That's exactly the non-intuitive---and frankly, amazing---part about noise shaping. If you measured the noise across the entire frequency range (0-45.2 MHz), you'll find precisely the amount of total noise power that you would expect to see from a 1-bit quantizer: a lot. But by controlling very precisely when the unit switches back and forth between the 0s and 1s, the effect is to shape the frequency response of that noise---so that most of it lies well above the audible range, and is easily filtered out.

Ah, now that's the bit I never knew (I designed one of these as a degree project -- it didn't get built 'cos it was too many gates for the FPGA, but it wouldn't have made a 44.1kHz DAC anyway as the chip was only clocked at a few MHz).

Good scheme this, post all sorts of nonsense on the BBS and have people who actually know about stuff point out the places where I don't. Cool!

So your 2048x oversampling DAC basically has a lookup table of 65536 2048-bit patterns, one for each possible PCM input, and just shifts out the right one at 90Mhz? And the cleverness is in designing the 2048-bit patterns?

Peter