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RE: Thanks...

Posted by Charles Hansen (M) on May 23, 2017 at 16:28:12

In Reply to: Thanks... posted by Jim Austin on May 23, 2017 at 01:12:52:

>> Others have claimed to hear "artifacts" in MQA; I'm thinking of recording engineer Brian Lucey--but he's not specific. What else do you hear, other than the loss of resolution? Anything good? <<

The only fair way to do a true apples-to-apples comparison test is with a unit that performs MQA decoding. Then one can send it either MQA-processed files for decoding or the straight hi-res files from which the MQA files were derived. That way there are only two variables in the experiment - the first is the digital filter used during the MQA encoding and the second is the digital reconstruction filter used in the DAC. I have performed such listening tests with both a Meridian Explorer2 and a Mytek Brooklyn.

It is essentially impossible to know what the sonic impact of the digital filter used while encoding MQA. However it is much easier to understand the sonic impact of the digital filter used in the playback DAC. When playing an MQA file we know from the MQA patent that the digital filter is a very gentle affair with a very slow rolloff. A 192kHz file is down -3dB at ~38kHz and -10dB at ~50kHz (roughly an octave below the Nyquist frequency limit of 96kHz). When playing non-MQA files in those two DACs the digital filter built into the DAC chips are used. The Mytek Brooklyn uses the exact same ESS DAC chip as both the Pono Player and the Ayre Codex. While both of those devices bypass the internal digital filter and instead use a custom digital filter developed by Ayre, I am also familiar with the sound of the stock digital filter in that chip. This allows me to get at least a rough idea of the differences produced by the playback digital filter.

In addition to the noticeable loss of audible resolution in specific instances (presumably because MQA reduces the bit depth from 24 to a maximum of 17.2), in my experience I could generally hear other differences that were neither "good" nor "bad". Many tracks seemed to have a bass emphasis that was not present in the original high-res file. Whether that is good or bad is a matter of opinion, but it was definitely a (noticeable) change from the original file. I have no definitive understanding of why this would be so, as MQA claims that no EQ is performed and I have no reason to doubt them.

The bottom line is that the digital reconstruction filter used in a DAC will impact the sonic performance of that unit (along with many scores of other variables). It does not surprise me that many listeners prefer the sound of MQA's slow-rolloff digital filter over the digital filter built into the DAC chip of those units. Many other manufacturers have arrived at the same conclusion, starting with Wadia Digital in the late 1980s and following through with Pioneer's "Legato Link" from the early '90s, Ayre beginning with their first digital product, the D-1 DVD/CD player introduced in 1998, and now many other manufacturers (most often using slow-rolloff options available in DAC chips from ESS, Burr-Brown, AKM, and Wolfson).

The improved sound quality of Ayre's custom digital filter is available with any source. *Every* slow-rolloff filter will provide some degree of "de-blurring" (to use MQA's terminology) as the amplitude of the "ringing" introduced by the A/D converter's anti-aliasing filter is reduced. If the slow rolloff is combined with the so-called "apodizing" technique (whereby the ringing introduced by the anti-aliasing filter in the A/D converter is removed by using a lower cutoff frequency in the DAC's reconstruction filter), this so-called "de-blurring" can be taken to any level desired.

Whether it is worth purchasing new hardware to decode a proprietary format that currently is essentially only available from one source is a question that only the purchaser can answer.

As always, this post represents solely my own opinion, and not necessarily that of my employer or my bartender.

This post is made possible by the generous support of people like you and our sponsors:

Analog Engineering Associates

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