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Something still seems wrong here

Posted by Charles Hansen on June 5, 2017 at 22:40:21:
>> you could choose your own filter: Fast, slow, MPh. These choices apply only when the MQA filter is disabled. So I checked. It's set to MPh. MQA filter is also MPh. I guess it's the same MPh, or very close. <<

I still don't fully understand what is happening here:

1) The Mytek Brooklyn uses the ESS ES9018K2M DAC chip. I am very familiar with it as it is the same model that was very first used in the Pono Player. It has a choice of three stock digital filters built into it, which correspond to the choices offered by the Brooklyn:

The top graph is the "Fast" filter, the middle graph is the "Minimum Phase" filter, and the bottom is the "Slow" filter. The ESS chip is somewhat unusual in that its internal filter is a concatenation of a 4x initial stage followed by a 2x stage for a total of 8x. (Virtually all other DAC chips use a concatenation of three 2x stages.) As you can see, the frequency response of the Minimum Phase is virtually identical to the Fast filter. Instead of having �10 cycles of both pre- and post-ringing, it has ~20 cycles of post-ringing only (there's no free lunch).

NB: You can estimate the number of taps in each stage by counting the number of "bumps" or "ripples" in the stop-band response. The "Slow" filter has about 15 taps and it appears that all calculations are done in one pass. The first (4x) stage of the Fast and Minimum Phase filters probably has almost 100 taps, while the second (2x) stage appears to have about 9 taps. This is a total of (say) 109 taps, whereas doing it in a single pass with the same frequency response of the first section would require 200 taps - which is why companies concatenate filters - it saves money. (These are just some of the "fingerprints" left behind by digital filters that give us clues into what is causing the spectra you have been posting.)

But the MQA filter looks nothing at all like any of the ones built into the ESS DAC chip. That filter's behavior is clearly seen in JA's review, linked earlier. Furthermore my understanding of the MQA digital filter is that it is implemented in an external DSP chip, typically an XMOS - which is what is found in the Mytek Brooklyn.

It still seems something is amiss. I am completely confused that (the other) JA was able to measure the response of the MQA filter, apparently without access to a special MQA test file that would activate the MQA filter. It also seems that somehow the MQA filter was active in the second spectrum you posted. Normally all CD recordings will yield a spectrum like the first one you posted, where the energy falls off a cliff right around 20kHz. If MQA were more forthcoming in the details of how their system worked, we wouldn't have to scratch our heads on this. If you have the time and interest, I would suggest a couple of further tests you could try:

1) Run the spectrum of the CD on the Brooklyn with the MQA both engaged and disengaged.

2) If you don't see a difference there, try comparing the CD spectrum from the Brooklyn with the spectrum obtained from a different D/A converter.

3) If you want to get really hard core, have (the other) JA send you a copy of the -4dBFS white noise file he uses to recreate the test Juergen Reich of MBL created. This allows one to examine the stop-band response of a digital filter, allowing you to remove the variable of the spectral content of the music on your CD.

As always, solely my personal opinions and not necessarily those of my employer or your employer.