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RE: But what about...?

Posted by Charles Hansen (M) on May 25, 2017 at 04:43:53

In Reply to: RE: But what about...? posted by Doug Schneider on May 24, 2017 at 18:17:15:

>> But this supposed "correction" they're talking about implies more than only the filter at the end. Supposedly, embedded with that MQA file, is information about the encoding A/D and that would then alter the behavior at the playback end to compensate for whatever errors were introduced at the start. <<

I don't think that MQA is claiming that the encoding process also sends information that alters the behavior of the D/A converter. My understanding is that the MQA encoding process "corrects" ("de-blurs") errors in the existing digital file created by an imperfect A/D converter. Then on top of that, when a D/A converter manufacturer applies for an MQA decoding license, MQA will analyze the digital filter already used and adjust the coefficients in the added MQA digital filter to "compensate" for the "imperfections" in that already present digital filter. This filter is already present because the vast majority of D/A converters are built with chips that incorporate the digital filter function and the DAC function itself into one chip (to reduce costs).

On the other hand there are a few D/A converter manufacturers who separate those two functions into two separate circuits because one can build a higher-performance digital filter than the cost-constrained designs that are built into DAC chips. The manufacturers that have taken this path have invested significant resources into developing what they feel is the highest possible performance, and may not be overly excited about the prospects of a third party modifying the digital filter they have developed. And conversely, manufacturers that lack the resources to design custom digital filters may be very excited for a third party to supply them with a digital filter that may out-perform those built into DAC chips.

Pacific Microsonics' HDCD process has many similarities to the overall scheme of MQA, as both claim to solve "problems" existing in (then) current digital technology, and both also sell (sold) digital filter chips (or algorithms) they claimed out-performed those commercially available. With HDCD, PM claimed their process increased the limited resolution of the 16-bit CD to 20 bits. A close examination reveals that there was actually only about a 1-bit increase in resolution due to their compansion (compression/expansion) process. The other 3 bits of claimed resolution improvement were actually achieved via dither - something that is not patented nor proprietary and hardly exclusive to HDCD. The slight increase in resolution became moot when *true* high-resolution formats were developed, including both DVD-Audio and SACD.

If MQA claims to improve existing digital files by "de-blurring" (removing time-smear introduced by the digital anti-aliasing filters in the A/D converters used to create the recordings), there is nothing to stop others from also developing digital filters that accomplish the same goal. In fact many already have. Furthermore it is also possible to develop A/D converters that have no "blurring" that adds artifacts to the original analog signal, and hence would derive no benefit from "de-blurring". And in fact many already have.

The other benefit of MQA is that it reduces file size through a combination of lossy compression and discarding the lower bits in the original high-res file. The resulting loss of resolution is claimed to be inaudible, just as was the case with MP3. In both cases the falling cost of digital storage and the rising speeds of network connections has largely negated the need for such compromises.

>> *IF* that works, I think it would be quite easy to demonstrate if they really wanted to. <<

It would seem there are many ways MQA could easily dispel the confusion and controversy surrounding the process. Many (besides yourself) wonder why they have not.

As always, these posts are my personal opinions and not necessarily those of my employer or my golf caddy.

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