How can DSP/amplifier manufacturers enhance the integration of their DSPs with FIRmaker?

AFMG SDK for DSP Communication Service

In order to facilitate the transfer of FIR filters to third party DSP software, AFMG provides manufacturers with an SDK for our DSP Communication Service. With this software development kit, the DSP manufacturer is able to develop its own server module that automates the communication with EASE Focus 3. This functionality significantly speeds up the work of sound system designers and consultants.

How many FIR taps does FIRmaker need? What is the latency of FIRmaker processing?

Various simulations and experiments have been carried out by AFMG. So far results indicate that a minimum of 250 taps at 48 kHz is required in order to achieve good performance for the majority of use cases. A number of 500 to 1000 taps are recommended for complicated setups.

Processing of 250 FIR coefficients at 48 kHz corresponds to 5 ms of latency.

Does FIRmaker optimization with only one FIR channel per cabinet work in practice?

It certainly does! — Field tests (some of which have already been published by AFMG) indicate that substantial performance improvements can already be achieved when using only one FIR channel per cabinet. The explanation is simply that the sound waves in the mid-frequency range have wave lengths of the order of the cabinet spacing in typical line arrays. It is not necessary to have a much higher resolution than that.

How many FIR channels make sense for my system?

FIRmaker can work on any level: FIR processing can be applied to individual transducers in a cabinet, to groups of transducers, to entire cabinets or to groups of cabinets (e.g. pairs).

For many practical applications one FIR-channel per cabinet seems to provide a good compromise between improved sound quality and required processing power. In principle, the optimized performance of the line array is determined by the spatial resolution of the sound sources to which FIR processing is applied.

What kind of FIR filters are needed?

FIRmaker FIR filters are non-symmetrical, complex-valued transfer functions. Despite their excellent performance they have a compact time behavior and a very smooth frequency response in both magnitude and phase. This, in turn, allows for implementation with a comparably low FIR tap count and low latency.

Currently, nearly every available DSP is capable of implementing the filters generated by FIRmaker.

How bad is the “pre-ringing” of the FIR filters? Won’t this make the loudspeaker system sound bad?

FIRmaker does not generate linear phase filters. As such, the filters are not symmetrical in time about the peak of the filter’s impulse response. There is no requirement for the filters generated by FIRmaker to have pre-ringing. The transient behavior of the system will not be influenced.

Does FIRmaker only work with external DSP controllers or amplifiers?

No, FIRmaker can also be used in loudspeakers equipped with on-board DSP. This applies for example to more sophisticated powered line arrays as well as to digitally steerable column loudspeakers.

In general, any possible combination of DSP / amplifyers / transducers within single or multiple cabinets or in a unified housing is possible as long as the hardware and DSP software allows storing of separate FIR filters into every DSP block.

Ahnert Feistel Media Group

Located in Berlin, Germany, AFMG® Technologies GmbH has created the industry standards EASE and EASERA software for acoustic simulation and measurement as well as their related products EASE Focus, AFMG SysTune, EASE Address and EASE SpeakerLab.

In cooperation with our partner company SDA Software Design Ahnert GmbH we develop and distribute software for:

Electro-acoustic and
room-acoustic modeling
Electronic and acoustic
measurements
Applications in
engineering and physics
RF and infrared
simulation

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