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RE: your assumption is erroneous: born out by experience

Apodizing filters belong in the recording process. They do not belong in the playback process. If they were used in the recording process then many of the high frequency problems with Redbook playback would not be present. The problem is that recordings made properly with apodizing filters sound dull when played back with another round of apodizing filters, whereas recordings made with brick wall filters can (usually) be improved by playing them back with apodizing filters. This situation exists only because of the incompetence of Sony and Philips in specifying the Red Book standard. As a result, for best CD playback listeners have to select between a set of filters on a per recording basis, a situation akin to the early days of LPs, pre RIAA. (A few years ago, I simply gave up on tweaking filters. I just accepted the fact that no 44/16 digital recording could ever be considered to be high end and as such can never be a suitable reference for evaluating a playback chain. With CDs, one must simply accept their limitations and enjoy the music or else move on to better formats if the artists are still alive and recording with better technology.)

All of this is easy to verify by starting with a high resolution digital recording and downsampling it to Redbook with various filters and then playing it back with various filters. It can also be measured on spectrum plots or seen in impulse response plots. I speak from a fair amount of personal experience on this matter, as well as a fair amount of theoretical understanding. I have spent many hours experimenting with apodizing (and other) digital filters, measuring their performance and listening to how these filters affect sound quality. In each case, I started with a reference of how the particular recording was supposed to sound and the specific degradation imposed by the limitations of the 44/16 format and the conversion processes used (which were state of the art).


From a marketing perspective, the situation is obscured because of the variety of recordings and the variety of playback systems. Some playback systems start out too bright and in this case an apodizing filter serves as an upper treble "tone control", and in some cases multiple apodizing filters provide much needed high frequency roll-off. This is a characteristic of poor system setup, and has nothing to do with the digital filtering. These set up problems can be identified using high resolution digital recordings and corrected by appropriate measures, typically involving speaker placement, cross-over adjustments or room treatments.


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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