for a CD). This is down only 20 dB, which is 10 times the value of the 40 dB in the fast mode. (Remember, decibels are in logs; hence a doubling in decibels is a 10x increase.) Maybe a teenage kid can hear it. The slow mode will make the ringing of the filter to an impulse look better in the time domain but at the cost of a potential audible effect, at least for teens. In addition I note that no scientific study has shown the ear is not sensitive to group-delay flatness.

In the 96-kHz mode, the rolloff moves from 42 kHz to 28 kHz. The -3db point is constant at 48.9 kHz. In the 96-kHz mode the first fold tone for 20 kHz is 78 kHz and this is well rejected with both fast and slow filters (and your ears). In the 96-kHz mode, group delay flatness is 14 times better than CD with the filter in the same mode. As was the case for CD, the slow mode makes things three times better. However, now we are starting with very small variations in group- delay flatness as a result of the reduced requirements on the filter to have an extremely steep transition band when the signal is sampled at 96 kHz.

The effect of the shape of the impulse response of the filter in the time domain that results from moving from 44 kHz to 96 kHz sampling is easier is to appreciate directly in comparison to looking at group delay curves vs. frequency. Some people I know who are experts in sampled data systems (but not in audio) say the reduction in the ringing before and after the impulse might have some effect on the reconstruction of signal in the time domain. Audio Engineering Society conference papers have been presented giving more details on this, but I have not seen them make it to the society’s Journal, which critiques the materials in greater detail prior to acceptance.

The fast and slow filter responses will change the

shape of the impulse. I have no recommendations on which shape would be preferable. 96-kHz sampling is such overkill that small details of filter rolloff become inconsequential. From an engineering point of view, that is a good thing. The difference between reconstructing a signal at 96 kHz and reconstructing it at 44 kHz is clear for all to see on a scope. Whether the difference can be heard is still an open question, but given a choice I will go for the thing that measures well, if it does not cost me any more. In the case of the hardware, the cost impact is small. Software costs are still a major issue.

The bottom line with this DAC is that you lose only a bit in comparison to the best. However, you have at least an extra bit over the lower-cost universal DVD players as well as the AV receivers I am currently testing. The players I am currently testing are, under worst case specs, just 16-bit engines. However, that is all you need for CD playback, and that type of performance in mid-line products would have been impossible a few years ago.

Conclusion: at $450 this unit is a good deal without question, assuming the analog stage is not messed up.

-DAR

T$S

Excerpted with permission from The Sensible Sound, Issue 104, July/Aug. ‘05. Subscriptions to TSS can be purchased by calling 1-800-695-8439 or writing to: 403 Dar- win Drive, Snyder NY 14226.