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RE: Charles, Please tell me if this makes sense.

>> This is a 44.1/24 recording. The gap seems centered on the Nyquist frequency. <<

I'm sorry to say that I don't know if this makes sense or not. It seems many of us are looking for additional information regarding the entire MQA encode/decode process, and this could be a helpful clue. I'm assuming that the light green trace is the CD - so far, so good. Then if the magenta trace is the MQA version, questions start to arise. All of the examples published by MQA I've seen only seem to address files that are multiples of 48kHz. I am as yet unclear on is how MQA handles files recorded at multiples of 44.1kHz.

Andreas Koch of Playback Design says in an a YouTube interview that the MQA process sample-rate converts files recorded at multiples of 44.1kHz to multiples of 48kHz (scroll forward to 6:25):


This seems to be supported by the patent application that can be found on the Benchmark Audio website, which shows a 96kHz input signal being fed to a noise shaper that separates the signal multiple times, both into high- and low-frequencies and also into upper- (first 17 and later 13) and lower-bits (included are links to the original MQA patent applications):


The next point that is unclear about the graph you posted is if the MQA version is supposed to represent the original 44.1/24 file or a higher resolution 88.2/24 file. If the former, it raises several questions, such as "What is the signal above the Nyquist supposed to represent?" and "Why not just encode it directly to FLAC for universal compatibility and a smaller file size?" If the latter, then other questions arise such as, "Does the MQA FLAC wrapper play back at 44.1kHz or 48kHz?" (you should be able to tell by the display on your DAC) and "What happened to the audio signal in the notch?" (a non-MQA processed 88.2/24 file would have no such notch).

At this point it appears that there is a bug in the MQA "unfolding" process, which is surprising to me. One would think that they have had both the resources and the time to work all of the bugs out. Yet the evidence seems to indicate that working with files based on multiples of 44.1kHz are not processed correctly, either in the encoding ("folding") or decoding ("unfolding") side. If in fact the audio is sample-rate converted, that could explain some of the variable reactions to different MQA titles. As Andreas Koch points out, sample-rate conversion is a lossy process - all of the original data is discarded and replaced by interpolated replacements.

I personally have never heard a sample-rate conversion that was transparent. The first time I ran into this was listening to a music video DVD with the soundtrack recorded at 48kHz. I liked the music so much that I bought the CD, apparently made by sample-rate converting to 44.1kHz. The sound of the CD was distinctly worse than the DVD even when played on the identical system, exhibiting a coarse and unpleasant graininness. I've heard similar effects from outboard sample-rate conversion boxes when making non-integer rate conversions (eg, 44.1kHz to 96kHz instead of 88.2kHz). In my experience, the less one fiddles with the raw data, the better the final results.

As always these posts reflect only my opinions and not necessarily those of my employer or fellow inmates.

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