A Simple Exercise in “ Practitioner Level ” FIR Filters
by Robert Bernecker
Inspired and informed by Pat Brown’s recent blog posts about FIR filters, I recently pushed forward into experimenting with what I have called “practitioner level” FIR filter implementation. It seems that the tools for which we have been wishing and asking all these years are finally be coming available. As an initial step into the world of FIR filters for technicians in the field, I set out to determine if it would be possible for practitioners in 2014 to “roll their own” FIR filters for basic functions like crossover phase correction.
Although long chains of multiple all-pass filters have long provided a means to achieve so-called “flat phase tuning,” such tuning is tedious and tends to be inexact. Also, many DSP units with a preset architecture do not provide enough filter slots to make such tuning practical. Alternatively, the Lake processor (now by Lab.gruppen) has for years offered the ability to implement flat-phase crossovers with steep slopes, but while the sonic benefits are widely accepted and praised, the cost alone keeps this processing from being a viable option for many smaller projects; furthermore, unlike an open architecture DSP with network I/O (as was used for this experiment), the input and output counts are more limited on the Lake processors. In this sense, it is conceivable a single DSP (Symetrix in this case) with Dante I/O could replace multiple Lake processors.
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