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Re: What's the problem with "brick wall" filtering?

Posted by Soundmind (A) on December 2, 2006 at 05:36:23

In Reply to: What's the problem with "brick wall" filtering? posted by Don T on December 2, 2006 at 05:00:47:

Analog filters can be designed and built to perform identically to digital filters. It can be more complicated though depending on the specifically desired characteristics of the filter. Analog filters can be arranged as successive sections. It is probably best to isolate one section from another with active devices to prevent interaction. The cascading of these sections can be used to arrive at the final result. But there are drawbacks to each method. Each analog stage will introduce some noise and distortion but if the number of stages are reasonably small, the net effect of this degradation will be inaudible. Also, tolerances of LCR need to be kept tight. Digital filters for audio OTOH rely on the linearity of A/D and D/A circuits to avoid distortion and offerings today are excellent. Because DSP based digital filters can be easily reprogrammed very precisely, a general purpose digital filter such as an equalizer is probably a better choice due to cost and flexibility but both types can give excellent results. Look at the 61 band digital equalizer in the Parts Express catalog. It is a fine performer and value.

For an "infinite slope" loudspeaker crossover network, active digital filtering is clearly the better choice over analog passive or active filtering. The reason is IMO that any mismatch between sections will result in an overall FR anomoly ranging from an unintended 3 db rise if they overlap to a notch which can only be described as a chasm if they underlap.

"In reality does redbook present filtering issues that can't or aren't practically overcome? Or is this brick wall filtering issue really a non-issue?"

IMO, today it is a non issue. Dissatisfaction with most well made RBCD recordings and equipment stems from other factors which include poor loudspeaker design to the lack of the editing methods used in the old days by recording engineers who had to adjust final mixdowns keeping the limitations of their analog formats, principally tape and and vinyl in mind. That's practically a lost art. If you want to test the RBCD system yourself, burn a CD from a vinyl and AB them. I think you'll find that even with your home consumer type audio equipment, the results are very close.

BTW, for those whose religion is dead set against "equalizers", in addition to the equalization inherent in EVERY stereo analog format from RIAA for LPs, NAB, for tape, Dolby A, B, and C for both, and 75 microsecond compensation for FM, realize that a crossover network is an equalizer because it is a filter network. These frequency selective circuits are all conceptiually the same. Only cds and other digital formats don't need to deliberatly use equalizer circuits in the audio passband.

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