What actually is apodizing?

[Doobrey]

My Arcam SA20 with ESS9038 has many filter options and the default is set at apodizing linear phase, not knowing what this is I read up on it a little bit and found this

“Apodizing filters are generally used to correct/reduce errors in the source data, introduced by the ADC digital decimation filters, or at later stage conversion tools used to produce the final deliverables. Such errors can for example add artificial sheen on the highs, such as cymbals.”

So it’s a less steep linear phase something between sharp and slow to reduce the ringing?

I know there’s always been a debate about the audibility of ringing and from what I’ve read about that is with high quality records it’s inaudible but with poor mastering and compressed it is audible.

I mostly listen to modern “crappy” sounding music, what would be the correct filter to set and forget? Apodizing linear / fast linear / brick wall?

 

[DonH56]

An apodizing filter is a modified filter form often used in DSP systems (not just audio). Mathematically, it can look like a window function on an FFT. Practically speaking, it modifies the typical high-order "brick wall" anti-imaging output filter to reduce pre- and post-ringing. Better time response traded for somewhat slower roll-off. In photography, an example apodizing filter is a modified neutral-density filter that gets darker towards the edges, leaving the center clear, so it helps reduce glare and such while leaving the center clear. The audio version accomplishes the same idea on an impulse (which does not normally occur in music).

Whether the ringing is audible is a big subject for debate. The ringing itself is at very high frequency, but the envelope it creates depends upon the filter design and may be fairly long, thus lower in frequency.

Chances are you would be fine with any of them, but my suggestion is to pick a song you like and know very well, and try all three to see if you can tell them apart. If I was to just pick one blind, I'd choose the apodizing filter and call it a day.

FWIWFM - Don