Hi, Monty -- very nice explanation. However on the question of resampling not affecting quality, that cannot be quite true. Every time you apply a filter (digital or analogue) it spreads out transient features ever so slightly. Most obvious example is a wavelet, e.g. applying an FIR filter length N to a wavelet length M gives an output wavelet length N+M -- it spreads it out. Every single filter in the chain of processing is a compromise between making endless waves look perfect (long FIR) and not blurring transient features too much (short FIR). So if resampling involves a lowpass anti-aliasing filter, then it cannot be perfect. However in practical terms, we can hope it is "good enough" not to be noticeable by humans, which I guess is your point. (Although I've heard 'radio-tuning' noises when outputting a pure rising-frequency sine-wave through a resampling hardware output (e.g. 44.1 to 48kHz) so in some cases the compromises in the design ARE clearly noticeable.) BTW I am the author of the open-source filter design software Fiview. --Jim
Nothing involving a filter is ever perfect
Date: 2013-02-28 10:13 am (UTC)