The block diagram you linked to confirms exactly what I said (see Fig 7A). 17 bits come out of the LF/HF splitter. But only the 13 most significant bits are losslessly encoded as the 13 most significant bits in the output PCM. The next 3 bits are “lossy”.
Following that are 4+4=8 bits of encoded MQA data.
I’ll be generous and say that the effective “lossless” bit depth (before noise-shaping") is 16 bits. A critic would say “13 bits”.
Why are we leaving this one alone? The whole discussion in the other thread (from which our comments were yanked) was about 16/44.1 MQA on Tidal.
Sorry, but everyone (including Bob Stuart) agrees that the compression block in Fig. 7A is lossy. It is just not possible to fit losslessly-compressed 96kHz data into the 8 LSBs of a 48kHz file.
I heartily agree that the ultrasonic “content” here is
inaudible
mostly electronic noise
(Obviously, you understand that if there really were audio content out to 70-80 kHz, you’d need to sample at more than twice that frequency to capture it. 24/48 MQA is only supposed to unfold to 96kHz, which would (lossily!) capture audio signal out to 48 kHz.)
You don’t sacrifice noise.
By truncating to 16 or 13 bits, you raise the level of the quantization noise.
With 24/44.1 MQA, you lower the SNR from 24 to 16 bits (which, IMHO is perfectly fine).
With 16/44.1 MQA, you lower the SNR from 16 to 13 bits (which is not fine).
This is not about the SNR of the original recording. I suggest you Google “quantization noise”
Dithering helps (especially noise-shaping dither). Everyone mastering a 16/44.1 audio file applies noise-shaping dither. But applying dither to a 13-bit signal does not get you anywhere close to high fidelity.
Again, I am perfectly fine with the proposition that 24 bits are superfluous and (provided you dither the 16 most significant bits), you can use the 8 LSBs of a 24bit PCM file for steganography, with no audible loss of quality.