Bit Depth Increase With Upsampling


I was refreshing my memory about dithering a while ago and it reminded me every doubling of rate by up-sampling increases bit depth by 1/2 bit (ie 3db) - with more sophisticated noise shaped dithering its a full bit per doubling. Since most CD’s use dithering this would mean say 16x oversampling is an effective increase from 16 bits dithered to 20 bits. But the DS goes much further than that - its 10xDSD ie 640 times and would be at least an extra 8 bits ie equivalent to 24 bits. Is this true? If so one could imagine reducing say 705k to 12 bits and get effective 20bits. If so you could probably have better impulse resolution at lower rates than MQA. I have always suspected MQA can be done in better ways. Oh to see why as you double the sampling rate total noise is the same by now its over twice the frequency range so in the audible band is halved.