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RE: There's no free lunch

Posted by Charles Hansen on May 22, 2017 at 19:25:07:
>> why don't you send your DACs to Meridian so they can take it apart and get the blueprint <<

The very first audio company to promote slow-rolloff "gentle" digital filters (to the best of my knowledge) was Wadia in the late 1980s. Wadia was formed by a group of digital engineers who left 3M to make their fortune in high-end audio. At that time there were only two companies in the world to have their own custom digital filters (made using DSP chips), Wadia and Theta. Everybody else used a digital filter chip designed by the semiconductor manufacturer, initially either Philips or Sony, later from Pacific Microsonics, later mostly from Burr-Brown or Analog Devices, and currently mostly from ESS, AKM, and Wolfson. There are now more than two companies with custom digital filters (some using DSP chips and others using FPGAs, but they still comprise the minority in this area (Ayre, dCS, Chord, PS Audio in their latest products designed by Ted Smith, Aesthetix, Schiit in their top model(s?), Auralic just recently announced at least one model, and a few more I'm sure I'm forgetting).

Slow-rolloff digital filters didn't hit the mainstream until Pioneer adopted them in the early '90s, calling this feature "LegatoLink". Pioneer's purchasing volume was large enough that Burr-Brown included a slow-rolloff option in their digital filters. Ayre was the first (to the best of my knowledge) to use this Burr-Brown digital filter in a high-end product, the D-1 DVD/CD player, released in the late '90s. The digital filter could be selected by the user via a toggle switch on the rear panel labeled "Listen/Measure". The slow-rolloff ("Listen") position yields superior performance in the time domain (less ringing - or as MQA calls it, "time blur"). This comes at a cost in the frequency domain as there is a -3dB rolloff from 15kHz to 20kHz. (This is all part of the "no free lunch" rule.) If one reads the reviews, the "Listen" position is almost universally favored. The slight rolloff in the very top half-octave is practically meaningless given the variations in frequency response due to loudspeakers, headphones, rooms, and individual hearing.

Three decades after Wadia, MQA seems to have discovered the benefits of using a slow-rolloff filter. At the 192kHz sampling rate, the MQA process has a -3dB point at around 33 kHz - roughly 1/3 of the 96kHz Nyquist frequency used by typical "brickwall" digital filters. I suspect this is the reason that some like the sound of MQA - the MQA-mandated slow-rolloff digital filter sounds "better" than the sharper digital filter found in most DACs.

But even this is up for debate. Take a look at JA's recent review of the Chord DAVE DAC, priced over $10,000. It has a brickwall filter with tens of thousands of taps, and the most pre- and post-ringing of any digital product JA has measured. Yet he found the sound of that unit to be excellent also. It would seem that there may be some other factors at play that are as yet unidentified.