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In Reply to: RE: But what about...? posted by Doug Schneider on May 24, 2017 at 04:02:48
>> But to make it to designers or people who know better then not be willing to show one bit of evidence to prove what you're saying -- even though it would be very easy to -- then that's another. If they did prove that, I'd be much happier. Till then... <<
It would seem that they are relying on listening tests to "prove what they're saying". The difficulty is it appears that none of these are true apples-to-apples comparisons. Specifically the MQA files are always played back through the MQA slow-rolloff minimum phase digital filter, while all other files are played through a different digital filter - almost always the stock one found in the DAC chip.
There are quite a few manufacturers who have taken the trouble to learn how to design and implement custom digital filters. The reason to spend the required time, resources, and increased parts cost is because those manufacturers believe they can build a better-sounding digital filter than the stock ones found in DAC chips.
The main conclusion one could reach of those that prefer the sound of MQA files would seem to be that MQA has created a digital filter that sounds better than the stock digital filters found in DAC chips. Which simply supports the notion that manufacturers that use custom digital filters also have the opportunity to create better sounding products.
I suppose that it would also be possible to implement a custom digital filter that sounds *worse* than found in a typical DAC chip. This would also imply that various custom digital filter implementations have varying degrees of sonic performance. Since the MQA digital filter is a custom (ie, not off-the-shelf) digital filter, it would be logical to conclude that some custom digital filters sound worse than MQA's solution and that some custom digital filters sound better than MQA's solution.
If one accepts this premise, then it becomes clear that it is possible (and possibly likely) that there are DACs that will play back true high-res files and sound better than MQA files, as the original high-res file will *always* contain more musical information (better source material) which is then fed through a superior-sounding custom digital filter. An obvious bonus of this scheme is that if one purchases a DAC with a superior-sounding custom digital filter that it will sound better with *all* digital files and sources, and not just the small number of titles that have been encoded in MQA (which activates the MQA custom digital filter).
As always, my postings here reflect only my opinion and not necessarily that of my employer or the currently hottest pop star.
I agree that the nonexistent apples-to-apples comparisons is a problem.
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.
*IF* that works, I think it would be quite easy to demonstrate if they really wanted to.
> > 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.
This comment from you is interesting: "My understanding is that the MQA encoding process "corrects" ('de-blurs') errors in the existing digital file created by an imperfect A/D converter."
As a so-called "end-to-end" process, my understanding that the "correction" wasn't done in the actual encoded file but, rather, at the end, in the DAC itself, along with adjusting for imperfections in the DAC.
With that in mind, if, in fact, they are correcting the original file and that MQA file has been modified for A/D imperfections then the the entire thing is even more lossy than I first thought. First off, as you mention, the lower bits are gone and some compression goes in to getting it all into the 24/48 constraint they are using. Then, if a process that corrects for timing of the A/D was applied, well, that plain and simply alters the original file. Just one of those MANY questions I had (and have).
Someone just brought a post to my attention (linked below). This is from Gordon Rankin, who designed the award-winning AudioQuest DragonFly series of USB DACs. The latest two models have been designed with MQA in mind and last week a firmware update was released that allows for some sort of MQA compatibility.
I must say that I don't yet understand this process. Remember that software decoding of the first "fold" was a surprise only announced when Tidal began streaming MQA in late January. This is the first I've heard of "custom filters for each song" and leaves me with more questions than answers:
1) If there is specific filtering done for each song, why not do it during the encode process?
2) The scheme is very reminiscent of similar schemes patented for the A/D process by Pacific Microsonics for HDCD and for the D/A process by Ed Meitner and assigned to Museatex for the BiDAT DAC. Both processes had two separate filters (anti-aliasing for the A/D side and reconstruction for the D/A side). The units would automatically switch coefficients depending on the signal level in the top octave. Is there more to this in MQA's implementation? How many sets of filter coefficients are available?
3) The DragonFly DACs will not normally decode signals higher than a 96kHz sample rate. My understanding is that the software decoding performed in the Tidal software only outputs a maximum sample rate of 96kHz. Does the DragonFly do anything more than fine-tune the filter coefficients?
It would seem that MQA is still under development. Interesting times. As always these posts are my opinions only and not necessarily those of my employer or previous employer.
> > if a process that corrects for timing of the A/D was applied, well, that plain and simply alters the original file < <
Yes, the original high-res file is altered in at least three ways:
1) The quad-rate audio data is compressed using lossy techniques.
2) The lowest 6 to 8 bits in all frequency bands are discarded to allow the dual- and quad-rate information to be "folded" underneath the audio data in the baseband. This is claimed to be "inaudible" as it is below the noise floor of the electronics. However it is well known that the ear/brain can distinguish correlated music 10dB or even 20dB below the noise floor of an LP, for example.
3) The so-called "blurring" in the original file is created by the digital anti-aliasing filter used in the A/D converter. This "ringing" is at a specific frequency - the corner frequency of the anti-aliasing filter - typically Fs/2. One concern about this filtering process is to ensure that new artifacts are not introduced.
In this sense MQA is like MP3 - both are lossy processes and the full original data can never be recovered.
All postings are strictly my own opinion and not necessarily those of my employer or my kids.
..and Doug, did you now that around the end of last year/beginning of this year, Meridian/MQA fired their US based PR firm? They now handle all inquiries direct. Why?,,, the audiophile press (you excluded!!!) has been their de facto PR service, at no cost.
> Doug, did you now that around the end of last year/beginning of this year,
> Meridian/MQA fired their US based PR firm?
Meridian's PR is indeed now handled from the UK. MQA's US PR is still
handled by Sue Toscano, who has been responsible for the account since
the start, first with Nicoll PR and now with her own company.
"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.
*IF* that works, I think it would be quite easy to demonstrate if they really wanted to."
They can't and won't. Because in a word, it is utter bullshit.
And if we stretch our imaginations to their absolute limit, and suppose they they have unlocked the secret to flawless digital encoding, why not design an ADC that fixes ALL issues, this supposed "smearing" at the start.
The answer is clear.
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