is 3 dB less than the maximum LF boost. This convention matches what Behringer uses in their DSP control software. See the Behringer filter compatibility table for more information about compatibility of MSO and Behringer filter types. An LF Shelf Order 2 filter is equivalent to an LF Shelf Order 2 Variable Q filter having a Q value of 1/sqrt(2) = 0.707.

Users of miniDSP hardware should use the LF shelf filters with "(Alt)" in their names instead. These filters use a "center frequency" convention that is more easily understood. See the documentation for the parameter defaults property pages for those filter types for more information about the meaning of the center frequency.

The LF Shelf (Alt) Parameter Defaults Property Page

The LF Shelf Parameter Defaults property page is shown below.

The LF Shelf Parameter Defaults Property Page
The LF Shelf Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter types.

The parameter limits you can adjust are as below.

The center frequency of the LF Shelf Order 1 (Alt) and LF Shelf Order 2 (Alt) filter types is defined as that frequency for which the boost (or cut) in dB is one-half the ultimate low-frequency boost (or cut) in dB. For instance, if the LF boost in dB were specified as 6 dB, that shelving filter will have a boost in dB that approaches 6 dB as the frequency approaches zero. If the center frequency were specified as 50 Hz, then that filter's boost value would be 3 dB at 50 Hz. An LF Shelf Order 2 (Alt) filter is equivalent to an LF Shelf Order 2 Variable Q (Alt) filter having a Q value of 1/sqrt(2) = 0.707. This gives a so-called "maximally flat" behavior.

The LF Shelf Variable Q Parameter Defaults Property Page

The LF Shelf Variable Q Parameter Defaults property page is shown below.

The LF Shelf Variable Q Parameter Defaults Property Page
The LF Shelf Variable Q Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

The LF corner frequency in Hz is best understood in the case where the boost in dB is very large. In such cases, the LF corner frequency is approximately the frequency for which the LF boost is 3 dB less than the maximum LF boost.

Usage of this filter type is not recommended, as equivalent behavior can be achieved using the LF Shelf Order 2 Variable Q (Alt) filter type described below. The LF shelving filters with an "(Alt)" designation use a center frequency conventions that's easier to understand than the corner frequency convention described above for this filter type.

The LF Shelf Variable Q (Alt) Parameter Defaults Property Page

The LF Shelf Variable Q (Alt) Parameter Defaults property page is shown below.

The LF Shelf Variable Q (Alt) Parameter Defaults Property Page
The LF Shelf Variable Q (Alt) Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

The center frequency of the LF Shelf Order 2 Variable Q (Alt) filter type is defined as that frequency for which the boost (or cut) in dB is one-half the ultimate low-frequency boost (or cut) in dB. For instance, if the LF boost in dB is specified as 6 dB, that shelving filter will have a boost in dB that approaches 6 dB as the frequency approaches zero. If the center frequency were specified as 50 Hz, then that filter's boost value would be 3 dB at 50 Hz.

This is the recommended LF shelving filter type to use in the MSO shared sub filter channel to achieve a target curve with a rising low-frequency response. See the target curve example for more information about this filter type and how to use it to generate and establish a target curve.

The LF Shelf Linkwitz Transform Parameter Defaults Property Page

The LF Shelf Linkwitz Transform Parameter Defaults property page is shown below.

The LF Shelf Linkwitz Transform Parameter Defaults Property Page
The LF Shelf Linkwitz Transform Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

The LF boost in dB of a Linkwitz Transform filter is equal to the boost you specify for this parameter, while the response approaches 0 dB (no boost or cut) at high frequencies.

The Linkwitz Transform filter is not usually used for subwoofer applications, except possibly by subwoofer vendors who use the advertised LF cutoff frequency of sealed subs for marketing purposes. It can extend the anechoic LF response of a sub by applying LF boost and setting Qp and Qz appropriately, using Thiele-Small theory. For most subwoofer applications, it's best to let the room modes boost the LF response below the anechoic cutoff frequency of the sealed sub (typically 40 Hz), then use PEQs to clean up any resulting in-room response irregularities. It is provided here for completeness.

The LF Shelf Linkwitz-Riley 4th-Order Parameter Defaults Property Page

The LF Shelf Linkwitz-Riley 4th-Order Parameter Defaults property page is shown below.

The LF Shelf Linkwitz-Riley 4th-Order Parameter Defaults Property Page
The LF Shelf Linkwitz-Riley 4th-Order Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

This is an experimental filter type created by the MSO author, meant only for main speakers, not subs. It is intended to be used in systems without a "classic" crossover. The complex summation of a fourth-order Linkwitz-Riley (LR4) LPF applied to the subs (with levels suitably set), and this filter applied to the main speakers results in the same all-pass response as that achieved using an LR4 LPF on the subs and an LR4 HPF on the main speakers. The difference is that using this filter on the main speakers instead of an LR4 HPF gives an overlap in the frequency range used by main speakers and subs, while avoiding the response hump that would otherwise occur without an attenuating LF shelf applied to the main speakers. The transition frequency of this filter must be the same as the -6 dB frequency of the LR4 LPF that's assumed to be applied to the subs.

This filter is only for experimental use by those who understand the theory upon which it is based.

The HF Shelf Parameter Defaults Property Page

The HF Shelf Parameter Defaults property page is shown below.

The HF Shelf Parameter Defaults Property Page
The HF Shelf Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter types.

The parameter limits you can adjust are as below.

The LF corner frequency in Hz can be thought of as the frequency at which the response begins to "bend upward" toward high frequencies if there is an HF boost, or "bend downward" toward high frequencies if there is an HF cut.

HF shelving filters have an LF gain that's fixed at 0 dB, while both boost and cut at high frequencies are possible. For Behringer compatibility, see the Behringer filter compatibility table. There you'll find that the HF corner frequency specified in the MSO filter reports must be used with Behringer devices. The LF corner frequency cannot be used directly with Behringer devices.

The HF shelving filters are intended to compensate for known inductance-related HF rolloff of subs, not rolloff introduced in measurements due to incorrect sub or AVR setup.

The HF Shelf Variable Q Parameter Defaults Property Page

The HF Shelf Variable Q Parameter Defaults property page is shown below.

The HF Shelf Variable Q Parameter Defaults Property Page
The HF Shelf Variable Q Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

The LF corner frequency in Hz can be thought of as the frequency at which the response begins to "bend upward" toward high frequencies if there is an HF boost, or "bend downward" toward high frequencies if there is an HF cut. HF shelving filters have an LF gain that's fixed at 0 dB, while both boost and cut at high frequencies are possible.

The HF shelving filters are intended to compensate for known inductance-related HF rolloff of subs, not rolloff introduced in measurements due to incorrect sub or AVR setup.

The HF Shelf Linkwitz Transform Parameter Defaults Property Page

The HF Shelf Linkwitz Transform Parameter Defaults property page is shown below.

The HF Shelf Linkwitz Transform Parameter Defaults Property Page
The HF Shelf Linkwitz Transform Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

The HF boost in dB of an HF Shelf Linkwitz Transform filter is equal to the boost you specify for this parameter, while the response approaches 0 dB (no boost or cut) at low frequencies. The LF corner frequency in Hz can be thought of as the frequency at which the response begins to "bend upward" toward high frequencies if there is an HF boost, or "bend downward" toward high frequencies if there is an HF cut.

The HF shelving filters are intended to compensate for known inductance-related HF rolloff of subs, not rolloff introduced in measurements due to incorrect sub or AVR setup.

The All-Pass Order 1 Parameter Defaults Property Page

The All-Pass Order 1 Parameter Defaults property page is shown below.

The All-Pass Order 1 Parameter Defaults Property Page
The All-Pass Order 1 Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

All-pass filters have a magnitude response that's flat at 0 dB over all frequencies, and a phase shift that varies with frequency. The phase shift of first-order all-pass filters is 0 degrees at high frequencies, and goes to +180 degrees at low frequencies. These filters have a single parameter, the center frequency. This frquency is sometimes called f90, as it is the frequency for which the phase shift from input to output is +90 degrees. The optimizer can vary this center frequency over the range you supply here for the minimum and maximum center frequancy values.

The All-Pass Order 2 Parameter Defaults Property Page

The All-Pass Order 2 Parameter Defaults property page is shown below.

The All-Pass Order 2 Parameter Defaults Property Page
The All-Pass Order 2 Parameter Defaults Property Page

This property page is used to establish parameter value limits for the following filter type.

The parameter limits you can adjust are as below.

All-pass filters have a magnitude response that's flat at 0 dB over all frequencies, and a phase shift that varies with frequency. The phase shift of second-order all-pass filters is 0 degrees at high frequencies, and goes to +360 degrees at low frequencies. Second-order all-pass filters have two parameters: the center frequency and Q. The center frquency is sometimes called f180, as it is the frequency for which the phase shift from input to output is +180 degrees. The optimizer can vary the center frequency and Q over the ranges you supply here for the minimum and maximum center frequancy and Q values.

The value of Q affects the flatness of the group delay. A Q value of 1/sqrt(3) = 0.577 gives a Bessel all-pass filter, which has a so-called "maximally flat group delay". Values of Q higher than this will yield an all-pass filter with a peak in its group delay before it drops toward zero at high frequencies, while Q values less than 1/sqrt(3) will give a group delay that gently sags toward zero at high frequencies.