One particularly interesting feature is the use of "minimum phase apodizing digital filter" which replaces unnatural pre-ringing of traditional linear phase filter with a more natural impulse response - which eliminates pre-ringing and aliasing distortion, as well as reduces post-ringing. This type of filter is based on Peter Craven's 2004 AES presentation and is currently used by a small group of digital audio manufacturers including Meridian, dCS and Ayre (see white paper for more details.) With the exception of Wolfson's WM874x chip family, apodizing filters are not standard in most of today's off-the-shelf DAC chips, so companies had to resort to customized DSP solution.
While it does not say how exactly Lindemann executed digital filtering in the USB-DAC, but quoting from its top of the line 825 CD player "...To maximize resolution, the digital signal is processed by a Blackfin DSP. The code used is a Lindemann proprietary further development of the well-known Anagram Sonic 2. In addition the original linear phase filter has been replaced with a much better sounding minimum phase filter with “apodizing behaviour”. This type of filter effectively suppresses time domain artefacts (including those present in the recording) by replacing the original impulse response with a new one with virtually no pre-ringing..."
The fully balanced, ultrafast output section with current feedback exhibits virtually perfect time domain behavior (But why no balance output?.) The output stage also features low negative feedback, the first-order analog filter and the lack of OpAmps.
