John_Atkinson

Note that in my article, I used, not a single sample at 0dBFS to test A/D converters, but a PCM test signal sampled at 384kHz with a white spectrum and a 60kHz bandwidth -see figs.4 and 5 at https://www.stereophile.com/content/zen-art-ad-conversion - that I converted to analog. I do use a single sample at 0dBFS for my tests of D/A processors, as this maps the reconstruction filter's coefficients. John Atkinson Technical Editor, Stereophile

Not on the magazine's website, no. But it was covered in the print magazine. John Atkinson Technical Editor, Stereophile

I was responding to the incorrect assertions made on this forum that I wrote that MQA was "lossless." I didn't and wouldn't. John Atkinson Technical Editor, Stereophile

Incorrect. My 2018 article on A/D conversion - https://www.stereophile.com/content/zen-art-ad-conversion - gave an example of how this was achieved using an A/D converter with a slow-rolloff antialiasing filter (a dCS 904's F4 filter) and a D/A converter with a slow-rolloff reconstruction filter (an Ayre QB9's Listen filter). John Atkinson Technical Editor, Stereophile

I am beginning to think that some people lack comprehension skills. I did not say MQA is "not lossy." What I wrote was that "While it is true that the bits in an MQA-encoded file are not the same as those in the original hi-rez file, this does not necessarily mean that the format is 'lossy' in the manner that MP3, AAC, etc are lossy." You omitted the final 9 words in that sentence, thus misrepresenting my statement. If you look at the measurements I have performed on lossy codecs like MP3 and AAC - see https://www.stereophile.com/features/308mp3cd/index.html - and APT-X and A2DP - see https://www.stereophile.com/content/chord-chordette-gem-da-processor-measurements - you can see that these codecs discard real music information and compromise the analog noisefloor in order to reduce the bitrate. MQA behaves differently from those codecs, and while the unfolded/upsampled bits are not identical to those in the original hi-rez PCM file, in theory no music information is lost and the analog noisefloor is that of the original recording. All I am saying that MQA is different in principle to codecs like MP3 etc. You are welcome, of course, to regard it as "lossy" John Atkinson Technical Editor, Stereophile

And as I wrote, regardless of your statements I didn't say MQA was lossless. John Atkinson Technical Editor, Stereophile

I didn't say "lossless." With all due respect, I think you didn't comprehend what I wrote: "While it is true that the bits in an MQA-encoded file are not the same as those in the original hi-rez file, this does not necessarily mean that the format is 'lossy' in the manner that MP3, AAC, etc are lossy." John Atkinson Technical Editor, Stereophile

It is definitely posted this morning. John Atkinson Technical Editor, Stereophile

With respect, you're missing the point. Jim trapped ChatGPT into a tautological loop: "MQA technology uses a technique called 'time-smearing' to compensate for the effects of time-smearing. ... time smearing compensates for time smearing ...time smearing compensates for time smearing ..." This has nothing to do with MQA per se. See the full essay at https://www.stereophile.com/content/chatbots-take-hi-fi-issues John Atkinson Technical Editor, Stereophile

I still think how MQA works is indeed elegant. It recognizes that with real-world music, the spectral energy falls off with increasing frequency and that the recording's analog noisefloor is higher than the 24-bit floor. (With my choral recordings, which have very low acoustic and electronic noise - see attached room tone spectrum - the noisefloor can be accurately encoded with an 18-bit word length.) The former means that the energy above 1Fs can be quantized with a small number of bits and the latter means that those ultrasonic data can be encrypted to resemble pseudo-random noise and buried in a hidden data channel in bits 19-24 beneath the analog noisefloor. There is a slight noise penalty but it is a fraction of a dB. And as noise is noise, you can't detect the buried data channel by ear. This buried data technique is called steganography and is widely used in telecommunications and video technology - however, because the bottom bits now contain information, the data's entropy is higher and FLAC can't compress an MQA-encoded file as much as it can a straight 24-bit audio file. As Jon Iverson wrote in the article I referred to in my earlier posting, MQA offers benefits to both the record industry and the consumer. The former is no longer allowing free access to its unencrypted masters; the latter gets an improvement in sound quality. (The saving in bandwidth is no longer relevant, except for people who don't have unlimited data plans and want to stream hi-rez audio to their phones.) The benefit to the consumer is the "deblurring" that I discussed in a 2018 article: www.stereophile.com/content/zen-art-ad-conversion. The post-Shannon sampling - see https://ieeexplore.ieee.org/document/843002 - allows the ADC/DAC chain to be optimized to preserve transient information. Again, this is not new; Post-Shannon sampling is used in video when you don't want image edges to be burred, as in cartoons and anime. The price to be paid for the deblurring is the introduction of a small amount of aliased image energy. When you consider the spectral distribution of real-word music, this aliased energy will lie below the recording's original noisefloor and is therefore inconsequential. Unlike Apple/Dolby Atmos, MQA has not done a good job of selling the benefit to the consumer, which is why everyone complains about losing open access. (Audio has been the only medium where there haven't been proprietary closed formats - no-one complains about Dolby Digital, DTS, Dolby Atmos, DVD, Blu-ray etc, etc, where there are large license fees involved for manufacturers wanting to offer those formats.) John Atkinson Technical Editor, Stereophile

Not shy. Everything I have had to say on MQA since 2014 is available on Stereophile's website, at www.stereophile.com/category/mqa . I also examined the band-splitting and buried data channel aspects of MQA in a series of posts on Audio Science Review earlier this year. See, for example, https://www.audio “science” review/forum/index.php?threads/mqa-deep-dive-i-published-music-on-tidal-to-test-mqa.22549/page-72#post-760938 https://www.audio “science” review/forum/index.php?threads/mqa-deep-dive-i-published-music-on-tidal-to-test-mqa.22549/page-72#post-760969 and https://www.audio “science” review/forum/index.php?threads/mqa-deep-dive-i-published-music-on-tidal-to-test-mqa.22549/page-79#post-762223 Other than the reduced need to keep streamed file sizes small, I haven't seen or read anything on this site or others that leads me to change my mind about the format's technical elegance. On the commercial aspects of MQA, which are monopolistic, I commissioned and published an article on this in early 2018: https://www.stereophile.com/content/mqa-benefits-and-costs To quote from that article: "Once securely in place in the industry, MQA would be very difficult to dislodge, and its very dominance would deter the development of newer, possibly better formats—or even discourage the retaining of such current alternatives as WAV, FLAC, etc., as viable choices in the marketplace." John Atkinson Technical Editor, Stereophile

Did MQA achieve this, or are they lying? No one is a better position to tell us than you. Why won't you tell us? I wanted to borrow an A/D converter fitted with the MQA encoder in order to examine its behavior in the time domain, as I had done for Charley Hansen's transient-perfect antialiasing filter. However, in order to be able to do so I would have been required to sign an NDA, which would have defeated the purpose. John Atkinson Technical Editor, Stereophile

I know you are "cracking wise" but dCS has always offered a very short antialiaslng fliter on its A/D converters to reduce the otherwise inevitable sinc-function ringing on transients. And the late Charley Hansen of Ayre was also concerned about optimizing time-domain behavior. He used a "moving averages" filter for the Ayre QA-9 A/D converter that I found produced a perfect impulse response, at the expense of allowing some low-level aliasing energy. At a sample rate of 192kHz this was inconsequential. Before Charley passed he sent me an experimental complementary reconstruction filter for the Ayre D/A converters. This allowed perfect time-domain behavior throughout the recording-reproduction chain, just as is claimed for MQA. That was ironic indeed, given Charley's hatred of MQA. For reasons unknown Ayre never released this reconstruction filter. John Atkinson Technical Editor, Stereophile

In that case, doesn't that mean that all sighted listening is "squat." And I wrote earlier in this thread that I organized a blind test of MQA that gave the opposite result, only to have other posters on this forum say that a single test doesn't mean anything. I assume they will point that out to you also. John Atkinson Technical Editor, Stereophile

With respect, you are disregarding all the other listening tests and comparisons in which I have taken part. Yes, those were almost all sighted - you can find them all on the Stereophile website. However, given that Audiophile Style, like Stereophile, publishes reviews based on sighted listening, are you really saying that sighted listening doesn't produce reliable results? John Atkinson Technical Editor, Stereophile