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In Reply to: RE: How is Archimago's equipment not "up to the task"... posted by Jaundiced Ear on January 27, 2016 at 19:50:44
Abe has a valid point that Archimago's test equipment is not up to the task of measuring hi-res digital audio sources. However, Abe's point is irrelevant to this topic since Archimago is simply analyzing the files in software and not measuring anything.
I think his analysis is fine for what it is, but it doesn't really shed any light on the more controversial claims of MQA. Claims such as "MQA corrects for errors at the A/D and D/A stages" are unverifiable via any real world measurement system that I can think of. Which is quite convenient for Meridian and all the press that have joined the marketing effort, and guarantees that we'll be arguing about this in audio forums for some time.
Follow Ups:
How about the nulling in Audio DiffMaker to below -70dB? If the differences, if any, are so far down in the mix do we really need to worry about them? I'm just thinking back to the days when we only listened to LPs with phono cartridges with at best -30dB channel separation and -30dB was, at least to my ears, essentially no output at all. Certainly I enjoyed broad stereo images at the time!
JE
"A difference which makes no difference is no difference at all." - William James
I think you're looking at it the wrong way. In theory, MQA encoding should be transparent to the source at least to the 16-bit level, so you should not see -77 dB differences between the files.
What should we be seeing then?
JE
"A difference which makes no difference is no difference at all." - William James
Let me put it this way: What good is an encoding scheme intended for high-res audio if it's not even transparent to the 16-bit level?
As I understand MQA, perhaps incompletely or inaccurately, the corrections it applies are in the time domain, mainly as a result of apodizing filters in the a-d and the d-a, including those DACsin current pre-MQA Meridian players. These filter ringing issues are visually verifiable now. I have seen enough scope traces in reviews, etc. to understand the high frequency pre- and post-ringing that occur both in the recording itself from the a-d and in the DAC from the d-a. Those scope traces are abundant, as are those showing improvement as the result of apodizing d-a filters.
I believe it is possible for MQA processing of the recording to apodize and to clean up that ringing in the recording, provided the a-d filter characteristics are known. When played back on a non-MQA DAC, this can still provide an audible advantage, though the non-apodized d-a will introduce its own pre/post ringing. When played via an MQA DAC, apodizing also reduces pre/post-ringing from the d-a. Possibly, my understanding is oversimplified.
The point is, scope traces, which are measurements, ought to be able to show these improvements. I have not seen them yet for MQA. But, I believe we will someday. I also tend to believe, for now, in the potential audible advantages of the apodized filter approach.
The major problem to me is not the theory of MQA, though, like many, I do not claim to fully understand it yet. The problem is with the timing of public announcements, the limited amount of technical information they contain, wide availability of good comparative A-B listening auditions, etc. The roll out process seems to have jumped the gun as far as we consumers are concerned, with many negative opinions so far, based on too little actual evidence.
Perhaps Meridian were seeking only to offer enough to first be able to bring Tidal, etc. into the fold as major sources of MQA encoded material, apparently with some success. They wanted to do this first before making a major investment in mass producing chipsets and software for the mass market. That might be prudent from a business standpoint.
But, we consumers are left with only teasers, resulting in speculation, skepticism or downright antagonism to this new, but not yet fully understood, technology. What we have mainly are raves only by audio gurus, whose objectivity might be questionable. To many, that sounds like hype. But, even audio gurus are not always wrong.
Time will tell. My mind is still open.
The only way to remove ringing added by the anti-aliasing filter at the front end of the chain is to make the cutoff frequency of the reconstruction filter lower than the anti-aliasing filter.
Anyway, looking at the impulse response of a reconstruction filter is misleading because an impulse is an impossible signal. The digital signal being converted by the DAC is necessarily band limited prior to and during A/D so it can't be an impulse.
Note that if the signal contains no (or at least very little) spectral content at or above the cutoff frequency of a brick wall filter, the filter will not add ringing. That condition is nearly impossible to satisfy with 44.1 KHz sampling, but fairly easy to satisfy at 88.2 KHz and above.
So the issues with hard band limiting at 20 KHz don't apply to high sample rates. And since MQA is designed to be an efficient container for high sample rate recordings, I can't see the justification for introducing a FR roll-off equivalent to 10m of air in order to obtain a visually appealing impulse response. This would not be an improvement IMO.
I think MQA is trying to be too many things at once. I like the idea behind the packing method. But I'm not happy it's tangled up with a scheme to license Meridian tech at both ends of the chain, on a basis that is technically questionable, and backed by a marketing campaign that is confusing and in part misleading.
Maybe I'm being too skeptical, but I have a feeling that Meridian is being intentionally vague so they can't be pinned down.
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