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RE: Why not?

Posted by Jim Austin on November 2, 2016 at 11:05:07:
>>But many engineers have asked: "What if multiple ADCs were used to record a single track? And what about cascading DACs?" How can one possibly correct for all of that?<<

A reasonable question, to which I can only provide a schematic (not exact) answer. I suspect a schematic answer is the best you're going to get (not that mine is the best possible). The MQA folks refer to their work on such projects as "white-gloving," the meaning of which is, I think, obvious. Bob and I talked a lot about this, especially in the context of early digital recordings. He said they've been studying a large cache of albums--about 10,000 high-res and about 10,000+ at CD resolution. In this way, they've learned a lot about what typical albums look like from a time-smear perspective and what problems arise. (Bob didn't say, to me, that their algorithm uses "artificial intelligence," although he did use the phrase. He said--I didn't check the transcript, but this is the gist--that it was sort of like artificial intelligence.)

I suspect though that the correct answer is, you can't correct for all of that, but you can correct for some of it. Which is to say, you can create a version of the recording that sounds better, not perfect.

As for your proposed "demo" track: that certainly would be interesting. Way back in February, I requested (not sure who I was communicating with then--possibly Stuart) graphical evidence: Show me what a transient, in real music, looks like before and after. I don't remember what the response was, but I never got the plot. However, something very close to that was published on the Stereophile site in the Q&A with Bob Stuart; look at graphs 8-13. Those plots are made using a DAC emulator because there's a basic measurement problem: To get a real signal out, you'd need to use an ADC and then reverse its characteristics.

Anyway, maybe we'll see something like that someday, but satisfying the skepticism of a few audio writers probably is not at the top of their to-do list.

>>Now to your problem -- my past life installing networks would say: "Ok, that's a problem for you and we might have to reduce the bandwidth - for YOU." (Providing other solutions don't work.) But what about me and countless others who don't have the issue -- why do we want to use a lossy compression scheme when we really don't have to?<<

Ah, I see your point. You're worried about the fact that it's not lossless, strictly speaking. I think this is a reflection of a shift of emphasis from the technicalities of the format to what's actually happening in the music. To worry about a bit of loss in the compression algorithm is to assume that every bit is equally important. As noted in several MQA documents, above a certain frequency there's no real information anyway--no information related to the music. Compressing that in a lossy way doesn't do a lot of harm. (I recall shaking my head the first time I saw the phrase "partial zero-emission vehicle" on the side of a Subaru. Compression in MQA is kind of like that: Partly lossless, partly lossy.)

Anyway, you can't always get what you want. I'm going to not finish the Stones reference. That would be too cute.

jca