Here's the graph with just the TEAC settings plus the old TDA1543 NOS:
There's that early roll off with the ASUS Essence One previously measured.
PCM 24/384 (more than DXD [352.8 kHz]!):This is a "pseudo-test" actually. The fact is that the E-MU 0404USB is incapable of digitizing at 384kHz so what I did was upsample the 24/192 test signal using SoX so see if running the TEAC at the higher sampling rate will cause a measurable loss in the analogue output dynamic range or worsen noise characteristics within the measurable capability of the E-MU.
Summary of PCM Results:
What I found surprising was the option to allow the digital filter to be turned "OFF"; I don't recall any reviewers spending much time on this (even the AudioStream review just glossed through this and didn't comment on the sound). This setting puts the DAC into a "NOS mode" where digital interpolation is suspended - this appears novel especially in a device with low-jitter asynchronous USB interface and a true 24-bit (err... ok, 32-bit as if that makes a difference) DAC... In general NOS DACs these days are still based on obsolete decades-old DAC chips like the Philips TDA154x (16-bit) or Analog Devices AD1865 (18-bit) which tend to perform poorly on measurements. Although personally I am not a big fan of the roll-off and aliasing distortion, some have commented on subjective improvement by taking out the digital oversampling filter, so I definitely consider it a positive that TEAC offers this option for anyone to try (in real time with instantaneous A-B'ing no less just by turning the knob)! I can certainly see this option useful to tone down some of the overly "bright" digititis-inducing recordings. Looking at my pop CD collection, an example where this was demonstrable was Jason Donovan's disco-inspired Too Many Broken Hearts from Ten Good Reasons (first pressing, 1989) where the OFF setting was more tolerable after 3 minutes :-). As a compromise, the SLOW filter may be reasonable.
As I mentioned at the beginning, PCM remains the cornerstone of digital audio. These TEAC UD-501 results suggest that nothing has been sacrificed in terms of performance in the PCM domain. Note that the ASUS Essence One is also based on the PCM1795 chip in dual-mono configuration but doesn't measure as well, highlighting the importance of the electronics around it like the analogue output stage, power supply and USB/coaxial/TosLink interface circuitry affecting the final output quality. One thing I wish the TEAC had from the ASUS is the beefier headphone amp though.
Bottom line: these results are consistent with the excellent subjective sound quality described in the previous UD-501 blog post. I would happily present some kind of award if it meant anything :-).