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Posted by Charles Hansen (M) on May 18, 2017 at 18:00:18

In Reply to: Thanks for clearing that up.... posted by AbeCollins on May 18, 2017 at 16:23:11:

Your DAC is indeed receiving a FLAC stream of 48/24. The problem is that not all of those bits are being played back as music without decoding. Even with full hardware decoding, a 192kHz file will be limited to a maximum resolution of 17.2 bits. This only makes sense, given that there is no such thing as a free lunch. How else could a losslessly-compressed file be further compressed? Something has to give, and with MQA it is a combination of lossy compression of the quad-rate data plus discarding the bottom bits in the baseband (single-rate) data.

MQA apparently asserts that the at least 6.8 (and possibly as much as 11.8) of the lower-order bits are inaudible. We have all heard that claim before, specifically when we were told that MP3 compression provided "CD quality". The maximum possible resolution MQA can achieve (decoded or not) is 17.2 bits. While this can result in excellent sound quality, it also result in a loss of resolution - both measurable and (to my ears, at least) audible.

Bit depths of 24 or greater are not necessarily required for delivery to the playback system. But they are absolutely required in the studio when post-processing (ie, mixing, EQ, reverb, and many other effects) to maintain 16-bit resolution of the final product. While it is true that 24 bits of real resolution *may* not be audible to a skilled listener, I would hesitate to state that as a fact until actually tested. As JA notes in his "Measurements" sections, many modern DACs are able to achieve 19 or even 20 bits of actual resolution. When he tested the Meridian Explorer2 he concluded "With 24-bit data, the noise floor drops by 16dB or so, suggesting resolution approaching 19 bits."

This near 19 bit resolution of the Meridian Explorer2 exceeds the resolution of MQA files. This was borne out in listening tests using the Explorer2 comparing both the original 96/24 of The Doors "Riders on the Storm" with the MQA version available on Tidal. From Wikipedia, "Jim Morrison recorded his main vocals and then whispered the lyrics over them to create the echo effect"(see link below). When listening to the full high-res file on a good system (or headphones), it is quite easy to hear the whispered overdub as a distinctly separate element in the mix. I cannot say the same for the MQA version. To my ears the "whisper overdub" was markedly more difficult to discern. Please try it for yourself and let me know what you think.

As always, my posts here are strictly my own opinions and not those of my employer, family, friends, neighbors, pets, or enemies.

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