Multi-Sub Optimizer Reference (page 8)

Filter Compatibility With Available Hardware

MSO supports many filter types, and not all of them are compatible with all available hardware. Before adding filters, you should check the information below to make sure the filters you choose are compatible with your hardware.

Differences in the Definition of Parametric EQ "Q" Parameter for Different Hardware

The most important filter building block in MSO is the parametric EQ filter, or PEQ. This type of filter has a parameter called Q, which determines its bandwidth. Unfortunately, there is no single agreed-upon industry standard for how Q is defined mathematically for a PEQ filter. However, two commonly used conventions have emerged. One convention is the so-called "classic Q" definition used by MSO standard PEQ filters, some Hypex DSP amps and the Behringer DCX2496 electronic crossover among others. It is what's displayed in the MSO Properties window for a standard MSO PEQ filter. For this filter type, it is listed as "Q", without any additional notation in the MSO filter report.

Another convention was originated by Robert Bristow-Johnson, or "RBJ" for short. The Behringer iNuke DSP amplifiers use the RBJ convention for Q. To find out the "RBJ Q" for a conventional MSO PEQ filter, it's necessary to get this information from the MSO filter report. It is listed there as "Q (RBJ)". If you use a conventional MSO PEQ filter and constrain the "classic Q" to a maximum of 10 (which is the highest the iNuke supports), the Q(RBJ) will always be less than 10 as well. This is true because Q(RBJ) is always less then the "classic Q" for a given PEQ filter (see equation 10 on this page).

Unfortunately, this limits the maximum Q for the iNuke to something somewhat less than what it supports, which is not generous to begin with. For instance, if a standard MSO PEQ filter has a center frequency attenuation of 6 dB and a "classic Q" of 10, the Q(RBJ) would be 10 / sqrt(2) = 7.07 (that's A0 = 0.5 in the above mentioned equation). Beginning in version 1.23 of MSO, you can specify "Parametric EQ (RBJ)" filters, which use the Q(RBJ) directly in their internal implementation. If you constrain the Q of these filters to a maximum of 10 (the maximum for the iNuke), that will be equivalent to a maximum Q(RBJ) of 10 as well, thus allowing the full range of Q supported in the iNuke to be used.

Therefore, if your hardware uses the Q(RBJ) convention as the iNuke does, it's strongly recommended that you use the new "Parametric EQ (RBJ)" filters rather than the standard PEQ filters to allow you to make use of the full range of Q values supported by your hardware.

miniDSP Compatibility

If you use the biquad coefficient export feature of MSO and import the coefficient file into your miniDSP device, you needn't worry about Q at all.. To do this, enable biquad support using MSO's Tools, Application Options, Hardware dialog. Specify the number of available biquads and the sample rate in this dialog. After completing the MSO optimization, use MSO's Save Biquad Text for This Channel menu item in each filter channel of the Config View. Then, for each channel, import the resulting text file into the miniDSP as an REW file. See the miniDSP documentation on advanced biquad programming for details.

When manually entering PEQ parameters into a miniDSP device, you must use the RBJ Q. If you use this manual data entry approach though, you'll lose support for some of the more unusual filter types supported by MSO. The miniDSP hardware is compatible with all the filter types offered by MSO, but in order to get this full compatibility, you must use the biquad file technique for exporting from MSO and importing into the miniDSP device.

Behringer iNuke DSP Amplifier and DCX2496 Electronic Crossover Compatibility

The tables below show which MSO filter types are compatible with the Behringer iNuke DSP amplifiers and DCX2496 electronic crossover.

Behringer iNuke DSP Compatibility

MSO Filter Compatible Notes
Gain Block Yes -
Delay Block Yes -
Polarity Inversion Yes -
Parametric EQ See note Use "Parametric EQ (RBJ)" filters
LPF Butterworth 12 dB/oct Yes -
HPF Butterworth 12 dB/oct Yes -
LPF Bessel 12 dB/oct Yes -
HPF Bessel 12 dB/oct Yes -
LPF Linkwitz-Riley 12 dB/oct Yes -
HPF Linkwitz-Riley 12 dB/oct Yes -
LPF Variable Q 12 dB/oct No -
HPF Variable Q 12 dB/oct No -
LPF Butterworth 18 dB/oct Yes -
HPF Butterworth 18 dB/oct Yes -
LPF Butterworth 24 dB/oct Yes -
HPF Butterworth 24 dB/oct Yes -
LPF Bessel 24 dB/oct Yes -
HPF Bessel 24 dB/oct Yes -
LPF Linkwitz-Riley 24 dB/oct Yes -
HPF Linkwitz-Riley 24 dB/oct Yes -
LPF Butterworth 48 dB/oct Yes -
HPF Butterworth 48 dB/oct Yes -
LPF Linkwitz-Riley 48 dB/oct Yes -
HPF Linkwitz-Riley 48 dB/oct Yes -
LF Shelf Order 1 See note Use LS6
LF Shelf Order 1 (Alt) See note Use LS6 with LF corner from MSO filter report
HF Shelf Order 1 See note Use HS6 with HF corner from MSO filter report
LF Shelf Order 2 See note Use LS12
LF Shelf Order 2 (Alt) See note Use LS12 with LF corner from MSO filter report
HF Shelf Order 2 See note Use HS12 with HF corner from MSO filter report
LF Shelf Order 2 Variable Q No -
LF Shelf Order 2 Variable Q (Alt) No -
HF Shelf Order 2 Variable Q No -
LF Shelf Linkwitz Transform No -
HF Shelf Linkwitz Transform No -
LF Shelf Linkwitz-Riley Fourth-Order No -
All-Pass First-Order No -
All-Pass Second-Order No -

Behringer iNuke DSP filter compatibility table

Behringer DCX2496 Compatibility

MSO Filter Compatible Notes
Gain Block Yes -
Delay Block Yes -
Polarity Inversion Yes -
Parametric EQ Yes Use conventional Parametric EQ filters
LPF Butterworth 12 dB/oct Yes -
HPF Butterworth 12 dB/oct Yes -
LPF Bessel 12 dB/oct Yes -
HPF Bessel 12 dB/oct Yes -
LPF Linkwitz-Riley 12 dB/oct Yes -
HPF Linkwitz-Riley 12 dB/oct Yes -
LPF Variable Q 12 dB/oct No -
HPF Variable Q 12 dB/oct No -
LPF Butterworth 18 dB/oct Yes -
HPF Butterworth 18 dB/oct Yes -
LPF Butterworth 24 dB/oct Yes -
HPF Butterworth 24 dB/oct Yes -
LPF Bessel 24 dB/oct Yes -
HPF Bessel 24 dB/oct Yes -
LPF Linkwitz-Riley 24 dB/oct Yes -
HPF Linkwitz-Riley 24 dB/oct Yes -
LPF Butterworth 48 dB/oct Yes -
HPF Butterworth 48 dB/oct Yes -
LPF Linkwitz-Riley 48 dB/oct Yes -
HPF Linkwitz-Riley 48 dB/oct Yes -
LF Shelf Order 1 See note Use LS6
LF Shelf Order 1 (Alt) See note Use LS6 with LF corner from MSO filter report
HF Shelf Order 1 See note Use HS6 with HF corner from MSO filter report
LF Shelf Order 2 See note Use LS12
LF Shelf Order 2 (Alt) See note Use LS12 with LF corner from MSO filter report
HF Shelf Order 2 See note Use HS12 with HF corner from MSO filter report
LF Shelf Order 2 Variable Q No -
LF Shelf Order 2 Variable Q (Alt) No -
HF Shelf Order 2 Variable Q No -
LF Shelf Linkwitz Transform No -
HF Shelf Linkwitz Transform No -
LF Shelf Linkwitz-Riley Fourth-Order No -
All-Pass First-Order No -
All-Pass Second-Order No -

Behringer DCX2496 filter compatibility table