MRC01
Major Contributor
Agreed that is what would happen and the way most DACs actually work. My point is that from a theoretical perspective, regardless of how DACs actually work, the set of sampling points - the audio data - has an infinite number of different solutions, many of which don't even have the original passband frequencies that were encoded to create them. Bandwidth filtering is theoretically necessary in order to reconstruct the wave that was encoded, because there are an infinite number of entirely different waves that all pass though those exact same sampling points. Even if a real-world DAC would never actually construct any of those other waves, they are all valid solutions and it is only bandwidth filtering that narrows the set of possible solutions to just a single wave.OK, but to generate 32.1 kHz instead of 12 kHz, you'd need to either suppress (filter) the fundamental so only the image is present, or up sample using a scheme that also suppresses the fundamental. Both are do-able, using W-S or one of many other schemes, but AFAIK that is not what a conventional (delta-sigma or not) audio DAC would implement. ...
I think I'm lost, sorry... The theory is sound, but I do not see it happening in an audio DAC. That is, images will be present if not filtered, but the baseband signals will still be there.
You are not lost at all. My point has all along been from the perspective of theory.