@jrp ahh good spot thanks - i did the synthesised one this morning on the other computer and forgot it's at a different sr. if you zoom in on the perfect one which is measurably & audibly free of artifacts you still see a picture like your screenshot - as i understood it: the post-filter in a dac (and the bandwidth of the rest of the chain after that) cuts off everything over nyquist so by the time you hit the speakers it does look like it should? - if you imagine what that waveform in your screenshot would sound like played slowly, it has _a lot_ of loud harmonics way higher up to make those steep edged verticals happen. none of those make it out of the dac's circuits. so the rectangles are a picture of the sample but not of the sound. zen.