Originally Posted by scottb
BTW, you must upsample to do apodising, or any digital anti-aliasing filtering, because the filter knee is so close to the Nyquist frequency. Whether you speak of the filtering being applied after upsampling, or as part of the upsampling process, is really a matter of semantics. From the perspective of upsampling the original digital signal, you must upsample in order to filter, and you must filter if you upsample.

Actually that's not the case. One of the things that we evaluated in our listening tests was a filterless ("non-oversampling") DAC. It was interesting but also had some problems. So we tried adding a notch filter at 22.05 kHz to remove any "ringing" that was present from upstream in the record/playback chain. This can easily be done without oversampling.

To our ears it made virtually no change to the sound whatsoever. But that is another story altogether...

Charles Hansen
Ayre Acoustics, Inc.