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RE: on another note Charles...

>> Will the ESS minimum phase slow filter on the Oppo 205 likely approximate what you have done with "MP"? <<

Good question, but hard to say with any certainty. The only real way to know is with listening tests, but there is enough information that we can say "probably not". Although both are described as "slow rolloff, minimum-phase digital filters", there are many differences we can see and likely more that we can't see. About the only visibility I have into the ESS filter comes from the datasheet, which is not publicly available. It shows graphs of both its frequency response and its impulse response. Based on that alone, there are significant differences between the filters. Ayre's single-rate slow rolloff MP filter has about 1-1/2 cycles of post-ringing, while the ESS has about 4-5 cycles of post-ringing.

We have a few data points to help us predict the audibility of this difference. Ayre DACs with a "Listen"/"Measure" filter selection allow the choice of two minimum-phase filters, one with about 20 cycles of post-ringing, the other with 1-1/2 and the difference is fairly easily noticed. In contrast when JA recently reviewed the Meridian Ultra DAC (link below), he found it virtually impossible to hear any differences between minimum-phase filters, the shortest with about 6-7 cycles of post-ringing and the longest with ~35 cycles of post-ringing. Based on these two sets of data points, I suspect that the filter length alone would create an audible difference between the filters. However I also suspect that the slow rolloff MP filter in the ESS DAC chip would be my preference of the 7 choices offered.

That is just the tip of the iceberg, however. While the digital filter is one part of the design that affects the sound, there are many other aspects to digital filter design not mentioned above, including the window shape, the dithering applied, the interpolation rate (ESS uses 8x, while Ayre uses 16x). Further there are many more factors that affect the sound of a D/A converter In my experience, digital filters are one of about a half-dozen major design aspects that will significantly affect the sound of a digital product. Also important are the analog circuitry, the power supplies, the clock implementation, the DAC chip itself, and the presence or absence of any DSP algorithms (such as Asynchronous Sample Rate Conversion - ASRC - and many others). I would be loathe to rank the importance of them, but would agree that the digital filter (or lack thereof, in the case of "non-oversampling") plays an important factor in the overall sound quality.

As always, strictly my own opinions and not necessarily those of my employer or trash collector.


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