Some IIR filters may produce different results when used in various amplifier/processor brands. Common causes are differences in the way each brand’s software interprets some filter parameters, like Q and bandwidth (BW), and in the conversion between Q & BW. The differences typically appear in parametric (peaking) filters and shelf filters.

The plots below show various implementations of a 10 kHz 10 dB parametric filter. The upper row is for a sampling rate of 48 kHz and the lower for 96 kHz. There is no simple translation between the BW and Q in each implementation, so to help with the comparison, all have been manually & approximately matched by adjusting the BW or Q to give ~ +5dB at 5 kHz. Looking at the both the magnitude and phase, it’s clear that the implementations are different, particularly near the Nyquist frequency of 24kHz for the 48 kHz sampling rate. The 96 kHz implementations are more similar because Nyquist has been pushed out to 48 kHz. However even when overlaid there are subtle differences.

In the plots, the implementations in the right two columns (labelled Linea Research & Powersoft) each have unique equations to create 2nd order analog filters, which are then mapped to 2nd order digital designs using the Bilinear Transform with frequency warping. The plot on the left uses a method proposed by Sophocles Orfanidis which attempts to keep the digital filter shape close to the analog design near the Nyquist frequency. (This method is very similar to the implementation used by Lake Processing). For more details see the 1996 AES Paper “Digital Parametric Equalizer Design with Prescribed Nyquist-Frequency Gain.”

FIR Designer (& FIR Designer M) can be used to emulate IIR filters as part of a complete loudspeaker preset. Recent updates added three ‘IIR Filter Mode’ options (General, Linea Research & Powersoft) that address these alternative IIR implementations. The Linea Research & Powersoft modes accurately emulate IIR filters for these brands (for loading into System Engineer, and Armonia, respectively). The General mode is the default option and offers IIR filters common to all three modes as well as Chebyshev & Elliptic high-pass and low-pass filters and Neville Thiele notched crossovers.

When using FIR Designer to emulate IIR filters for other brands, we recommend trying all three modes within the FIR Designer IIR tab, & comparing the plots displayed with the IIR plots generated by your own control software to determine which mode produces the closest match. Note: the Lake FIR 3-way module can accept raw IIR filter coefficients generated by any of the three modes.

For all three modes, IIR filter parameters and raw coefficients can be exported to text files, & the parameters copied to the desired control software. This process is automated (via Direct-To-Processor functionality) for Powersoft & Lake Processing (and we’re hoping to have other brands implemented in the future).

Useful links

• Orfanidis DSP text book
• Audio EQ Cookbook – Formulae and Equations
• Robert Bristow-Johnson The Equivalent of Various Methods of Computing Biquad Coefficients for Audio Parametric Equalizers

Now available in FIR Designer 2.9 & FIR Designer M 1.1: Eclipse Audio has recently collaborated with Linea Research to offer a “Linea Research” IIR filter mode which provides accurate emulation of Linear Research filters, including the unique Hardman crossovers filters, when creating mixed IIR+FIR loudspeaker presets. FIR filters can be exported as SFI files and loaded into System Engineer, for use in Linear Research processors and amplifiers. https://www.linea-research.co.uk/

Also available is a “Powersoft” IIR filter mode whose Q parameter (for all-pass and peaking filters) now exactly matches Powersoft Armonia. Using the Powersoft Direct-To-Processor functionality, mixed IIR+FIR processing chains can be exported to XML and loaded into Armonia for use in Powersoft amplifiers. https://www.powersoft-audio.com/en/

Both the Linea Research and Powersoft IIR filter modes enforce parameter limits – gain, frequency, bandwidth & Q – specific to each brand.

In FIR Designer and FIR Designer M, all IIR filters from previous versions are grouped under a “General” IIR filter mode and include bandpass, low and high shelf, low-pass and high-pass Bessel, Butterworth, Chebyshev I & II, Elliptic, Linkwitz/Riley & Neville Thiele notched crossovers.

For all filter modes, IIR filter parameters and raw coefficients can be exported to text files.

When switching between IIR filter modes, FIR Designer and FIR Designer M make a best-effort automatic conversion of all filters, although some manual adjustment of bandwidth or Q may be necessary. Where filter types are unavailable, a similar filter type is chosen.

FIR Designer & FIR Designer M can export FIR filters in a variety of formats for loading into most FIR-capable products, including Lab Gruppen (LAKE), QSC, MiniDSP, Electro-Voice, Symetrix, Dynacord, BSS, DFM, Biamp & Apex.

Download a free demo (Windows or Mac) of either FIR Designer or FIR Designer M.

Please note, the FIR Designer 2.9 feature updates apply to all existing subscription licenses and any new perpetual licenses purchased. Existing perpetual license-holders – 2.8 and below – will receive a bug-fix update only. For more details see the FIR Designer Release Notes.

FIR Designer Release Notes    FIR Designer M Release notes

Build a complete loudspeaker preset for multiple channels simultaneously with FIR Designer M. It utilizes the same easy-to-follow workflow of FIR Designer but provides up to 6-way, simultaneous multi-channel filter design. Create finite impulse response (FIR) filters and complete mixed FIR + IIR filter loudspeaker presets for single and multi-way loudspeakers, using multi-way loudspeaker driver measurements. Simulate the combined multi-way frequency response and time/frequency (wavelet) behaviour.

FIR Designer M also includes a new integrated Help menu to further enhance the software’s usability.

Learn more about FIR Designer M or download a free demo (Windows or Mac).

Existing FIR Designer 1 license-holders are eligible for a USD $100 coupon towards the first-year purchase of FIR Designer M. Existing FIR Designer 2 license-holders are eligible to convert their license to a FIRd M license at no additional cost (just contact us to set it up).

Pre-existing FIR filters – from sources other than FIR Designer/Creator – can be loaded (with or without resampling) in FIR Designer & FIR Creator EX. The filters can then be pushed – in combination with FIR Designer’s IIRs, gain, delay and polarity settings – to select Lab.gruppen Lake Processing & Powersoft amplifiers via Direct-To-Processor (DTP) functionality.

This video shows how to side load audio FIR Filters into FIR Designer when pushing a DSP preset to the LAKE 3-way module.

Learn more about FIR Designer or download a free demo (Windows or Mac).

Existing FIR Designer 1 license-holders are eligible for a USD $100 coupon towards the first-year purchase of FIR Designer 2.2; just contact us.

A new, standalone version of FIR Creator is now available: FIR Creator EX offers the same advanced export options found in FIR Designer, including the brand-new Direct-To-Processor functionality for integration with Lake & Powersoft amplifiers. It will be priced at a one-off cost of USD$299+tax (vs. FIR Creator @USD$249+tax). Unlike the mostly static feature set of FIR Creator, FIR Creator EX will be updated as necessary to incorporate any new DTP integrations developed between FIR Designer & other brands (ie. in addition to Lake & Powersoft). However, beyond updating DTP functionality, FIR Creator EX won’t receive updates (apart from essential bug fixes), as our development efforts continue to be focused on the subscription-based FIR Designer.

See the Product Comparison Table to compare features of FIR Creator, FIR Creator EX & FIR Designer

The specific additions to FIR Creator EX (vs. FIR Creator) are as follows:

• Two additional FIR Filter sample rates: 12 and 24 kHz (FIR Creator has 44.1, 48 & 96 kHz)
• Three additional Export formats: Powersoft, Linea Research & EV/Dynacord (FIR Creator has text [inc. CSV], Binary & WAV) 
• Processor gain, polarity & delay settings (not available in FIR Creator)
• Generate complete loudspeaker presets via the processor channel summary setting export option (not available in FIR Creator)
• Direct-to-processor functionality (not available in FIR Creator):
  • To LAKE PLM, PLM+ & D series amplifiers. Requires the FIR Designer LAKE plugin and the LAKE FIR 3-way module, & works over a (fixed or wifi) network.
  • To Powersoft X, Ottocanali, Quattrocanali and DueCanali series amplifiers. Works via an XML file which can be loaded into the amplifier’s “Speaker EQ” or “Output EQ”.
  • Can optionally side-load pre-existing FIR filters (with sample-rate-conversion, if necessary) from other programs for transfer to LAKE &/or Powersoft (subject to their FIR tap limits).

Learn more about FIR Creator / FIR Creator EX or download a free demo (Windows or Mac).

Tell us which amplifier brands you’d most like to see facilitating direct-to-processor FIR Filters/DSP Presets from Eclipse Audio’s FIR tools

FIR Designer 2.4 now integrates with Powersoft amplifiers. Transfer a DSP signal chain directly from FIR Designer to Armonía for use in Powersoft amplifiers via our new DTP (Direct-To-Processor) functionality. Pre-existing FIR filters (from sources other than FIR Designer) can also be loaded – with or without resampling – and transferred in combination with FIR Designer’s IIRs, gain, delay and polarity settings.

DTP for Powersoft works via an XML file which can be loaded into the “Speaker EQ” or “Output EQ” on X, Ottocanali, Quattrocanali and DueCanali series amplifiers.

Powersoft is the second brand to offer close integration with FIR Designer (LabGruppen LAKE PLM, PLM+ & D series amplifier integration was released in FIRd v2.3). We’re hoping to provide direct integration with other amp/processor brands in the near future. In the meantime, FIR Designer can export data in a variety of formats for subsequent upload into most FIR-capable productsWe’d love your feedback: Which amplifier brands would you most like to see facilitating direct-to-processor FIR Filters/DSP chains from FIR Designer? Tell us here.

For more details on v2.4, see the Release Notes.

Learn more about FIR Designer or download a free demo (Windows or Mac).

Existing FIR Designer 1 license-holders are eligible for a USD $100 coupon towards the first-year purchase of FIR Designer 2.4; just contact us.