There is no best filter, there are tradeoffs to be done, but as Matthias Carstens described in the manual, p. 83, the new SD LD filter of the AK4493 (found in the new models ADI-2 DAC FS and ADI-2 Pro FS R BE, model comparison here: https://forum.rme-audio.de/viewtopic.ph … 6#p165706) seems to be very well done, more than simply a compromise.
SD LD (Short Delay Low Dispersion):
In theory, a filter should have as little phase deviation as possible over the frequency range, have as short a settling time as possible, an acceptable decay time, and provide the maximum possible frequency range without deviation. The stopband attenuation should be high to prevent aliasing. A latency as low as possible would extend the application possibilities to more than just listening to music.
The filter with the bulky name Short Delay Low Dispersion approaches this ideal quite well. It does not have the early treble
attenuation of the slow filters (see chapter 34.14), has a shorter settling time than Slow, an average decay time like Sharp, a phase maximum of only 9° at late 18 kHz (basically phase-linear in the audible range), and a latency of only 10 samples, so that it is also well suited for professional real-time monitoring. This makes it much more than just a successful compromise.
See manual chapter 34.10 - 34.14
https://www.rme-audio.de/download/adi2profsr_d.pdf
https://www.rme-audio.de/download/adi2profsr_e.pdf
and this summary:
http://nihtila.com/2019/10/18/dac-digit … 3-filters/
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13