44.1 vs 88.2 ABX report at AES Reply #50 – 2010-07-20 13:13:35 Quote from: Cavaille on 2010-07-20 08:40:03Arnie, you suggested to improve this test by upsampling the downsampled material to the samplerate the original had. I very much see the logic in your suggestion. However, may it be that brick wall filtering could introduce audible obstacles into the signal that are unwanted?I think that the audibility of brick wall filtering in the downsampling is the actual object of the test.QuoteI´m referring to the thread "Audibility of 20kHz brick wall filtering". So far (only three people have participated, including me) it seems that brick wall filtering may be audible. Further tests by several people are required however.If I understand that test properly, it has a serious limitation - the program material being used is implulses, not real world music. Even impulsive sounds in music far fall short of the extreme spectral content of a steady stream of impulses. Listening to impulses is about as much fun as listening to white noise.QuoteAnd it is my impression that both downsampling & upsampling use brick wall filtering to avoid aliasing artifacts for downsampling and imaging products for upsampling. Is that assumption correct?It is my understanding that downsampling uses brick wall filtering, but that upsampling either uses no brick wall filtering at all, or uses brick wall filtering at the nyquist frequency of the higher sample rate. It is very hard to avoid brick wall filtering in digital, so that's rarely the goal. As I understand it, the major goal of higher sample rates is raising the frequency of any brick wall filters.QuoteSo, if I´m using brick wall filtering two times, wouldn´t that be even more audible? Or am I getting this wrong?I think that the frequency of the corner frequency of the brick walls is highly significant. I don't think that anybody disagrees with the idea that in general, the higher the better. The only questions I'm aware of are how high, and what phase response is required for sonic transparency.