Working with IIR Filters in FIR Designer

The IIR tab & Branded Modes | Reference Editor & IIR Conversion | Auto IIRs

The IIR features & functionality built into FIR Designer (& FIR Designer M) are invaluable when equalising individual loudspeakers or entire systems, creating combination IIR+FIR loudspeaker presets &/or working with different audio processor brands.

IIR tab screenshot with branded modes
The IIR tab in FIR Designer with the IIR filter mode menu open

The ‘IIR Filters’ tab & Branded Filter Modes

The ‘IIR Filters’ tab is a key part of the DSP design workflow in ALL our filter tools, enabling the selection & emulation of any IIR based filtering that will be used in the processor.

Available built-in filter types include parametric, low and high shelf, notch, band-pass, all-pass, and low-pass & high-pass Bessel, Butterworth, 2nd order variable Q, Chebyshev I & II, Elliptic, Linkwitz/Riley & Neville Thiele notched crossovers.

Since common parameters in many standard IIR filters produce different results on various amplifier/processor brands, a ‘Filter mode’ option on the IIR tab allows a specific branded mode to be used so that the IIR filter behaviour matches the chosen processor.

Brands with their own IIR filter mode include Biamp Tesira, Blaze Audio, BSS, Lake, Linea Research, Marani, Pascal Audio, Powersoft, QSC Q-SYS, RAM Audio, RMS Acoustics and Symetrix. (A full-featured ‘Generic’ mode is also provided which can be used as a starting point with brands without their own mode.)

(Branded filter modes are available in FIR Creator EX, FIR Designer & FIR Designer M.)

The Reference Editor & IIR Conversion

Accessed directly from the ‘IIR Filters’ tab, the IIR Reference Editor facilitates the swift creation of presets or tunings with identical IIR performance across different brands.

Set any brand as the ‘Reference’ then – in a single click – convert IIR filter settings to another brand, with an exact match.

(Where two products don’t have equivalent filter types, additional filters can be added & adjustments performed manually to ensure an exact match.)

Additionally, a measurement (in a supported file format) of an IIR response from a processor can be loaded into the ‘Target’ tab, and filters in the ‘IIR Filters’ tab can be set to match the target; using any of the branded IIR filter modes.

(The Reference Editor & brand conversion is available in FIR Designer & FIR Designer M only)

Auto IIR

Dramatically speed up the EQ process by automatically selecting & setting parametric filters to match a response to a target response.

The ‘Auto IIR’ function is accessed from the ‘IIR Filters’ tab & works with the non-branded ‘Generic’ mode and any of the branded IIR filter modes.

Key parameters to set for auto IIR generation include desired input smoothing, frequency range & the number of filters (to match the available number on your processor). Automatically generated IIRs can be added to the IIR tab with a single click, where they can be turned on/off and adjusted just like any other IIR filter.

All IIR filters (whether manually or automatically created) can be exported directly from the ‘IIR Filters’ tab, or as part of a combined FIR+IIR preset from the ‘Export’ tab.

(AutoIIR is available in FIR Designer & FIR Designer M only)

No IIR Mode for the Brand You Need?

When working with processors without a branded IIR mode, the ‘Generic’ mode is the best place to start. It includes parametric, bandpass, notch, low and high shelf, low-pass and high-pass Bessel, Butterworth, Chebyshev I & II, Elliptic, Linkwitz/Riley filters, as well as Neville Thiele notched crossovers. (The ‘Generic’ mode uses the Robert Bristow-Johnson Q & BW definitions for many filters.)

We recommend trying all available modes within the FIR Designer IIR tab, and comparing the plots displayed with the IIR plots generated by your own control software to determine which mode produces the closest match. (You may find one of the other branded modes provides a closer match than the Generic mode.)

Manually adjust the filters in the IIR tab until the response mimics your desired response. Then you can optionally set it as the ‘Reference’, so its filter set can be converted to other brands with the IIR Reference Editor.

Audio Providers of DSP-enabled audio devices (e.g. processors, amps, & related control software) are invited to provide Eclipse Audio with the necessary information for inclusion of a branded IIR mode in our software tools.
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Providers of DSP-enabled audio devices (e.g. processors, amps, & related control software) are invited to provide Eclipse Audio with the necessary information for inclusion of a branded IIR mode in our software tools.

IIR Export

IIR filter parameters and raw coefficients, created within the ‘IIR Filters’ tab, ‘IIR Reference Editor’ and the ‘Auto IIR’ window, can be exported to text files and the parameters copied to the desired control software. (Some specific IIR filter export formats are also available, such as CSV or QSC Q-SYS and WAY EQ for Ram Audio & RMS Acoustics.)

The export process is automated (via Direct-To-Processor functionality) for Powersoft, Marani, Lab Gruppen & Lake Processing. (Note: the Lake FIR 3-way & XP modules and the Lab Gruppen IPX series amplifiers, can accept raw IIR filter coefficients generated by any of the branded IIR modes.)

The ‘IIR Filters’ tab is part of the workflow for all our DSP design tools. The ‘IIR Reference Editor’ and ‘Auto IIR’ features are available in FIR Designer M & FIR Designer, and accessible only with software licensees. (They are not available in free demo versions of the software.)